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  • 1993  (2,728)
  • 1
    Electronic Resource
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993), S. 75-76 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 2
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 3
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993), S. 243-253 
    ISSN: 0886-9383
    Keywords: Orthogonal expansion ; Mapping ; Modelling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we discuss the orthogonal expansion of data matrices and its application to mapping and modelling. Two new methods, modified optimal discriminant plane (MODP) for mapping and order Gram-Schmidt orthogonalization (OGSO) for modelling, are proposed and examples are given.
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  • 4
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 5
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    Journal of Chemometrics 7 (1993), S. 381-392 
    ISSN: 0886-9383
    Keywords: Factor analysis ; Kolmogorov-Smirnov test ; Non-parametric tests in factor analysis ; Non-parametric test for principal components ; Principal component analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Each eigenvector of the dispersion matrix [X]T [X] was shown to be a partial predictor of the original data matrix [X], the sum of the predictions from the individual principal components being equal to the expectance of [X]. By comparing the distributions of the members of two neighbouring predicted matrices, [X̃]1…i and [X̃]1…i+1 (i.e. the sums of the first i and i + 1 individual predictions respectively), it was shown that they should be indistinguishable provided that i is equal to or greater than the effective rank of [X], and significantly different otherwise. This was confirmed by analysing the visible absorption spectra of methyl orange and methyl red solutions as well as the Raman spectra of Na2SO4 and MgSO4 solutions. On the grounds of these findings, a non-parametric goodness-of-fit test for assessing the effective rank of [X] was proposed which proved to be comparatively conservative and more robust than most currently used tests.
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  • 6
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    Journal of Chemometrics 7 (1993), S. 369-379 
    ISSN: 0886-9383
    Keywords: Simulated annealing ; Constrained background bilinearization ; Calibration ; Two-way bilinear data ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Generalized simulated annealing (GSA) is an optimization technique for locating the global optimum. In this paper GSA was used as the optimization procedure in the constrained background bilinearization (CBBL) of two-way bilinear data in order to reduce the possibility of sinking into local optima. The behaviour of the algorithm and its comparison with the modified Powell algorithm were studied by simulations and real fluorescence excitation-emission data for organic dye mixtures.
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  • 7
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 7 (1993), S. 439-445 
    ISSN: 0886-9383
    Keywords: Calibration ; Rank annihilation ; Residual bilinearization ; Three-way ; Trilinear ; Net analyte rank ; Second-order ; Generalized rank annihilation method (GRAM) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Through theoretical analysis and computer simulation, this short communication comments on the residual bilinearization (RBL) method and compares it with non-bilinear rank annihilation (NBRA) for the treatment of second-order calibration with non-bilinear data. It is found that these two methods are mathematically equivalent but have different noise propagation properties. The second-order advantage, namely quantitation in the presence of unknown interferences, can be carried over to non-bilinear data only if there exists a net analyte rank (NAR) for the analyte of interest.
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  • 8
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    Journal of Chemometrics 7 (1993), S. 495-526 
    ISSN: 0886-9383
    Keywords: Standard errors ; Eigenvalues ; PCA ; MLR ; GRAM ; Rank estimation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New expressions are derived for the standard errors in the eigenvalues of a cross-product matrix by the method of error propagation. Cross-product matrices frequently arise in multivariate data analysis, especially in principal component analysis (PCA). The derived standard errors account for the variability in the data as a result of measurement noise and are therefore essentially different from the standard errors developed in multivariate statistics. Those standard errors were derived in order to account for the finite number of observations on a fixed number of variables, the so-called sampling error. They can be used for making inferences about the population eigenvalues. Making inferences about the population eigenvalues is often not the purposes of PCA in physical sciences. This is particularly true if the measurements are performed on an analytical instrument that produces two-dimensional arrays for one chemical sample: the rows and columns of such a data matrix cannot be identified with observations on variables at all. However, PCA can still be used as a general data reduction technique, but now the effect of measurement noise on the standard errors in the eigenvalues has to be considered. The consequences for significance testing of the eigenvalues as well as the usefulness for error estimates for scores and loadings of PCA, multiple linear regression (MLR) and the generalized rank annihilation method (GRAM) are discussed. The adequacy of the derived expressions is tested by Monte Carlo simulations.
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  • 9
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    Journal of Chemometrics 7 (1993), S. 559-566 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 10
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    Journal of Chemometrics 7 (1993) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 11
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    Journal of Chemometrics 7 (1993), S. 61-73 
    ISSN: 0886-9383
    Keywords: Compression ; Multivariate analysis ; B-splines ; Maximum entropy ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For efficient handling of very large data arrays, pretreatment by compression is mandatory. In the present paper B-spline methods are described as good candidates for such data array compression. The mathematical relation between the maximum entropy method for compression of data tables and the B-spline of zeroth degree is described together with the generalization of B-spline compression to nth-order data array tables in matrix and tensor algebra.
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  • 12
    ISSN: 0886-9383
    Keywords: Factor analysis ; Window factor analysis ; Multicomponent analysis ; Ultraviolet spectroscopy ; Cu(II) complexes ; Ethylenediaminetetraacetic acid ; EDTA ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Window factor analysis (WFA) is a self-modeling chemometric technique for obtaining the concentration profiles of components from evolutionary processes such as chromotography, titration and reaction kinetics. By specifying the ‘window’, i.e. the region along the evolutionary axis indigenous to a component, the concentration profile of the component can be obtained without recourse to any information concerning the other components. Mathematical expressions required to perform such computations are derived. The method is applied to the investigation of copper(II) complexation with ethylenediaminetetraacetate (EDTA) by recording and factor analyzing the ultraviolet spectra of aqueous solutions containing a fixed amount of the disodium salt of EDTA and varying amounts of CuCl2. Evidence for four different species of EDTA is obtained. Clues concerning the stoichiometry of the species are garnered from the concentration profiles.
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  • 13
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    Journal of Chemometrics 7 (1993), S. 131-142 
    ISSN: 0886-9383
    Keywords: Classification ; Discriminant analysis ; Class modeling ; Specification limits ; Cross-validation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: There are many chemical products where product conformity is decided upon by qualitative human judgements of overall product quality. Nowadays, quantitative instrumentally determined quality parameters become available which are intended to replace such qualitative judgements by means of automatic decision rules using multivariate specification limits. Six classification methods to derive such limits are compared in terms of their power to predict corresponding human judgemets on overall color conformity of 17 dyestuffs based on historical quality data. Standard statistical classification methods turned out to be unacceptable for the routine generation of decision rules because of the frequent distinct suboptimality of their predictive power. Instead, a simple non-statistical classification method utilizing a priori knowledge about the underlying data structure yielded uniformly satisfactory decision rules.
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  • 14
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    Journal of Chemometrics 7 (1993), S. 153-163 
    ISSN: 0886-9383
    Keywords: Generalized inverse ; K-matrix analysis ; P-matrix analysis ; Least squares ; Principal component regression ; Partial least squares ; Continuum regression ; Beer's law ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper consists of two distinct but related parts. In the first part a geometric theory of generalized inverses is presented and a methodology based on this theory is developed and applied to solve the K-matrix and P-matrix forms of Beer's law. It is shown that most currently accepted and practiced methods for solving these forms of Beer's law are just special cases of this geometric theory of generalized inverses. In addition, this geometric theory is used to explain why the current methods work and why they fail.In the second part a general methodology that includes as special cases least squares, principal component regression, partial least squares 1 and 2, continuum regression plus a variety of other described and undescribed methodologies is presented and then applied to solve the P-matrix formulation of Beer's law. This general methodology, like the first, is also geometric in nature and relies on an understanding of projections.The main emphasis of this paper is one of perspective, which, if understood, provides the proper foundation for answering the general but extremely hard and possibly unanswerable question “what is the best method?”.
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  • 15
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    Journal of Chemometrics 7 (1993), S. 195-212 
    ISSN: 0886-9383
    Keywords: Calibration ; Non-linearity ; Principal components ; Stein estimate ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new regression method for non-linear near-infrared spectroscopic data is proposed. The technique is based on a model which is linear in the principal components and simple functions (squares and products) of them. Added variable plots are used to determine which squares and products to incorporate into the model. The regression coefficients are estimated by a Stein estimate which shrinks towards the estimate determined by the first several principal components and the selected non-linear terms. The technique is not computationally intensive and is appropriate for routine predictions of chemical concentrations. The method is tested on three data sets and in all cases gives more accurate predictions than does linear principal components regression.
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  • 16
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    Journal of Chemometrics 7 (1993), S. 227-242 
    ISSN: 0886-9383
    Keywords: Non-linear mapping ; Graphical methods ; SAR ; SPR ; Quality of representation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From a review of the theoretical aspects of non-linear mapping and the different algorithms available in the literature, the methodological and practical problems linked to the use of this multivariate method in structure-activity and structure-property relationship studies are underlined. Useful tools for the graphical display of the outputs and the interpretation of the obtained clusters are presented. Statistical parameters estimating the quality of the graphical representation of each individual are also introduced. An example of application on a data matrix of 37 acaricides described by four physicochemical descriptors (π, F, R, MR) is presented.
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  • 17
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    Journal of Chemometrics 7 (1993), S. 291-304 
    ISSN: 0886-9383
    Keywords: Partial least squares ; Monte Carlo methods ; Cross validation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Partial least squares (PLS) regression is a commonly used statistical technique for performing multivariate calibration, especially in situations where there are more variables than samples. Choosing the number of factors to include in a model is a decision that all users of PLS must make, but is complicated by the large number of empirical tests available. In most instances predictive ability is the most desired property of a PLS model and so interest has centred on making this choice based on an internal validation process. A popular approach is the calculation of a cross-validated r2 to gauge how much variance in the dependent variable can be explained from leave-one-out predictions. Using Monte Carlo simulations for different sizes of data set, the influence of chance effects on the cross-validation process is investigated. The results are presented as tables of critical values which are compared against the values of cross-validated r2 obtained from the user's own data set. This gives a formal test for predictive ability of a PLS model with a given number of dimensions.
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  • 18
    ISSN: 0886-9383
    Keywords: Reaction kinetics ; Initial rate ; Kinetic order ; Response surface modelling ; Canonical analysis ; Organic synthesis ; Optimization ; Reaction mechanisms ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is presented by which it is possible to estimate the initial rate of chemical reactions when the experimental conditions are varied according to a response surface design. The method is intended as a complementary method for analysing data obtained from experiments in synthetic chemistry when the objective is to optimize the yield of the reaction.Data obtained by simulations have been used to develop the method. From the simulated reactions it is shown that sequential analysis of the chemical yield of the reaction makes it possible to estimate models which describe how the parameters of the response surface of the yield vary over time. The derivatives of these time functions of the response surface parameters can be used to define a rate function which describes how the variations in the experimental conditions influence the rate of the reaction.It is shown how such rate functions can be used to afford reasonable estimates of the initial rates of the reaction. The initial reaction rates thus estimated can be used to determine the kinetic order of the reactants and also to provide estimates of the activation energy of the reaction.A thorough discussion of how canonical analysis of the rate function may assist in the elucidation of reaction mechanisms is given.
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  • 19
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    Journal of Chemometrics 7 (1993), S. 427-438 
    ISSN: 0886-9383
    Keywords: Quality control ; Kerosene ; Variable reduction ; Cross-validation ; Variable selection ; Procrustes rotation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper deals with a typical question encountered in all industrial analytical laboratories: are all the tests performed in the laboratory to characterize the final product really necessary? In this work the cross-validation technique, Procrustes rotation techniques and statistical variable selection have been used to reduce the 26 initial British Petroleum and ASTM kerosene specification test to ten ‘essential’ ones. Statistical as well as chemical considerations were used to select the optimum subset of original variables to be retained from all the possible ones.
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  • 20
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    Journal of Chemometrics 7 (1993), S. 453-454 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 21
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    Journal of Chemometrics 7 (1993), S. 527-541 
    ISSN: 0886-9383
    Keywords: Principal component analysis ; Projection pursuit ; Simulated annealing algorithm ; Robust statistics ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Principal component analysis (PCA) is a widely used technique in chemometrics. The classical PCA method is, unfortunately, non-robust, since the variance is adopted as the objective function. In this paper, projection pursuit (PP) is used to carry out PCA with a criterion which is more robust than the variance. In addition, the generalized simulated annealing (GSA) algorithm is introduced as an optimization procedure in the process of PP calculation to guarantee the global optimum. The results for simulated data sets show that PCA via PP is resistant to the deviation of the error distribution from the normal one. The method is especially recommended for use in cases with possible outlier(s) existing in the data.
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  • 22
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    Journal of Chemometrics 7 (1993), S. 45-59 
    ISSN: 0886-9383
    Keywords: Partial least squares ; PLS algorithm ; Kernel ; Multivariate image analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A fast and memory-saving PLS regression algorithm for matrices with large numbers of objects is presented. It is called the kernel algorithm for PLS. Long (meaning having many objects, N) matrices X (N × K) and Y (N × M) are condensed into a small (K × K) square ‘kernel’ matrix XTYYTX of size equal to the number of X-variables. Using this kernel matrix XTYYTX together with the small covariance matrices XTX (K × K), XTY (K × M) and YTY (M × M), it is possible to estimate all necessary parameters for a complete PLS regression solution with some statistical diagnostics. The new developments are presented in equation form. A comparison of consumed floating point operations is given for the kernel and the classical PLS algorithm. As appendices, a condensed matrix algebra version of the kernel algorithm is given together with the MATLAB code.
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  • 23
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    Journal of Chemometrics 7 (1993), S. 77-88 
    ISSN: 0886-9383
    Keywords: Direct trilinear decomposition method ; Curve resolution ; Trilinear data ; Similarity transformation ; Generalized rank annihilation method ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The direct trilinear decomposition method (DTDM) is an algorithm for performing quantitative curve resolution of three-dimensional data that follow the so-called trilinear model, e.g. chromatography-spectroscopy or emission-excitation fluorescence. Under certain coditions complex eigenvalues and eigenvectors emerge when the generalized eigenproblem is solved in DTDM. Previous publications never treated those cases. In this paper we show how similarity transformations can be used to eliminate the imaginary part of the complex eigenvalues and eigenvectors, thereby increasing the usefulness of DTDM in practical applications. The similarity transformation technique was first used by our laboratory to solve the similar problem in the generalized rank annihilation method (GRAM). Because unique elution profiles and spectra can be derived by using data matrices from three or more samples simultaneously, DTDM with similarity transformations is more efficient than GRAM in the case where there are many samples to be investigated.
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  • 24
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    Journal of Chemometrics 7 (1993), S. 143-148 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Journal of Chemometrics 7 (1993), S. 151-151 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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  • 26
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    Journal of Chemometrics 7 (1993), S. 213-222 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 27
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    Journal of Chemometrics 7 (1993) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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  • 28
    ISSN: 0886-9383
    Keywords: Multicomponent analysis ; Factor analysis ; Detection limit ; Local rank ; Zero-component region ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we redefine the term detection limit to embrace the inherent multivariate nature of samples, instrumental measurements and chemometrics resolution procedures. The so-called zero-component regions, i.e. parts with no chemical components eluting, are used as repeated analytical blanks to estimate a statistical multivariate detection limit for determining the number of chemical species in local regions of a single two-way chromatogram or a collection of synchronized one-way chromatograms. For two-way chromatography the detection limit is determined from the distribution of the first eigenvalues obtained from all possible combinations of spectra in the zero-component regions. The number of spectra in each calculation should correspond to the number included in the later examination of the local retention time regions. For one-way chromatography on a collection of samples with similar chemical components at varying concentrations the same procedure is used, with the samples taking the role of the spectra in two-way chromatography. The detection limit can be chosen at various confidence levels depending on whether false positive or negative detection of minor components is most critical. The results obtained from the zero-eigenvalue distribution are more robust than those obtained by a previously developed F-test.
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  • 29
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    Journal of Chemometrics 7 (1993), S. 447-452 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 30
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    Journal of Chemometrics 7 (1993), S. 477-494 
    ISSN: 0886-9383
    Keywords: Three-way principal components analysis ; Core matrix ; Body diagonalization ; Lower and upper bounds ; Simulation ; Soil contamination ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In contrast with conventional PCA, a direct superposition and joint interpretation of loading plots is not possible in three-way PCA, since there may be data variance which is described by unequal components of different modes. The contributions to variance of all possible combinations of components are described in the core matrix. Body diagonalization, which is achieved by appropriate rotation of component matrices, is an essential tool for simplifying the core matrix structure. The maximum degree of body diagonality which may be obtained from such transformations is analysed from both the mathematical and simulation viewpoints. It is shown that, at least in the average case, high degrees can be expected, which makes the procedure reasonable for many practical applications. Furthermore, simulation as well as theoretical derivation show that the success of body diagonality depends on the so-called polarity of the core array. The methodology is illustrated by a three-way data example from environmental chemistry.
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  • 31
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    Journal of Chemometrics 7 (1993), S. 551-557 
    ISSN: 0886-9383
    Keywords: Krylov sequence ; Partial least squares ; Polynomial regression ; Principal component regression ; R2 ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: PLS1 regression is generally viewed as lying in between PCR and OLS regression. Proof is given that the coefficient of determination, R2, for a PLS multivariate calibration model is at least as high as that for a PCR model with the same number of components. It appears that PLS can be linked to a correlation-weighted polynomial regression of a constant response on the eigenvalues of the covariance matrix of the predictor variables.
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  • 32
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    Journal of Chemometrics 7 (1993), S. 1-14 
    ISSN: 0886-9383
    Keywords: Continuum regression ; Dynamic model identification ; Principal component regression ; Partial least squares regression ; Finite impulse response ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of continuum regression (CR) for the identification of finite impulse response (FIR) dynamic models is investigated. CR encompasses the methods of principal component regression (PCR), partial least squares (PLS) and multiple linear regression (MLR). PCR and MLR are at the two extremes of the continuum. In PCR and PLS, cross-validation is used to determine the optimum number of factors or ‘latent variables’ to retain in the regression model. CR allows one to vary the method in addition. Cross-validation then determines both the optimum method and the number of latent variables. The CR ‘prediction error surface’ - a function of the method and number of latent variables - is elucidated. The optimal model is defined as the minimum of this surface. Among the cases studied, the optimal model usually comes from the region of the continuum between PCR and PLS. Few derive from the region between PLS and MLR. It is also demonstrated that FIR models identified by CR have frequency domain properties similar to those identified by PCR.
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  • 33
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    Journal of Chemometrics 7 (1993) 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 34
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    Journal of Chemometrics 7 (1993), S. 117-130 
    ISSN: 0886-9383
    Keywords: Calibration ; Rank annihilation ; Three-way ; Trilinear ; Bilinear ; Non-bilinear ; Net analyte signal ; MS/MS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several multivariate methods are now available for the calibration of second-order or hyphenated instruments (e.g. GC/MS). When applied to bilinear data, it has been shown that calibration can be performed in the presence of unknown interferences - a significant advantage over first-order calibration. In this paper, non-bilinear rank annihilation (NBRA), a method which has the potential of handling, second-order non-bi-linear data, is studied through theoretical analysis and computer simulation. It is found that the second-order advantage can be carried over to non-bilinear data if a property defined as net analyte rank (NAR) holds for the analyte of interest. The net analyte signal (NAS) is defined accordingly for second-order calibration and the analogy to and difference from lower-order calibration are discussed. With NAS, some analytical figures of merit such as signal-to noise ratio, selectivity, sensitivity and limit of determination can be calculated for second order calibration. An application to MS/MS data is also given.
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  • 35
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    Journal of Chemometrics 7 (1993) 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 36
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    Journal of Chemometrics 7 (1993), S. 177-193 
    ISSN: 0886-9383
    Keywords: Multivariate analysis ; Function space ; Coefficient space ; B-splines ; Compression ; PCA ; PLS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general framework for manipulating spectra as functions in traditional multivariate methods such as PCA and PLS is described. The functional representation is very convenient for compression, ensuring smoothness and continuity. There are two fundamentally different types of representations: (a) by functions and (b) by function coefficients. The use of coefficients is the most practical way of analysis.
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  • 37
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 38
    ISSN: 0886-9383
    Keywords: Kalman filter ; Multivariate calibration ; Condition number ; Prediction error ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The usefulness of the Kalman filter as an algorithm for calibration in a real system is shown. Results are compared with classical least squares and pure component calibration. The prediction of four priority pollutant chlorophenols in binary, ternary and quaternary mixtures was also carried out by Kalman filtering. The condition number, standard deviation and prediction error have been employed to choose the most suitable wavelength range. Comparison of the standard error of prediction in the validation set shows significant differences between the evaluated chlorophenols, the best results being obtained with Kalman multivariate calibration.
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  • 39
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    Journal of Chemometrics 7 (1993), S. 255-265 
    ISSN: 0886-9383
    Keywords: Multicomponent calibration ; Non-linearity ; Selectivity ; Wavelength selection ; Graphical diagnostics ; Outliers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Modern scanning infrared reflectance/absorption spectroscopes measure absorptions or reflectance at a sequence of around 1000 wavelengths. Training data may consist of 10-100 carefully designed sample mixtures whose true compositions are either known by formulation or accurately determined by wet chemistry. In future, one wishes to predict the true composition of a newly presented sample from its spectrum. Varying compositions of a mixture of three sugars in water are used for illustration of several different graphical techniques; the spectral measurements here are near-infrared (NIR) absorbances, but there is nothing exclusively infrared about the methodology. Graphs display the adequacy of a linear explanation of absorbance variability at each wavelength by wavelength linearity plots. These highlight regions of the spectrum where non-linearities and interaction effects are substantial. By selecting out these substantially non-linear regions, one can concentrate on linear formulae for prediction with resultant robust linear modelling. Such selections are further aided by plots which identify the component sugar for which each wavelength is most selective. Such plots offer rather natural pre-screening as an alternative or supplement to the wavelength selection method of Brown.We also display prediction diagnostics (R, Rx) which on a sample-by-sample basis may diagnose a particularly unusual presented spectrum. These diagnostics are shown to have predictive import for a validation data set.
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  • 40
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    Journal of Chemometrics 7 (1993), S. 305-340 
    ISSN: 0886-9383
    Keywords: Stem & leaf display ; Histogram ; Boxplot ; Quantile plot ; Scatterplot ; Regression ; Smoothing ; 3D rotation ; Scatterplot matrix ; OMEGA strategy ; Dimension reduction ; Stability of structure ; Resampling ; Interpretation of structure ; Prediction models ; Variables selection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Exploratory data analysis (EDA) is a toolbox of data manipulation methods for looking at data to see what they seem to say, i.e. one tries to let the data speak for themselves. In this way there is hope that the data will lead to indications about ‘models’ of relationships not expected a priori. In this respect EDA is a pre-step to confirmatory data analysis which delivers measures of how adequate a model is. In this tutorial the focus is on multivariate exploratory data analysis for quantitative data using linear methods for dimension reduction and prediction. Purely graphical multivariate tools such as 3D rotation and scatterplot matrices are discussed after having introduced the univariate and bivariate tools on which they are based. The main tasks of multivariate exploratory data analysis are identified as ‘search for structure’ by dimension reduction and ‘model selection’ by comparing predictive power. Resampling is used to support validity, and variables selection to improve interpretability.
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  • 41
    ISSN: 0886-9383
    Keywords: Curve resolution ; Multicomponent analysis ; Latent projections ; Local factor analysis ; Chlorophyll degradation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-performance liquid chromatography with diode array detection (HPLC--DAD) is used to characterize mixtures from chlorophyll a degradation experiments. Overlapping chromatographic peaks are resolved by means of the heuristic evolving latent projections (HELP) method. The HELP method is a self-modelling curve resolution method. No assumptions are made about spectral and/or chromatographic peak shape. In the first step the method establishes the real noise level in the data by use of the so-called zero-component regions. This information is used to reveal selective chromatographic information and the number of chemical species at every retention time in unresolved chromatographic peaks. Utilising the selective chromatographic regions in combination with the zero-concentration windows, unique resolution into concentration profiles and spectra of the pure chemical species is accomplished. HPLC-DAD data from six chlorophyll a degradation experiments were analysed. Consistent results were obtained even with very similar spectra for six or seven overlapping chemical components.
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  • 42
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    Journal of Chemometrics 7 (1993), S. 99-115 
    ISSN: 0886-9383
    Keywords: Classification ; Appreciation function ; Regularized discriminant analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Regularized discriminant analysis has proven to be a most effective classifier for problems where traditional classifiers fail because of a lack of sufficient training samples, as is often the case in highdimensional settings. However, it has been shown that the model selection procedure of regularized discriminant analysis, determining the degree of regularization, has some deficiencies associated with it. We propose a modified model selection procedure base on a new appreciation function. By means of an extensive simulation it was shown that the new model selection procedure performs better than the original one. We also propose that one of the control parameters of regularized discriminant analysis be allowed to take on negative values. This extension leads to an improved performance in certain situations. The results are confirmed using two chemical data sets.
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    Journal of Chemometrics 7 (1993), S. 149-150 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 44
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    Journal of Chemometrics 7 (1993), S. 165-176 
    ISSN: 0886-9383
    Keywords: Measurement error ; Outliers ; Environmental ; Quality control ; Multivariate kurtosis ; Generalized distance ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Environmental data are usually multivariate, with the variables conforming to some correlation structure. Occasionally, measurements which do not conform in structure or magnitude may occur in one or more variables. It is important (1) to characterize these discordancies in terms of the disturbed variables and the direction and magnitude of the anomalous error and (2) to associate each discordant observation with a specific cause of measurement error in order to prevent further mismeasurement. We describe a procedure for identifying suspected causes of discordant observations in otherwise multinormal data sets. Variables are assigned to groups, each of which is associated with a specific cause of measurement error. Discordant observations are identified with the generalized distance test or the multivariate kurtosis test. Suspected causes of measurement error are identified by repeating the tests with one of the groups of variables omitted in each analysis. The procedures are evaluated with simulated data sets having a correlation structure similar to that of a large environmental data set.
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    Journal of Chemometrics 7 (1993), S. 393-425 
    ISSN: 0886-9383
    Keywords: Preprocessing ; Closure ; Normalization ; Ratioing ; Constant sum transformation ; Constant length transformation ; Maximum value transformation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The geometric properties of three common object-preprocessing transformations (constant sum, or closure; constant length, or normalization; and maximum value, or ratioing) are investigated. An argument is made for using absolute values in the constant sum and maximum value transformations. In general, each transformation distorts the shape and dimensionality of patterns in the data: transformed data lie on (C-1)-dimensional surfaces in the original C-dimensional space. A data set that has been closed by one of these transformations can be reopened if a vector containing the constant sums, constant lengths or maximum values of the original objects was retained. Transformed data sets may be freely interconverted among these three transformations without the loss of information.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 47
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    Journal of Chemometrics 7 (1993), S. 455-475 
    ISSN: 0886-9383
    Keywords: Biological activity ; Cross-validation ; Exchangeability ; Molecular descriptors ; Prediction ; Relationship ; Structure ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The two parts of this paper form a critique of a variety of statistical techniques of actual or potential use in quantitative structure-activity relationship (QSAR) studies and related fields. Part I explores the statistical thinking that is needed to underpin those techniques. Emphasis as placed on (a) the role of ‘exchangeability’ as an alternative to unrealistic statistical modelling and (b) the use of cross-validation to limit self-deception in the use of any particular technique. The problem of the almost unlimited range of molecular descriptors is seriously addressed. (Part II provides a concise critical review of methods-some well-established and some new.)
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    Journal of Chemometrics 7 (1993), S. 543-550 
    ISSN: 0886-9383
    Keywords: Fragment occurrence data ; Molecular similarity ; Similarity searching ; Standardization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substructural fragment occurrence data are widely used as the basis for measures of inter-molecular structural similarity. This paper investigates the effect of standardization on the effectiveness of such measures using eight data sets for which both structural and biological activity data are available. Eight different standardization methods are studied and it is shown that there is no significant difference in the effectivenesses of the various methods; accordingly, any of them can be used for the calculation of intermolecular structural similarity.
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    Journal of High Resolution Chromatography 16 (1993), S. 27-30 
    ISSN: 0935-6304
    Keywords: Capillary GC ; Solid phase extraction ; Cold on-column injection ; Antiepileptic drugs ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple and quick gas chromatographic method has been developed for the determination of up to six commonly used antiepileptic drugs in human serum. The antiepileptics are isolated from serum by solid phase extraction on to a reversed phase sorbent and recovered with ethyl acetate as eluent. The ethyl acetate eluate is suitable for direct on-column injection on to a phenyl methyl siloxane capillary column; hydrogen is used as carrier gas and the compounds are separated with a two-ramp temperature program. Detection is by FID.The reproducibility of the method varies between 2 and 6% RSD, depending on the drug and the level analyzed; limits of detection were found to be 14-51 pg and minimum assayed concentrations in serum were between 14 and 51 ng/ml.
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    Journal of High Resolution Chromatography 16 (1993), S. 18-26 
    ISSN: 0935-6304
    Keywords: Column liquid Chromatography ; Serially coupled columns ; Selectivity tuning by changing the flow rate ; Stationary phases of different selectivity ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tuning of selectivity by changing the flow rate has been investigated in HPLC: two columns with different retention characteristics were coupled in series via a T-piece and the relative retention of components chromatographed on the system were changed by varying the individual flow rates in the coupled columns. The flow rate alteration was performed by adding a second flow after the first column. The flow rate ratio necessary for optimum resolution can be easily calculated on the basis of the capacity factors measured on the individual columns. The performance of this method for adjusting selectivity has been demonstrated by using different column combinations to separate several mixtures containing chlorophenols, nitroaromatic compounds, and aromatic hydrocarbons.
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  • 51
    ISSN: 0935-6304
    Keywords: On-column injection ; On-line injection ; Large (100 μ) injections ; Precision ; Linearity ; Carry-over ; Discrimination ; Activity ; Polar compounds ; High boiling compounds ; Environmental analyses ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This report describes an on-line capillary GC injection system which enables on-column injection of a hundred or more microliters, and yields separations comparable with those obtained from on-column injection of 1-2 microliters of solutions a hundred times more concentrated. Precision, carry-over, linearity, and discrimination are comparable with those of classical sample-introduction techniques. A selection of polar and high boiling compounds has been examined, and excellent peak shapes obtained for hundreds of injections. Initial results indicate that maintenance and long-term reproducibility will also be comparable with those of classical techniques.The instrument utilizes a version of the large volume on-column injector with solvent diversion described in an earlier communication, with the addition of a method for independent heating of the retention gap. This modification reduces the effects of activity in the retention gap and improves the capability of the technology to handle complex mixtures. It also increases reliability and system lifetime, fits readily into most GC ovens, is easily automated, and should be compatible with all capillary GC detectors.
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  • 52
    ISSN: 0935-6304
    Keywords: GC-AED ; Sulfur ; FCC gasoline ; Compound-independent calibration ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The identification and quantification of sulfur-containing compounds in gasoline has become an area of interest because of impending legislation regulating total sulfur levels in these fuels. To study the effects of catalyst type and catalytic conditions on gasoline sulfur distribution, a method has been developed employing both the compound-independent and element-specific response of the atomic emission detector (AED). Calibration and quantification can be accomplished even where standards are not available, owing to the nature of the AED response.Compounds were separated on a thick film polydimethylsiloxane column. An external calibration curve was applied to the area responses of individual sulfur components in the sulfur chromatogram, and the concentrations of each were calculated. Summation of these sulfur concentrations over the gasoline range yields the total sulfur content of the gasoline.The method is applicable to the determination of these compounds in raw crude oils, finished gasolines, fluid cracking catalyst (FCC) unit gasolines, and fluid catalytic cracking “model” compound studies. A prefractionating column was employed to remove heavy (〉C13) materials; prefractionation is not, however, necessary for distilled or commercial gasoline samples. Detection limits, linearity, detector stability, and accuracy are discussed.
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    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 54
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    Journal of High Resolution Chromatography 16 (1993), S. 46-51 
    ISSN: 0935-6304
    Keywords: Capillary GC ; Retention time prediction ; Programmed temperature ; Linear programming ; Chlorobenzenes ; Iterative procedure ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Retention times in linear temperature programmed gas chromatography on narrow bore and megabore capillary columns have been calculated from experimental retention times measured at three isothermal temperatures: an iterative procedure performed by BASIC programs was used to obtain the values of the constants enabling the calculation of the programmed temperature retention times. Different methods of calculation have been compared.
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    Journal of High Resolution Chromatography 16 (1993), S. 31-38 
    ISSN: 0935-6304
    Keywords: Efficiency, erosion of ; Non-uniform chromatography ; Linear chromatography ; Plate height, uniform ; Solute velocity ; Capacity ratio, variation ; SFC pressure drop ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In linear chromatography (i.e. chromatography performed in the absence of sample overloading), when the plate height of a column is roughly uniform along its length, variations in the velocities of solutes are the only possible causes of erosion of efficiency. The sources of these variations (variations in capacity ratio and in the density of the mobile phase, etc.) play no direct role in the erosion of efficiency except through their effect on solute velocities. In other words, what eventually causes the erosion of efficiency is merely variation in the time required for solutes to traverse equally small segments of a column. Significant erosion can only arise from abrupt and deep deceleration of solutes in one or several relatively small segments of a column.If erosion of efficiency caused by pressure gradients in linear SFC is to be large, the depth and the sharpness of the deceleration of a solute must go beyond that hitherto confirmed experimentally. Many relevant examples are analyzed graphically.
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    Journal of High Resolution Chromatography 16 (1993), S. 175-181 
    ISSN: 0935-6304
    Keywords: Enantioselective gas chromatography ; 2,6-di-O-methyl-3-O-pentyl-β- and y-cyclodextrins ; α and β hydroxy acids ; Branched carboxylic acids ; Non-steroidal anti-inflammatory drugs ; Abscisic Acid ; Epoxides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The wide range of application of 2,6-di-O-methyl-3-O-pentyl-β-and y-cyclodextrins is demonstrated by the resolution of the enantiomers of the methyl esters of chiral carboxylic acids: α and β hydroxy acids with up to 18 carbon atoms, hydroxy di- and tricarboxylic acids, and alkyl/aryl-substituted carboxylic acid methyl esters, including the plant hormone abscisic acid, insect juvenile hormones, and some non-steroidal anti-inflammatory drugs can be resolved with generally large separation factors. The new cyclodextrin derivatives also exhibit high selectivity for epoxides.
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    Journal of High Resolution Chromatography 16 (1993), S. 192-193 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 16 (1993), S. 188-191 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Thermostable WCOT columns ; PLOT columns ; Stainless steel ; Silicon layer for deactivation ; Simulated distillation ; PNA analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A layer of elemental silicon has been deposited on the surface of stainless steel tubing by means of chemical vapor deposition (CVD). Two kinds of capillary column were prepared from the deactivated tubing: cross-linked, silanol-terminated polydime-thylsiloxane wall coated open tubular (WCOT) columns and molecular sieve 13X porous layer open tubular (PLOT) columns. Unlike fused silica capillary columns, stainless steel WCOT and PLOT columns can be operated at temperatures in excess of 400°C. High temperature simulated distillation has been performed successfully with a macro bore WCOT column and rapid PNA (paraffin, naphthene, and aromatic) analysis with a multidimensional gas solid chromatographic (GSC) system using PLOT columns.
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    Journal of High Resolution Chromatography 16 (1993), S. 193-193 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 16 (1993), S. 194-195 
    ISSN: 0935-6304
    Keywords: Open-tubular liquid chromatography ; Liquid-liquid chromatography ; Electrochemical detection ; Phenols ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    ISSN: 0935-6304
    Keywords: Supercritical fluid chromatography ; Supercritical fluid extraction ; Poly(vinyl chloride) ; Dimethyltin mercaptide ; Formic acid ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 16 (1993), S. 52-52 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 16 (1993), S. 53-55 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Plant extract ; Photochemical degradation ; Insecticides ; Volatile compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 16 (1993), S. 55-57 
    ISSN: 0935-6304
    Keywords: Liquid chromatography, HPLC ; Cyanopropyl phase ; Simple lipids ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 16 (1993), S. 57-59 
    ISSN: 0935-6304
    Keywords: HPLC ; Fluorescence emission detection ; Specific dual detection ; Amperometric oxidation detection ; Polymeric reagent ; Derivatization ; Aliphatic amines ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 16 (1993), S. 59-61 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Glass capillary micropacked columns ; SPE sorbents ; Aliphatic hydrocarbons ; Aromatic hydrocarbons ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 16 (1993), S. 65-66 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 16 (1993), S. 73-84 
    ISSN: 0935-6304
    Keywords: Sample introduction ; Injection ; Supercritical fluid chromatography ; Supercritical fluid extraction ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New strategies for sample introduction in supercritical fluid chromatography are reviewed. Both open tubular and packed column systems are examined as the injection demands of each column type are addressed. In addition to advances made in solvent injection methods, supercritical fluid extraction (SFE) is discussed as a solventless injection technique for supercritical fluid chromatography.
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  • 69
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    Journal of High Resolution Chromatography 16 (1993), S. 85-89 
    ISSN: 0935-6304
    Keywords: Fullerenes ; Liquid chromatography ; Mass Spectrometry ; LC-MS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fullerene-rich soot generated by resistive heating of graphite has been gently extracted with toluene, in order to remove some C60 and C70 compounds, followed by extraction with boiling 1,2,4-trichlorobenzene at 214°C. After filtration and removal of the solvent, the residue was re-dissolved in dichloromethane and characterized by non-aqueous reversed phase liquid chromatography coupled on-line with atmospheric pressure chemical ionization mass spectrometry. Several novel fullerenes were detected, including C72, C80, C86, and C88 as well as other fullerenes up to C108 and higher. The results indicate that chromatographic separation of large fullerene molecules can be achieved with low boiling point solvents and conventional liquid chromatographic techniques.
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  • 70
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    Journal of High Resolution Chromatography 16 (1993), S. 95-100 
    ISSN: 0935-6304
    Keywords: Capillary GC ; Biscyanopropyl siloxane phases ; Temperature program optimization ; Computer simulation (Drylab GC) ; Fatty acid methyl esters ; Electronic pressure control ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The selectivity of capillary columns coated with biscyanopropyl siloxane stationary phases for the separation of fatty acid methyl esters has been optimized by means of computer-assisted column temperature optimization software. Temperature programming rates yielding the highest resolution in the shortest analysis time were selected for split, splitless, and on-column injection operated in the constant pressure and pressure programmed modes.
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  • 71
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    Journal of High Resolution Chromatography 16 (1993), S. 90-94 
    ISSN: 0935-6304
    Keywords: On-column injection ; Large (100 μl) injections ; Heated retention gap ; Sample preparation ; Extraction efficiency ; Linearity ; Limit of detection ; Polynuclear aromatic hydrocarbons (PAHs) ; Industrial Waste ; Water analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An automated large volume on-column injection technique for capillary gas chromatography (GC) with solvent divert and heated retention gap technology has been utilized to determine polynuclear aromatic hydrocarbons (PAHs) in samples of industrial plant process water. Injecting large sample volumes on-column enabled the sample preparation procedure to be simplified and provided a fast, labor-saving technique for screening water samples. Diverting approximately 95% of the solvent away from the analytical column and the detector enabled chromatography to reflect classical capillary loading and detector conditions.Simplifications include significant reduction of sample and eluent volumes used during extraction and the elimination of Kuderna-Danish evaporative concentration. System performance, such as linearity and limit of detection, were evaluated for selected PAHs. Spiked water samples were prepared in the lower μ/L range to determine extraction efficiency. Results are compared with those obtained by a reputable contract laboratory following EPA Method 625.
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  • 72
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    Journal of High Resolution Chromatography 16 (1993), S. 101-105 
    ISSN: 0935-6304
    Keywords: Enantioselective LC (GC) analysis ; β-Cyclodextrin chiral LC-phase ; Heptakis(2,3-di-O-methyl-6-TBDMS)-β-cyclodextrin ; Chiral dihydrofuranones ; Enantiomer eluate sniffing ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The odor impression of the pure enantiomers of various chiral dihydrofuranones which are important flavor compounds has been evaluated by sniffing the well separated optical antipodes in the GC eluate from heptakis(2,3-di-O-methyl-6-TBDMS)-β-cyclodextrin as the chiral phase for capillary gas chromato-graphic separation. Liquid chromatographic separation has been achieved by the use of bonded β-cyclodextrin as the chiral stationary phase and methanol-water as eluent. Enantiomer separation in the latter was improved by addition of triethylammonium acetate to the eluent.
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  • 73
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    Journal of High Resolution Chromatography 16 (1993), S. 116-119 
    ISSN: 0935-6304
    Keywords: Carbon layer open tubular (CLOT) columns ; Adsorption/partition separation mechanism ; Van Deemter curves ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Capillary columns coated with Carbopack materials, which provide separation by a mixed partition/adsorption mechanism or by adsorption alone, have recently been developed. The reproducibility of the columns is demonstrated and applications shown in which they provide separations which are either unique or are faster than can be achieved with the wall coated open tubular capillary columns currently available.
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    Journal of High Resolution Chromatography 16 (1993), S. 113-115 
    ISSN: 0935-6304
    Keywords: Capillary GC ; GC-MS ; Headspace ; Milk ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Twenty compounds have been determined by GC-MS in polystyrene used for milk packaging. The major components identified in milk were styrene and its dimer at concentrations of 13 and 43 mg/kg, respectively. The detection limit for styrene by the equilibrium headspace method was 0.29 mg/kg. Another method used to determine the concentration of styrene and its dimer in milk was the use of acetone to precipitate the proteins and extract both the fat and the residues from the plastic packaging. The solution obtained was then directly injected into the GC. The detection limits were found to be 0.16 mg/kg for styrene and 0.28 mg/kg for the dimer. The solution injection method thus proved to be much more sensitive.
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    Journal of High Resolution Chromatography 16 (1993), S. 120-120 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Journal of High Resolution Chromatography 16 (1993), S. 258-261 
    ISSN: 0935-6304
    Keywords: Nomenclature ; Chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The background of the new Unified Nomenclature for Chromatography just accepted by the International Union of Pure and Applied Chemistry (IUPAC) is explained and selected highlights of the new rules are elaborated.
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    Journal of High Resolution Chromatography 16 (1993), S. 262-262 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 16 (1993) 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 16 (1993), S. 275-278 
    ISSN: 0935-6304
    Keywords: Element-specific GC detection ; Spectrometric detection ; Microwave-induced plasma ; Detector instability ; Solvent effect on detector stability ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Capillary gas chromatography coupled to microwave-inducedplasma detection furnishes sensitivity adequate for trace analysis when the signal is monitored at a carbon emission line. Work performed with one of these systems at high electronic gain for the carbon signal has revealed solvent band widths in excess of four minutes; these impeded quantification of peaks eluting after the solvent. This report discusses two phenomena which could be related to the unexpected intensity of this solvent response: photomultiplier tube saturation and carbon deposits in the quartz plasma discharge tube.
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    Journal of High Resolution Chromatography 16 (1993), S. 121-122 
    ISSN: 0935-6304
    Keywords: Sample liquid pulled out of syringe needle ; Accuracy of sample volume ; On-column injection ; Speed of injection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 16 (1993), S. 123-125 
    ISSN: 0935-6304
    Keywords: Sex pheromone ; Isomeric identification ; Capillary gas chromatography ; Mass spectrometry ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 82
    ISSN: 0935-6304
    Keywords: Capillary GC ; Substituted anilines ; Phenylurea herbicides ; Nitrogen selective detector (NPD) ; Water analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 83
    ISSN: 0935-6304
    Keywords: HPLC ; Stationary phase ; Internal surface reversed phase (ISRP) ; One-step clean-up ; Human milk ; PCDDs ; PCDFs ; PCBs ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 16 (1993), S. 130-134 
    ISSN: 0935-6304
    Keywords: Supercritical fluid chromatography ; Packed columns ; Modifiers ; Formic acid ; Formamide ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 16 (1993), S. 135-136 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 16 (1993), S. 148-152 
    ISSN: 0935-6304
    Keywords: On-line SFE-GC ; Polychlorinated biphenyls ; Human milk ; Human blood serum ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On-line coupled supercritical fluid extraction and gas chromatography (SFE-GC) has been utilized for the determination of PCBs and other organochlorine compounds in human milk and blood serum. The procedure involved preconcentration of the sample on C18-silica sorbent in an extraction cell: after precipitation of the proteins up to 20 ml of human milk was concentrated on 0.5 g of sorbent. Serum (up to 5 ml) was applied to the C18 material without pretreatment. Basic alumina was utilized as a selective adsorbent for lipids in the on-line SFE-GC system. The method was used to analyze milk and serum spiked with 0.5 and 10 ng of Aroclor 1260 and the results compared with those obtained by liquid-liquid extraction of serum.
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    Journal of High Resolution Chromatography 16 (1993), S. 289-298 
    ISSN: 0935-6304
    Keywords: Enantioselective GC ; Polysiloxane-anchored cyclodextrin stationary phase ; Chirasil-Dex-TFA ; Immobilized 2,6-di-O-alkyl-3-O-acyl-cyclodextrin ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heptakis(2,6-di-O-methyl-3-O-trifluoroacetyl)-†-cyclodextrin has been chemically bonded to a polydimethylsiloxane via an octamethylene spacer and subsequently immobilized on to the surface of fused silica capillaries, the first time a cyclodextrin derivative with mixed substituents has been immobilized in this way. The enantioselectivity of the new chiral stationary phase has been investigated as a function of the cyclodextrin content. It was found to be higher than that reported for heptakis (2,6-di-O-methyl-3-O-trifluoroacetyl)-†-cyclodextrin or hepta-kis(2,6-di-O-methyl-3-O-acetyl)-†-cyclodextrin dissolved in polysiloxane (e.g. OV-1701). The degree of immobilization was over 90 %. The temperature stability is, however, inferior to that of Chirasil-Dex (a permethylated cyclodextrin): the maximum operating temperature is approximately 200 °C.
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    Journal of High Resolution Chromatography 16 (1993), S. 328-328 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 16 (1993), S. 312-323 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 90
    ISSN: 0935-6304
    Keywords: Capillary electrophoresis ; Isotachophoresis preconcentration ; Nonaqueous buffer ; Metabolism ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 16 (1993), S. 157-160 
    ISSN: 0935-6304
    Keywords: HPLC ; Inductively coupled plasma MS ; Coal extracts ; Gallium porphyrins ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The HPLC-ICPMS determination of gallium porphyrins in various coal extracts is described. The HPLC-ICPMS results are compared with results obtained by HPLC-UV/VIS. The presence of gallium has been confirmed in all the porphyrin macrocycles.
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  • 92
    ISSN: 0935-6304
    Keywords: Capillary GC ; Mycobacterium ; Single colony ; Trimethylsulfonium hydroxide (TMSH) ; Fatty acid methyl esters (FAMEs) ; Mycolic acid cleavage products (MACPs) ; Secondary alcohols ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Trimethylsulfonium hydroxide (TMSH) reproducibly converts fatty acids bound in, e.g., biomolecules such as phospholipids and/or glycerides, into the corresponding fatty acid methyl esters (FAMEs). The transesterification can be performed at room temperature in a fast single step reaction. Surprisingly, secondary alcohols and mycolic acid cleavage products (MACPs) are also released from mycobacteria under these conditions.The complex reaction mixtures containing FAMEs, MACPs, and secondary alcohols can easily be separated by high resolution temperature-programmed capillary GC. Different species of mycobacteria give rise to characteristic chromatographic patterns and the amount of lipids from a single colony of mycobacteria is sufficient for reliable identification of the bacteria. The profiles of the chromatograms match well those obtained from other sample preparation techniques.The TMSH method of identification of mycobacteria from the patterns of the gas chromatograms is faster and more sensitive than conventional methods, which also involve transesterification. The identification of mycobacterial species by microbiological culture techniques is difficult to perform and requires several weeks.
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    Journal of High Resolution Chromatography 16 (1993), S. 182-187 
    ISSN: 0935-6304
    Keywords: PTV injector ; Liner design ; On-line LC-GC interfacing ; Large volume sample introduction ; Programmed temperature injection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Programmed temperature sample introduction is an attractive technique both for the introduction of large volumes of dilute samples in capillary gas chromatography and for LC-GC interfacing.In this study a new type of liner containing a porous bed of sintered glass is introduced and evaluated. Solute recoveries achieved with this liner are compared with those obtained from liners packed with Tenax TA and Thermotrap TA. An open liner containing baffles and a small plug of silanized glass wool in its upper section was used as a reference.The maximum speed of sample introduction allowable using the new liner is ca one order of magnitude higher than for the standard liner. For similar liner operating conditions the trapping efficiency is substantially improved: at a liner temperature of -30°C components with a volatility lower than or equal to that of n-tridecane are trapped quantitatively.Liners packed with trapping materials such as Tenax TA or Thermotrap TA also provide significantly improved trapping efficiencies, even when used at relatively high temperatures.
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  • 94
    ISSN: 0935-6304
    Keywords: Supercritical fluid extraction, SFE ; Complexation ; High temperature capillary GC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It has been demonstrated that calcium montanate (a mixture of aliphatic hydrocarbons, fatty acid esters of C28-C32 acids, the calcium salts of these fatty acids, and the acids themselves) can be selectively extracted with supercritical fluids. By use of carbon dioxide, carbon dioxide containing 10% methanol, and carbon dioxide containing 10% methanol and citric acid (as a further additive), the various compound classes could be isolated with high selectivity. The addition of citric acid results in the complexation of Ca2+ and the simultaneous formation of the free fatty acids, which are soluble in the extractant.
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    Journal of High Resolution Chromatography 16 (1993), S. 738-740 
    ISSN: 0935-6304
    Keywords: GC-MS ; Vitamin K1(20) ; Phylloquinone ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 16 (1993), S. 741-741 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 16 (1993), S. 685-685 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 16 (1993), S. 62-64 
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    Keywords: Capillary electrophoresis ; Hollow fiber ; Polypropylene ; Capillary dynamic coating ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 16 (1993), S. 69-69 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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