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  • Analytical Chemistry and Spectroscopy  (6,520)
  • Occupational Health and Environmental Toxicology
  • Wiley-Blackwell  (7,059)
  • Annual Reviews
  • 1995-1999  (2,518)
  • 1980-1984  (4,541)
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  • Wiley-Blackwell  (7,059)
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  • 1
    Electronic Resource
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    Journal of Chemometrics 9 (1995), S. 197-209 
    ISSN: 0886-9383
    Keywords: proficiency test ; true value ; homogeneity robust statistic ; standard ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Profficiency tests raise two types of problems: (i) the homogeneity of a sample must be carefully checked before using it as a reference material; (ii) it is necessary to define a conventional reference value (RV) in order to rank participants. Since these topics are poorly addressed in the literature, a reference material was specially prepared in order to propose a procedure for verifying homogeneity and to establish whether the algorithms classically used to compute the conventional true value have an influence on the conclusion of the test.The homogeneity of the sample was not perfect and univariate and multivariate techniques were used to demonstrate some analytes can be suspected as heterogeneous. However, this was considered adequate for introducing the sample in a large proficiency test organized between four laboratory associations which regularly perform such tests. Altogether more than 3000 measurements were collected and eight algorithms were applied to compute the RV on 14 analytes. Thus is was possible to demonstrate that some of these algorithms are better adapted than others. It is also obvious that some analytes are better suited to proficiency testing.It can be concluded from this work that some effort towards standardization would be profitable to check homogeneity or to compute the RV, especially since the economic weight of proficiency testing is becoming even more important with the development of certification accreditation.
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  • 2
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    Journal of Chemometrics 9 (1995) 
    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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    Journal of Chemometrics 9 (1995), S. 451-457 
    ISSN: 0886-9383
    Keywords: non-linear regression ; optimization ; robust methods ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several robust regression methods, including a new proposal, are described and their properties discussed. Resistance to various types of outliers and non-normality is demonstrated. The techniques are applied to non-linear regression models from chemical kinetics and calibration. Optimization of the types of objective functions encountered when applying robust regression is considered.
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  • 4
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    Journal of Chemometrics 9 (1995), S. 471-481 
    ISSN: 0886-9383
    Keywords: batch prediction ; continuum regression ; multivariate calibration ; sequential prediction ; simultaneous prediction ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In analytical chemistry a single fitted calibration model is used repeatedly to predict the level of the analyte of interest for the specimens comprising the prediction set. Unlike the calibration (or training) set, which is often limited in size, the prediction set can be very large.In the case of multivariate calibration a number of methods such as PLS and PCR are commonly used to construct the calibration model. The set of instrumental measurements and the reference analyte level are available for each specimen in the calibration set. For specimens in the prediction set, only the instrumental measurements are available, since the problem is to predict the analyte level for these specimens. It is not widely recognized that predictions of the analyte levels for individual specimens can be improved by utilizing seemingly unrelated information from the instrumental measurements associated with the other members of the prediction set. In the case of PCR there exists a very straightforward procedure for doing this. A description of the various sources of prediction errors is provided to explain the ability of PCR to utilize this additional information. The use of PCR in this context is illustrated with both a synthetic and a real example.
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  • 5
  • 6
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    Journal of Chemometrics 9 (1995), S. 21-29 
    ISSN: 0886-9383
    Keywords: Near-infrared absorbance ; Partial least squares ; Principal component regression ; Root-mean-square error of prediction ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of principal component regression (PCR) as a multivariate calibration method has been discussed by a number of authors. In most situations principal components are included in the regression model in sequence based on the variances of the components, and the principal components with small variances are rarely used in regression. As pointed out by some authors, a low variance for a component does not necessarily imply that the corresponding component is unimportant, especially when prediction is of primary interest. In this paper we investigate a different version of PCR, correlation principal component regression (CPCR). In CPCR the importance of principal components in terms of predicting the response variable is used as a basis for the inclusion of principal components in the regression model. Two typical examples arising from calibrating near-infrared (NIR) instruments are discussed for the comparison of the two different versions of PCR along with partial least squares (PLS), a commonly used regression approach in NIR analysis. In both examples the three methods show similar optimal prediction ability, but CPCR performs better than standard PCR and PLS in terms of the number of components needed to achieve the optimal prediction ability. Similar results are also seen in other NIR examples.
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  • 7
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    Journal of Chemometrics 9 (1995), S. i 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 8
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    Journal of Chemometrics 9 (1995), S. 137-138 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 9
    ISSN: 0886-9383
    Keywords: pattern recognition ; infrared spectra ; factor analysis ; maximum likelihood method ; entropy of information ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The spectral region from 700 to 3600 cm-1 is subdivided into several wave number intervals. The peaks in each interval are summarized by means of three encoding algorithms. Using a factor model of kcommon factors, the total extractable variacnce (com) of a given set of intervals is calculated and correlated with the redundancy of information in all these intervals. The value of com is verified by analysis of the factor loadings aik (factor pattern). Finally, the information content of some chosen sets of intervals coded by the three selected feature algorithms will be correlated to the probability of information flow through a serial-parallel network. The encoding using only wave numbers was found to be the most effective.
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  • 10
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    Journal of Chemometrics 9 (1995), S. 211-221 
    ISSN: 0886-9383
    Keywords: diagnostics statistics ; QSAR ; MASCA ; principal component regression ; non-least squares regression ; types of multicollincarity ; flagged observations ; influential points ; high-leverage points ; outliers ; extra-carrier points ; random perturbation ; cluster correalation ; resampling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The formal application of a Hansch analysis to a series of 3-quinuclidinyl benzylates (QNBs) led to a ‘statistically significant’ QSAR equation. In contrast, the application of the MASCA model has shown that the design matrix is unsuitable for each QSAR analysis: one sample member is an outlier but not a high-leverage or influential point; another one is an influential point, a high-leverage point and an extra-carrier point. The regressors of the design matrix are multicollinear without predictive model power. The result of such flagged observation and this type of multicollinearity is a multiple cluster correlation. The QNB series is a good example for ‘sampling artifacts’ where no practically important but artificial QSARs can be found.
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  • 11
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    Journal of Chemometrics 9 (1995), S. 230-231 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 12
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    Journal of Chemometrics 9 (1995), S. 239-262 
    ISSN: 0886-9383
    Keywords: industrial experimentation ; parameter design ; quality by design ; robust design ; Taguchi method ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aim of this paper is to present a simple structured review of the different approaches to robust process design to clarify their similarities and dissimilarities. It is primarily written for practitioners who wish to understand and compare the main ideas of each approach and to apply them to their work. Two examples are used to illustrate the different approaches and their corresponding data analysis strategies: the first one is a constructed example on a pigment kneading process and the second one is real example dealing with the validation of an HPLC method. A comparison of the different approaches is provided and some practical recommendations are formulated.
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  • 13
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    Journal of Chemometrics 9 (1995), S. 323-326 
    ISSN: 0886-9383
    Keywords: partial least squares ; biased regression ; ordinary least squares ; minimum length least squares ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An algebraic proof is given that in partial least squares (PLS) regression the Euclidean length of the estimator is shrunk in comparison with the ordinary least squares estimator or with PLS estimators based on a larger number of dimensions.
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  • 14
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    Journal of Chemometrics 9 (1995) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 15
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    Journal of Chemometrics 9 (1995), S. 363-372 
    ISSN: 0886-9383
    Keywords: PLS regression ; orthogonal expansion ; optimization ; Lagrange multipliers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple iteration algorithm that is faster and less memory-intensive than the NIPALS iteration algorithm for PLS regression is presented. The iteration algorithm is obtained by treating the orthogonal expansion or decomposition of a matrix X as an extremum problem subject to normalization and orthogonality constraint conditions and then solving the problem by use of the method of Lagrange multipliers. The main idea in this method is to find the transformation vector r. The latent variable t is expressed exactly as the linear combination of X-variables with the vector r so that the final regression coefficients can be conveniently provided. In the algorithm the recursion of the orthogonal projection is needed, which is derived by use of a matrix inverse formula. Algorithms are established from the equation for calculating the vector r that are suitable for dealing with three cases of large data sets. The first case is when the number of objects is very large, the number of variables is relatively small and the number of Y-variables is equal to or greater than the number of X-variables. The second case is when the number of objects is very large, the number of variables is relatively small and the number of X-variables is greater than the number of Y-variables. The last case is when the number of variables, either X- or Y-variables, or both, is very large and the number of objects is small.
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  • 16
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    Journal of Chemometrics 9 (1995), S. 423-430 
    ISSN: 0886-9383
    Keywords: PLS ; neural network ; training ; interpretable ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This communication describes the combination of a feedforward neural network (NN) with one hidden neuron and partial least squares (PLS) regression. Through training of the neural network with an algorithm that is a combination of a modified simplex, PLS and certain numerical restrictions, one gains an NN solution that has several feasible properties: (i) as in PLS the solution is qualitatively interpretable; (ii) it works faster than or comparably with ordinary training algorithms for neural networks; (iii) it contains the linear solution as a limiting case. Another very important aspect of this training algorithm is the fact that outlier detection as in ordinary PLS is possible through loadings, scores and residuals. The algorithm is used on a simple non-linear problem concerning fluorescence spectra of white sugar solutions.
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  • 17
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    Journal of Chemometrics 9 (1995), S. 439-439 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 18
    ISSN: 0886-9383
    Keywords: PLS ; kernel algorithm ; multivariate calibration ; EM algorithm ; cross-validation ; missing data ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This is Part II of a series concerning the PLS kernel algorithm for data sets with many variables and few objects. Here the issues of cross-validation and missing data are investigated. Both partial and full crossvalidation are evaluated in terms of predictive residuals and speed and are illustrated on real examples. Two related approaches to the solution of the missing data problem are presented. One is a full EM algorithm and the second a reduced EM algorithm which applies when the number of missing values is small. The two examples are multivariate calibration data sets. The first set consists of UV-visible data measured on mixtures of four metal ions. The second example consists of FT-IR measurements on mixtures consisting of four different organic substances.
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  • 19
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    Journal of Chemometrics 9 (1995), S. 509-520 
    ISSN: 0886-9383
    Keywords: canonical variates ; discriminant analysis ; partial least squares ; principal components ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new set of derived variables is proposed for exhibiting group separation in multivariate data on for preprocessing such data prior to discriminant analysis. The technique combines optimal features of canonical variate analysis and principal component analysis: the derived variables are linear combinations of the original variables that optimize the canonical variate criterion (ratio of between-group to within-group variance) but subject to the orthogonality constraints of principal components. In this formulation the canonical variates can be derived even when the within-group matrix is singular (i.e. when there are more variables than objects in the data matrix). A simple computational algorithm for extraction of these variables is proposed. The methods are illustrated on several data sets and compared with alternative techniques such as principal component analysis and partial least squares.
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  • 20
    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 9 (1995) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 22
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    Journal of Chemometrics 9 (1995), S. 179-195 
    ISSN: 0886-9383
    Keywords: GRAM ; PARAFAC ; rank overlap ; second-order calibration ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: GRAM, a method for second-order calibration, has been introduced by Sanchez and Kowalski and later modified by Wilson, Sanchez and Kowalski. The methods are based on the claim that, in cases without measurement error they yield correct estimates for the concentration ratios and profiles of (rank-one) analytes present in sample and mixture. This claim has not been proven rigorously. In the present paper, rigorous proofs are given for situations where the claims are valid indeed. In addition, it is shown that PARAFAC, an alternative method for second-order calibration, can be used to obtain the same results. Next it is shown that the claims do not hold in cases with ‘rank overlap’ (partly overlapping profiles) and it is proven that a procedure by Wang et al. can still be used to assess some of the concentration ratios. A general framework is provided for a variety of second-order calibration problems and the extent to which quantitative and qualitative information can be expected is given.
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  • 23
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    Journal of Chemometrics 9 (1995), S. 223-225 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 24
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    Journal of Chemometrics 9 (1995), S. 309-322 
    ISSN: 0886-9383
    Keywords: simulated annealing ; messy genetic algorithms ; optimization of multimodal objective functions ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The method of simulated annealing is modified so that the concept of messy chromosomes is applied. Constituent genes of messy chromosomes are specified by their respective names (indices) and values (alleles) simultaneously. Unlike simple chromosomes (binary vectors), messy chromosomes may be either under- or overspecified with respect to the problem being solved. The messy simulated annealing algorithm is a very robust and efficient stochastic optimization method which is able to find correct minima of deceptive or highly multimodal objective functions. This is shown by way of a number of simulations.
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  • 25
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    Journal of Chemometrics 9 (1995), S. ii 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 26
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    Journal of Chemometrics 9 (1995), S. 373-387 
    ISSN: 0886-9383
    Keywords: robust regression ; outliers ; spectroscopy ; calibration ; MASBR (maximum sum of binary coded residuals) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, a novel robust regression method, the maximum sum of binary coded residuals (MASBR), is proposed. Instead of the sum of squared residuals used in least squares regression as the minimization criterion, MASBR regression maximizes the sum of binary coded residuals. MASBR regression is designed for cases where the conventional robust regression methods with breakdown points less than 50% fail. To circumvent the problem of being trapped in local optima, a stepwise-varying acceptable error limit (SVAEL) algorithm is proposed. Both numerical simulation and treatment of real analytical data demonstrate the feasibility of MASBR regression in conjunction with the SVAEL algorithm.
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  • 27
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    Journal of Chemometrics 9 (1995), S. 489-507 
    ISSN: 0886-9383
    Keywords: QSAR ; partial least squares ; robust regression ; CoMFA ; weighted regression ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A robust implementation of partial least squares (PLS) is developed in which the method of iteratively reweighted least squares is adapted for use with PLS. The result is a PLS algorithm which is robust to outliers and is easy to implement. Examples and case studies are presented, followed by two Monte Carlo studies designed to explore the behavior of the method.The paper begins with the motivation and intended applications for the procedure. A discussion is given of the method of interatively reweighted least squares (IRLS) for outlier detection. The procedure, given the name IRPLS, is then presented. Three case studies illustrate how the procedure works on various types of data and how it should be used. The first Monte Carlo study is designed to determine whether the IRPLS procedure correctly identifies multiple outliers in a wide variety of configurations. The second Monte Carlo study is designed to estimate the breakdown bound of the procedure.
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  • 28
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    Journal of Chemometrics 9 (1995), S. 31-58 
    ISSN: 0886-9383
    Keywords: Multivariate curve resolution ; Three-way data analysis ; Factor analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new multivariate curve resolution method is presented and tested with data of various levels of complexity. Rotational and intensity ambiguities and the effect of selectivity on resolution are the focus. Analysis of simulated data provides the general guidelines concerning the conditions for uniqueness of a solution for a given problem. Multivariate curve resolution is extended to the analysis of three-way data matrices. The particular case of three-way data where only one of the orders is common between slices is studied in some detail.
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  • 29
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    Journal of Chemometrics 9 (1995), S. 59-66 
    ISSN: 0886-9383
    Keywords: Mathematical approximation ; Sigmoid curve ; Sensitometric curve ; Photographic material ; Non-linear regression ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper studies the application possibilities of various mathematical analytical functions to models of approximation of sigmoid sensitometric curves of photographic materials. The newly developed functions have been tested along with approximation functions taken from the literature: the former fulfil the statistical criteria of fitting the regression and experimental curve in the best way. The model functions can be used not only for objective determination of sensitometric quantities but also for determination of the general sensitivity (speed) of photographic materials.
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  • 30
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 31
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    Journal of Chemometrics 9 (1995), S. 69-89 
    ISSN: 0886-9383
    Keywords: chemometrics ; pattern recognition ; class modeling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Different estimators of the Mahalanobis distance (such as that based on the Defrise - Gussenhoven correction) are studied and compared with respect to the bias on the distance and the characteristics (sensitivity and specificity) of the class model.Results obtained using estimators with critical values from χ2-statistics are compared with those obtained using estimators with critical values from β-statistics (training set) and Hotelling statistics (evaluation set).Tables are reported for D-statistics (useful for simulating populations of two categories with selectable theoretical sensitivity and specificity) and for critical values of the Mahalanobis distance obtained from β-statistics.For objects of the training set the estimator of the Mahalanobis distance based on the estimate of the covariance matrix produces models with the optimum sensitivity. The same model has too low a sensitivity for objects of the model category in the evaluation set, but good specificity for objects of outer categories.The estimator with the Defrise-Gussenhoven correction produces enlarged models with too high a sensitivity for objects in the training set, good sensitivity for objects of the model category in the evaluation set and low specificity for objects of outer categories.
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  • 32
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    Journal of Chemometrics 9 (1995), S. 139-141 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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  • 33
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    Journal of Chemometrics 9 (1995), S. 169-178 
    ISSN: 0886-9383
    Keywords: minimum volume ellipsoid (MVE) estimators ; robust distance method ; pattern recognition ; Hotelling's T2 statistics ; near-infrared spectra ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method for pattern recognition analysis of near-infrared spectra has been developed using robust distances determined by minimum volume ellipsoid (MVE) estimators of multivariate location and scatter. Classical methods such as the Mahalanobis distance method often fail in the presence of a moderate number of outliers in a training data set, while robust distance methods can tolerate a considerably larger proportion of outliers in a training data set Outliers can be detected by their relatively large robust distances and can be excluded from a training set without a priori knowledge of the nature of the data set. In this paper the properties of a robust distance method are examined using near-infrared spectra of sulfamethoxazole and mixtures with its major degradation products, sulfanilic acid and sulfanilamide. The robust distance method successfully detected unacceptable samples (71.4%-89.3% (α = 0.05) or 78.6%-92.9% (α = 0.10)) even when they were inadvertently included in the training data set.
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    Journal of Chemometrics 9 (1995), S. 226-228 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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  • 35
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    Journal of Chemometrics 9 (1995), S. 229-229 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 9 (1995), S. 283-308 
    ISSN: 0886-9383
    Keywords: simulated annealing ; threshold acceptance ; wavelength selection ; selectivity ; optimization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Simulated annealing (SA) is a stochastic search method that has been applied to combinatorial search problems in chemometrics. Unlike strict iterative improvement methods, SA tolerates temporary moves to detrimental parameter configurations during an optimization. The method used by SA to decide whether or not to accept detrimental steps is a special case of a more general acceptance rule. The present work investigates the performance of various SA-type algorithms that differ only in the acceptance rule for detrimental steps when optimizing continuous or discrete problems. A method for step width modulation is introduced to overcome the poor ability of SA type algorithms to locate the exact extreme of a function. The studied search strategies are modified for the discrete problem of wavelength selection. In order to evaluate SA-type algorithms and their abilities to deal with the wavelength selection problem, two global measures of selectivity are used as criteria to determine the most suitable wavelength subset that maximizes selectivity for pure component ultraviolet-visible spectra.
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    Journal of Chemometrics 9 (1995), S. 329-330 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 38
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    Journal of Chemometrics 9 (1995), S. 331-342 
    ISSN: 0886-9383
    Keywords: partial least squares (PLS) ; variable selection ; IVS-PLS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With the aim of developing PLS models with improved predictive properties, an interactive variable selection (IVS) approach for PLS regression was introduced in Part I of this series. IVS-PLS is based on a dimension-wise selective removal of single elements in the PLS weight vector w. IVS uses cross-validation (CV) as a guiding tool. The present paper illustrates the use of IVS-PLS on both simulated data and real examples from chemistry. In the first example, spectrophotometric data were simulated according to an experimental design. The objective was to see how IVS-PLS was influenced by different levels of noise in X and Y and by the number of predictor variables (K). The results of the modelling are shown as response surfaces. In addition, four real examples were modelled by the IVS-PLS technique. The real data sets were chosen to reflect different types of data from chemistry. For each example a comparison of ‘prediction error sum of squares’ (PRESS) between IVS-PLS and classical PLS is madeFor most of the examples containing many predictor variables IVS-PLS shows an improvement in predictive properties over classical PLS. Also, improvements for IVS-PLS2 (modelling of more than one y-variable) models were found. For data sets with a moderate number of variables the influence of the IVS method becomes less pronounced.
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    Journal of Chemometrics 9 (1995), S. 389-409 
    ISSN: 0886-9383
    Keywords: multivariate image analysis ; principal component analysis ; exploratory data analysis ; projection in multivariate space ; graphical visualization ; noise ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multivariate image analysis (MIA) is a powerful tool for many image segmentation and classification problems, but the interpretation and understanding of the original and resulting multidimensional (multivariate) data are not always easy. A strategy for MIA has been proposed which describes its usage on multivariate images for segmentation tasks. MIA starts with principal component analysis (PCA) and then continues with interactive analysis of the output from PCA. In this paper a number of extensions to MIA are proposed. The extensions are the suggestion to incorporate preprocessing of the multivariate image in MIA, the suggestion to use synthetic multivariate image models which create a clear-cut situation, and new visualization tools which improve the interactivity and understanding of the results. Extended MIA is applied on synthetic multivariate image data simulating a possible application with large noise, positron emission tomography (PET). As a result of the interactive analysis, suggestions for preprocessing emerge. The developed methodology for handling the noise is then applied on real PET image data with good results.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 41
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    Keywords: sequential response surface modelling ; Williamson ether synthesis ; SN2 ; optimization ; reaction kinetics ; reaction mechanism ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work the utility of a new method for determining kinetic parameters by sequential response surface modelling, previously described (Part 1), is shown by applying it to an experimental study of a reaction with known kinetics. The nucleophilic substitution reaction between ethoxide and benzyl chloride, the Williamson ether synthesis, was selected as a model reaction. This reaction is known to proceed with second-order kinetics. The method gives access to estimates of initial reaction rate which can be further used to obtain estimates of activation energy and reaction order of reactants. The results obtained are in good agreement with the estimated values of these parameters obtained with conventional kinetic experiments.
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    Journal of Chemometrics 9 (1995), S. 483-487 
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    Keywords: fractional factorial design ; multiresponse ; PLS ; PCA ; reduced-rank regression ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper presents an interpretation of PLS applied to orthogonal explanatory variables. In particular, it is shown that in fractional factorial multiresponse experiments PLS2 gives identical results to ordinary least squares applied to principal components of the response variables. The general relationship is that the reduced-rank regression algorithm which first projects Y onto the X-space and then truncates this matrix by principal component analysis before performing ordinary least squares estimation gives the same predictor as PLS2 and SIMPLS if all the non-zero eigenvalues of XTX are identical.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 9 (1995) 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 9 (1995), S. 1-2 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 9 (1995), S. 3-20 
    ISSN: 0886-9383
    Keywords: Deconvolution algorithms ; Instrumental analysis ; Spectrometry ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deconvolution algorithms for measurand reconstruction are considered. Their metrological and numerical properties are briefly characterized. Six algorithms most frequently used for instrumental applications are selected for closer analysis. Their comparative study is based on the use of spectrometric-type synthetic data, calorimetric-type synthetic data and spectrometric real-world data. Conclusions concerning computational complexity and accuracy of the compared algorithms as well as their metrological applicability are drawn.
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    Journal of Chemometrics 9 (1995), S. 67-68 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 9 (1995), S. 125-135 
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    Keywords: Procrustean analysis ; FT-IR spectroscopy ; NIR spectroscopy ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Procrustean methods allow the fitting of a given matrix to another given matrix observed on the same objects. In the traditional approach orthogonal constraints are imposed upon the transformation matrix, whereas in the alternative approach Procrustean analysis may be performed without such constraints. The two methods (with and without constraints) were compared on data dealing with mid- and near-infrared spectra of oil. The aim was to reconstruct the mid-infrared spectral information using data from the near-infrared spectra. Unconstrained Procrustean analysis proved to be the more efficient for both the calibration and verification sets. Furthermore, the analysis of the transformation matrix between the two infrared ranges made it possible to indicate wavelengths and wave numbers corresponding to the same chemical groups.
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    Journal of Chemometrics 9 (1995), S. 91-123 
    ISSN: 0886-9383
    Keywords: H-principle ; PCA ; PLS regression ; latent variable models ; quadratic models ; sensitivity analysis ; outlier tests ; prediction variances ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present here an algorithmic approach to modelling data that includes principal component analysis (PCA) and partial least squares (PLS). In fact, the numerical algorithm presented can carry out PCA or PLS. The algorithm for linear analysis and extensions to non-linear analysis applies to both PCA and PLS. The algorithm allows for combination of PCA and PLS types of models and therefore extends modelling to new types of models that involve combination of regression models and ‘selection of variation’ models, which is the idea of PCA-type models. The fact that the algorithm carries out both PCA and PLS shows that PCA and PLS are based on the same theory. This theory is based on the H-principle of mathematical modelling. The algorithm allows tests for outliers, sensitivity analysis and tests of submodels. These aspects of the algorithm are treated in detail. We compute various measures of sizes, e.g. of components, of the covariance matrix, of its inverse, etc. that show how much the algorithm has selected at each step. The analysis is illustrated by data from practice.
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    Journal of Chemometrics 9 (1995), S. 232-236 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 54
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    Keywords: multiway data ; standard addition method ; calibration ; matrix effects ; trilinear decomposition ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: Presented here is an algorithm for analysis of second order data by the method of standard additions. The method of standard additions is applicable when matrix effects make traditional calibration unreliable. The algorithm employs a generalized eigenproblem to mathematically separate the instrument response of the analyte from the instrument response of any interfering species. A scheme for determining the eigenvectors (and hence the concentration estimate) that uniquely correspond to the analyte of interest is given. These eigenvectors can readily be distinguished from any eigenvector that corresponds to the spectrum of the interferents or both the interferents and analyte. The stability of the estimated analyte concentration is verified by Monte Carlo simulations. The algorithm is applied to the analysis of trichloroethylene in samples that have matrix effects caused by an interaction with chloroform.
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    Journal of Chemometrics 9 (1995), S. 327-328 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 9 (1995), S. 343-362 
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    Keywords: straight line calibration ; errors in both axes ; uncertainties ; linear regression ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calibration is a fundamental step in the calculation of the unknown concentration of analyte in most analytical methods. It is known that for certain methodologies, if only the errors in the independent variable are taken into account, there may be considerable errors in the estimation of the value of the regression coefficients, the derived statistical parameters and in some cases the sought for response and concentration values. This paper reviews the calibration methods including some references to procedures for the detection of outliers and robust regression when there are errors in both axes. The advantages and limitations of the different approaches are discussed and a comparative study is made of the approaches of several techniques for which computer programmes have been developed based on the algorithms put forward by the different authors. Finally, some trends of future development in this field are envisaged.
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    Journal of Chemometrics 9 (1995), S. 411-422 
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    Keywords: gasoline ; classification ; multiple regression ; non-correlated variables ; accuracy of measurements ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A procedure for the classification of motor gasolines by their trend to carburettor icing has been proposed. For this goal a set of regression models was employed. Motor gasoline classification was carried out in terms of the isopropyl equivalent using seven physicochemical properties.
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    Journal of Chemometrics 9 (1995), S. 431-432 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 9 (1995), S. 531-531 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 3 (1980), S. 89-90 
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    Keywords: Gas chromatography ; Capillary, glass ; Histamine TMS derivatives, complete separation, 2 minutes ; NPD used for quantitation down to 20 pg ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complete separation of the TMS derivatives of histamine, 1-methyl histamine and 3-methyl histamine was achieved in two minutes in a 7 m × 0.25 mm column coated with SP 2250. Using NPD, histamine was detectable at levels as low as 20 pg. This offers a rapid, sensitive procedure with potential for clinical diagnosis and food analysis.
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    Journal of High Resolution Chromatography 3 (1980), S. 301-302 
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    Keywords: Gas chromatography ; Polychlorinated biphenyls ; Liquid crystal phase ; Choice of stationary phases for analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 3 (1980), S. 305-306 
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    Keywords: Liquid chromatography, micro HPLC ; Temperature effect ; Cooled column ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 3 (1980), S. 313-314 
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    Keywords: Liquid chromatography ; Broadening effect ; Connecting tube ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 3 (1980) 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 3 (1980), S. 337-344 
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    Keywords: Gas Chromatography ; Capillary, glass ; Surface deactivation ; High temperature silylation ; Applications ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: This paper describes the results of a study on the deactivation of the surface of glass capillary columns by high temperature silylation (HTS). The different steps, leaching, washing, dehydration and HTS were optimized. A practical procedure yielding a high percentage of very good columns is given. The influence of leaching and HTS on the temperature stability and coating efficiency of capillary columns coated with OV-1 was studied. The inertness of the glass surface after HTS is demonstrated by several examples.
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    Journal of High Resolution Chromatography 3 (1980), S. 351-352 
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    Keywords: Gas chromatography ; Injector ; Concentrator ; Electrically heated inlet ; Capillary columns ; Vapor sampler ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 3 (1980), S. 355-356 
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    Keywords: Gas-liquid chromatography (GLC) ; Open tubular glass capillary columns ; Blended stationary phases ; Liquid crystals ; Polycyclic aromatic hydrocarbons (PAH) ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 3 (1980), S. 362-370 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 3 (1980), S. 371-371 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 3 (1980), S. 381-394 
    ISSN: 0935-6304
    Keywords: Gas-liquid chromatography ; Capillary columns ; Steroids, prostaglandins, drugs ; Metabolites ; Derivatization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article describes the development of the application of capillary column GLC methods to steroids, prostaglandins and especially drugs and their metabolites in samples of biological origin. The wide variety - in terms of structures and pharmacological properties - of drugs now analyzed by capillary column GLC is made evident. Reasons for use of capillary rather than packed columns are given. The frequent use of and need for derivatization procedures prior to chromatography is emphasized. A bibliography of 83 references is included in the manuscript.
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    Journal of High Resolution Chromatography 4 (1981), S. 11-16 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary, glass ; SCOT column ; Coating, liquid phase ; Single-step coating ; Phenols ; Phenolic acids ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A single-step coating method for the preparation of glass capillary SCOT columns is described. It is reproducible and less time-consuming than the well-known two-step coating procedures. Other methods attempted are discussed briefly. Both the flame ionization and electron capture detectors could be used in conjunction with temperature programming. The separations achieved with an “activity mixture”, phenols and phenolic acids, illustrate the resolution obtained. The columns are suitable for quantitative determinations and a comparison is made with a conventional packed column.
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    Journal of High Resolution Chromatography 4 (1981), S. 38-39 
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    Keywords: Gas chromatography ; Fused silica capillary column ; Activity ; Hydroxylated surfaces ; Dehydroxylated surfaces ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 4 (1981), S. 83-85 
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    Keywords: HPLC ; Nanoliter volume detector ; 1.5 × 10-5 AU noise (0.1 μl 0.1% benzene in methanol) ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 4 (1981), S. 95-96 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 4 (1981), S. 115-120 
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    Keywords: TLC ; Gradient and continuous development ; Amino acids ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thin-layer gradient elution chromatography is a convenient technique for separation of very complicated mixtures; in some cases the gradient technique can be replaced by continuous development. The two techniques are compared in practice by using them to separate a mixture of dabsyl derivatives of amino acids.
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    Journal of High Resolution Chromatography 4 (1981), S. 123-124 
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    Keywords: (GC)2 in short capillaries ; Liquid crystalline stationary phase ; Supercooled temperature range ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 4 (1981), S. 132-134 
    ISSN: 0935-6304
    Keywords: Liquid chromatography, HPLC ; Ion-pair reversed-phase HPLC ; Chlorhexidine in pharmaceutical preparations ; Quantitation within 0.66-3.41% relative standard deviation ; 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 4 (1981), S. 142-142 
    ISSN: 0935-6304
    Keywords: 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 4 (1981) 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 82
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    Journal of High Resolution Chromatography 4 (1981) 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 83
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    Journal of High Resolution Chromatography 3 (1980), S. 33-34 
    ISSN: 0935-6304
    Keywords: HPLC bonded phases ; Picramidopropyl silica ; Charge transfer HPLC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 84
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    Journal of High Resolution Chromatography 3 (1980), S. 62-68 
    ISSN: 0935-6304
    Keywords: Gas Chromatography ; Adsorption on glass surface, no peak shade deformation ; Radioactivity, test to show systematic loss by sorption ; Phenytoin ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The labelled drug [14C] phenytoin was injected into an all-glass chromatographic system to determine adsorption on various system parts. It appeared that 10 to 20% of the amount injected did not elute. Severity of adsorption as measured from lasting radioactivity was not anticipated from peak shape or calibration curves.
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  • 85
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    Journal of High Resolution Chromatography 3 (1980), S. 86-86 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Recycle chromatography ; Multiple-pass chromatography ; Thermal focussing ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 86
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    Journal of High Resolution Chromatography 3 (1980), S. 146-146 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Cold trap heating ; Thermal focussing ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 87
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    Journal of High Resolution Chromatography 3 (1980), S. 152-152 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 88
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    Journal of High Resolution Chromatography 3 (1980), S. 11-15 
    ISSN: 0935-6304
    Keywords: GC instrument conversion ; All-glass GC-2 system ; Phenols ; Hydrocarbons ; Terpenoids ; Linear response ; Reproducibility ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two regular GC instruments were modified with injection port liners, split-mode injection systems, pressure regulators, effluent traps and needle valves to produce an all-glass GC-2 system. This simple and inexpensive system allows the quantitative analyses of phenols, hydrocarbons, acids, sterols, terpenoids, and alkaloids with excellent reproducibility and linear response. Even more impressive was its ability to analyze a C45-terpenoid alcohol, solanesol, as its TMS-derivative (M.W. 702).
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  • 89
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    Journal of High Resolution Chromatography 3 (1980), S. 28-28 
    ISSN: 0935-6304
    Keywords: Chemical reaction chromatographic analysis ; Two six-port valves for reaction analysis ; Two six-port valves connection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 90
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    Journal of High Resolution Chromatography 3 (1980), S. 25-27 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Instrumental modification to multidimensional separation ; Application with packed columns on complex sample composition ; Indene to pyrene range in coal tar ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 91
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    Journal of High Resolution Chromatography 3 (1980), S. 199-204 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 92
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    Journal of High Resolution Chromatography 3 (1980), S. 206-207 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 93
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    Journal of High Resolution Chromatography 3 (1980), S. 79-84 
    ISSN: 0935-6304
    Keywords: Thin-layer chromatography, TLC ; Mobile phase parameters and RM-value ; Influence of surface of adsorbed molecules ; Non-active binary mobile phases ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The purpose of the studies being carried out is to find some regularities of a general character which determine the relationship between the structures of the chromatographed substances and the composition of the mobile phase, i.e., between the log of the partition coefficient of the sample (Az), the K1-values which characterize the adsorption equilibrium of component “1” in a given chromatographic system, the structures of the mobile phase components and the structures of the substances being chromatographed. This paper deals with the relationship between the Az and K1 parameters and the structure of naphthalene and a number of its derivatives. It has been shown that there is a close relationship between the kind, size, frequency and site of the substituent on the one hand and the Az and K1 values on the other. In order to eliminate the possibility of unwanted side effects, the investigations were carried exclusively using non-active binary mobile phases of the type N + N or N + /B/. From these investigations, a comparison between the parameter Az and the surface of adsorbed molecules (As) was also possible.
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  • 94
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    Journal of High Resolution Chromatography 3 (1980), S. 91-91 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary, glass ; Static coating technique details ; End-sealing without failure, under ethanol ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 95
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    Journal of High Resolution Chromatography 3 (1980), S. 95-100 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 96
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    Journal of High Resolution Chromatography 3 (1980), S. 101-101 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 97
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    Journal of High Resolution Chromatography 3 (1980), S. 133-142 
    ISSN: 0935-6304
    Keywords: HPLC, UV and EC ; Detector response ratios ; Impurities in Phenol ; Identification using HPLC ; Hydroquinone ; Catechol ; Inactivation of RNA ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several impurities which were suspected to be present in commercial reagent-grade phenol were separated using high performance liquid chromatography following sample concentration by steam distillation. A reverse-phase, microparticulate column and 5 solvent systems containing 5% to 25% methanol in 0.05 M phosphoric acid were used. A variable wavelength ultraviolet detector and an electrochemical detector were connected in series, in that order, to the column. Capacity factors (ḱ) for pyrogallol, hydroquinone, resorcinol, catechol, orcinol and phenol were determined in the 5 solvent systems and compared to ḱ-values of impurities present in the residue remaining from the steam distillation of phenol. Co-chromatography of standards suspected as contaminants and possessing ḱ-values similar to those of impurities were carried out in 3 solvent systems to confirm identical retention characteristics. Detector response ratios of contaminants and suspected standards, using various wavelengths and voltage potential settings, were utilized as major identification parameters. Two of the several contaminants separated were identified as hydroquinone and catechol.
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  • 98
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    Journal of High Resolution Chromatography 3 (1980), S. 149-150 
    ISSN: 0935-6304
    Keywords: HPTLC ; Rel. quantitative alkaloid determination ; 5% standard deviation in adsorption mode ; 3% standard deviation in fluorescence mode ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A direct densitometric method for the quantitative measurement of reserpine and ajmaline in whole roots and bark of roots of Rauwolfia Vomitoria, after extraction and separation by thin-layer chromatography, is described. The emission and excitation spectra of the reserpine and the absorption spectrum of the ajmaline were scanned. The linear range between peak area and concentration is given.
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  • 99
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    Journal of High Resolution Chromatography 3 (1980), S. 189-190 
    ISSN: 0935-6304
    Keywords: Thin-layer chromatography ; Circular mode ; Partially alkylated reversed-phases plates ; Water concentration in mobile phase of great influence ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 100
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    Journal of High Resolution Chromatography 3 (1980), S. 195-195 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Columns, packed ; High resolution ; Packing apparatus ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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