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  • Analytical Chemistry and Spectroscopy  (1,441)
  • Humans  (503)
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  • 1990-1994  (1,944)
  • 1992  (1,944)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 35 (1992), S. 7-16 
    ISSN: 1432-1432
    Keywords: Alu source genes ; Humans ; Gorillas ; Retrotransposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A member of the young PV Alu sub-family is detected in chimpanzee DNA showing that the PV subfamily is not specific to human DNA. This particular Alu is absent from the orthologous loci in both human and gorilla DNAs, indicating that PV subfamily members transposed within the chimpanzee lineage following the divergence of chimpanzee from both gorilla and human. These findings and previous reports describing the transpositional activity of other Alu sequences within the human, gorilla, and chimpanzee lineages provide phylogenetic evidence for the existence of multiple Alu source genes. Sequences surrounding this particular Alu resemble known transcriptional control elements associated with RNA polymerase III, suggesting a mechanism by which cis-acting elements might be acquired upon retrotransposition.
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  • 2
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    Springer
    Journal of molecular evolution 34 (1992), S. 336-344 
    ISSN: 1432-1432
    Keywords: Humans ; Mitochondrial DNA ; Nuclear polymorphisms ; Heteroplasmy ; Genetic differentiation ; Sickle cell ; Rain forest refuges
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The identification of genetically coherent populations is essential for understanding human evolution. Among the culturally uniform ethnic groups of west Africa, there are two geographically distinct populations with high frequencies of sickle-cell hemoglobin (HbS). Although the HbS mutation in each group is found on distinguishable chromosomes 11, these populations have been assumed to be parts of a single population. Analysis of mitochondrial DNA (mtDNA) in these populations demonstrated that the two populations identified by alternative chromosomes 11 bearing HbS have distinct distributions of mitochondrial genotypes, i.e., they are maternally separate. These studies also showed that, contrary to expectation, the mtDNA of some individuals is heteroplasmic. For nuclear loci, a comparison of the frequency of alternative alleles established that these populations are genetically distinct. Both the mitochondrial and nuclear data indicate that these populations have been separate for approximately 50,000 years. Although HbS in the two populations is usually attributed to recent, independent mutations, the duration of the separation and the observed geographic distribution of the population allow for the possibility of an ancient origin of HbS. Assuming an ancient mutation and considering the known biogeography, we suggest that HbS protected selected populations from malaria in rain forest refuges during the most recent ice age.
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  • 3
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 6 (1992) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 4
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 6 (1992), 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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  • 5
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 6 (1992), S. 63-64 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 6
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 6 (1992), S. 65-83 
    ISSN: 0886-9383
    Keywords: Trilinear decomposition ; Receptor modeling ; Source identification ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In many cases, monitoring data for ambient airborne particles can be organized in the form of a three-way data table with one way for chemical species, one for sampling periods and one for sites. A direct trilinear decomposition followed by a matrix reconstruction (DTDMR) is developed to analyze such a data table as a whole. The three-way data set is composed into three two-way matrices by a direct trilinear decomposition (DTD). The column vectors of each of the matrices are called ‘source profiles’, ‘emission patterns’ and ‘site coefficients’ respectively. Particulate sources are identified by examining both their source profiles and emission patterns. After the sources have been identified, emission patterns and site coefficients are used to produce a three-way matrix that gives estimates of mass contributions of sources to the samples collected at every site in every period. By simulation study, not only has the method been verified, but a good indicator has been found that shows the number of factors (i.e. sources) in the system. Unlike other receptor models, DTDMR does not require source profile data and does not involve trial-and-error procedures. Since DTDMR identifies sources based on variations in two dimensions, it has a higher potential to distinguish two sources that have similar chemical compositions. The DTDMR model has provided excellent results with simulated data and has been applied in a real world three-way data set.
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  • 7
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 6 (1992), S. 113-116 
    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 6 (1992), S. 117-118 
    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
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 6 (1992), S. 151-161 
    ISSN: 0886-9383
    Keywords: NIR spectroscopy ; Wavelength selection ; Interaction effects ; Multicomponent mixtures ; Partial least squares ; Generalized least squares ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Modern scanning (near-)infrared reflectance/absorption (NIR) spectroscopes measure the absorptions or reflectances at a sequence of around 1000 wavelengths. Training data may consist of 10-100 carefully designed sample mixtures for which the true composition of the mixture is either known by formulation or accurately determined by wet chemistry. In future one wishes to predict the true composition from the spectrum. In this paper we compare a simple wavelength selection approach with methods which retain all the wavelengths. It offers a powerful yet simple technique for choosing those wavelengths that are specific to each pure component as against the other components (including the medium) for the varying compositions. In the presence of a defined range of ingredients in thus chooses wavelengths which are highly selective for each particular component. It has the added advantage of selecting wavelengths which are little effected by interaction effects and consequent non-linearities.The calibration data used consist of 125 observations of three sugars, each varying at five levels in a full 53 design. The validation set consists of 21 further samples specially selected to have compositions outside the range of the training sample. The selection methods perform much better on this prediction set than methods which retain all the wavelengths, 700 in this case. The leave-one-out cross-validation internal to the calibration data would point to the opposite finding and suggests that such crossvalidations may be overly flattering to techniques such as partial least squares and may encourage overfitting. After selection, simple straightforward least squares methods may be used, eschewing the need for ‘shrinkage’ methods such as partial least squares or ridge regression.
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  • 10
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    Journal of Chemometrics 6 (1992), S. 247-255 
    ISSN: 0886-9383
    Keywords: Analysis of variance ; Assumptions ; Graphics ; Models ; Validation of model ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The computer has made it possible to scrutinize data rapidly by means of graphics. This should be done prior to the application of any model to the data, since the model must be validated before using it as a means of analyzing the data. The procedure is illustrated in terms of two examples of real experimental data.
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  • 11
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    Journal of Chemometrics 6 (1992), S. 284-285 
    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 6 (1992), S. 307-334 
    ISSN: 0886-9383
    Keywords: Non-linear PLS ; Quadratic regression ; Non-linear models ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We treat here an extension of linear PLS regression to include regression on quadratic PLS components. The quadratic regression can be viewed as a natural extention of linear PLS regression to quadratic PLS according to the H-principle of mathematical modelling. The numerical implementation is treated in detail. It is shown that this approach can be used for models with large numbers of variables. Some modelling strategies are discussed depending on the purpose of the modelling. Applications of this approach are treated.
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  • 13
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    Journal of Chemometrics 6 (1992), S. 357-357 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 14
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 6 (1992) 
    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 6 (1992), S. 29-40 
    ISSN: 0886-9383
    Keywords: Factor analysis ; Window factor analysis ; Multicomponent analysis ; Flow injection analysis ; Self-modeling curve resolution ; Bismuth chloride complexes ; 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 method for extracting the concentration profiles of individual components from evolutionary processes such as flow injection, chromatography, titrations and reaction kinetics. The method takes advantage of the fact that each component lies in a specific region along the evolutionary axis, called the window. Theoretical equations are derived. The method is used to extract the concentration profiles and spectra of seven bismuth species from data obtained by Gemperline and Hamilton, who injected bismuth perchlorate into a flowing stream of hydrochloric acid.
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  • 16
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    Journal of Chemometrics 6 (1992), S. 57-62 
    ISSN: 0886-9383
    Keywords: Closure ; Baseline ; Mean centering ; Rank ; Exploratory data analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper describes an investigation into the relationship of closure, a baseline offset and mean centering to the interpretation of matrix rank. The equivalence of a certain type of closure to a constant baseline (i.e. a simple numerical offset which may vary between response channels but is constant over all samples) is demonstrated. A systematic approach to the interpretation of the rank of a matrix is given.
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  • 17
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    Journal of Chemometrics 6 (1992), S. 97-102 
    ISSN: 0886-9383
    Keywords: Between-group variances ; Canonical variate criterion ; Eigenvalues ; Eigenvectors ; Orthogonal projection ; Within-group variance ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Canonical variate analysis is the appropriate descriptive technique for multivariate data which have an a priori group structure, but problems arise with this technique when there are more variables than within-group degrees of freedom because of singularity of matrices. In such cases it is shown through illustrative examples that principal component analysis is a viable substitute provided that the principal components are ranked according to the canonical variate criterion (ratio- of between- to within-group variances) rather than the usual criterion of total variance. This ranking can also be used to select components for subsequent discriminant analysis.
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  • 18
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    Journal of Chemometrics 6 (1992) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 19
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    Journal of Chemometrics 6 (1992), S. 119-133 
    ISSN: 0886-9383
    Keywords: Mass spectra ; Classification ; Structure description ; Fragmentation ; Ion series ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to investigate correlations between the functionality of compounds and the classification of their mass spectra, low-resolution spectra of monofunctional compounds have been classified by four supervised classification methods. The new classes are characterized by structural features and the correlation between functionality and classification is explained by fragmentation rules. Systematic misclassifications show that low-resolution mass spectra alone are not suitable for reliable identification of functionality.
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  • 20
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    Journal of Chemometrics 6 (1992), S. 163-175 
    ISSN: 0886-9383
    Keywords: Multiple-correspondence analysis ; Starch granule description ; Image analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Raw starch is composed botanically of characteristic granules of various sizes and shapes, so that each kind of starch may be characterized by the population of its granules. In the present study ten commercial starch species were studied: wheat, rice, manioc, potato, arrowroot, amylomaize, normal maize, waxy maize and two different banana species. Six variables measuring the size and shape of granules were obtained by image analysis. The objective was to find a method to describe and compare the granule populations of the ten species. For such a study, multiple-correspondence analysis (MCA) was applied. MCA makes it possible to draw similarity maps of categories and objects. For each starch species the frequency distributions (histograms) of the six variables were assessed and each granule was characterized by its species and the classes of histograms to which it belonged. MCA was applied to the granule table and a description of the histogram classes and the granules was obtained. From the variables description a general typology of the granules was deduced. The similarity maps showed considerable scatter of the granules for all species except rice. A particular species could therefore not be identified by a single granule, but the granule distribution seemed to be characteristic. MCA was an appropriate method to analyse these data because it points out non-linear relationships between quantitative and qualitative variables.
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  • 21
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    Journal of Chemometrics 6 (1992), S. 177-188 
    ISSN: 0886-9383
    Keywords: PLS ; Prediction error ; Background constituents ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A modification of a technique proposed by Lorber and Kowalski for the estimation of prediction errors is presented. The method is applied to five data sets. The results show that for some data sets the estimated prediction errors are close to the actual prediction errors for samples within the calibration range, while samples outside the calibration range must be background corrected before quantification of the prediction error.
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  • 22
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    Journal of Chemometrics 6 (1992), S. 189-198 
    ISSN: 0886-9383
    Keywords: Robust regression ; Partial least squares ; QSAR ; Perturbation study ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A robust partial least squares (PLS) regression algorithm is developed. This is achieved by substitution of the univariate regression steps in the iterative PLS2 algorithm by a robust alternative. The angle between loading vectors from both perturbed and unperturbed solutions is used as a measure of robustness. By means of a perturbation study on a structure-activity data set, it is demonstrated that the stability of the robust method is superior to standard PLS.
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  • 23
    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 6 (1992) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 25
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    Journal of Chemometrics 6 (1992), S. 267-281 
    ISSN: 0886-9383
    Keywords: Genetic algorithms ; Feature selection ; Multivariate analysis ; Optimization methods ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Genetic algorithms have been created as an optimization strategy to be used especially when complex response surfaces do not allow the use of better-known methods (simplex, experimental design techniques, etc.). This paper shows that these algorithms, conveniently modified, can also be a valuable tool in solving the feature selection problem. The subsets of variables selected by genetic algorithms are generally more efficient than those obtained by classical methods of feature selection, since they can produce a better result by using a lower number of features.
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  • 26
    ISSN: 0886-9383
    Keywords: Derivatization reaction ; Factorial design ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A number of nucleophiles have been successfully identified and quantified using the Kröhnke reaction with 2,3-diphenyl derivatives of quinolizinium salts. Optimization of the reaction conditions by means of a mathematical model involving analysis of the response surface has led to a better understanding of the factors exerting an influence on the above reaction.The parameters chosen were temperature, reaction time, base concentration, water concentration and nucleophile concentration. The reaction was developed in polar aprotic solvents (acetone, acetonitrile). To facilitate the nucleophilic attack, the presence of an organic base (triethylamine) was necessary, although concentrations in excess of 0·15M did not alter the development of the reaction. Since pharmaceutical solutions are often aqueous, the influence of water on the reaction was studied. Low water volumes have no significant influence on the opening of the quinolizinium ring by the nucleophilic reagent. However, when the water proportion exceeded that of the organic solvent, the fluorescence intensity was lower than expected. Development of the fluorescent reaction product was first detected 5 min after the reaction started. The fluorescence intensity reached its optimum value after 138 min.
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  • 27
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    Journal of Chemometrics 6 (1992), 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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  • 28
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    Journal of Chemometrics 6 (1992), S. 85-96 
    ISSN: 0886-9383
    Keywords: Optimization ; Calibration ; Simulated annealing ; Experimental design ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper utilizes variable step size generalized simulated annealing (VSGSA) to design multicomponent calibration samples for spectroscopic data. VSGSA is an optimization procedure which is capable of converging to exact positions of global optima located on multidimensional continuous functions. On the basis of analysis sample response vectors, optimally designed calibration concentration matrices are obtained assuming knowledge of components present. The complexity of response surfaces established by the optimization criteria is described.
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  • 29
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    Journal of Chemometrics 6 (1992), S. 103-111 
    ISSN: 0886-9383
    Keywords: Mean centering ; Preprocessing ; Multivariate calibration ; Error propagation ; Principal component regression (PCR) ; Partial least squares (PLS) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Traditionally, one form of preprocessing in multivariate calibration methods such as principal component regression and partial least squares is mean centering the independent variables (responses) and the dependent variables (concentrations). However, upon examination of the statistical issue of error propagation in multivariate calibration, it was found that mean centering is not advised for some data structures. In this paper it is shown that for response data which (i) vary linearly with concentration, (ii) have no baseline (when there is a component with a non-zero response that does not change in concentration) and (iii) have no closure in the concentrations (for each sample the concentrations of all components add to a constant, e.g. 100%) it is better not to mean center the calibration data. That is, the prediction errors as evaluated by a root mean square error statistic will be smaller for a model made with the raw data than a model made with mean-centered data. With simulated data relative improvements ranging from 1% to 13% were observed depending on the amount of error in the calibration concentrations and responses.
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  • 30
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    Journal of Chemometrics 6 (1992), S. i 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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  • 31
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    Journal of Chemometrics 6 (1992), S. 135-150 
    ISSN: 0886-9383
    Keywords: 2D surface ; Multivariate analysis ; Non-congruent ; Unfolding ; Folding ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of latent variable projection for analysis of non-congruent 2D surfaces is presented. We give a formal description of the folding/unfolding process. A simulated 2D oscillator evolving in time is studied in detail to illustrate interpretation aspects of the method.
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    Journal of Chemometrics 6 (1992), S. i 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 33
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    Journal of Chemometrics 6 (1992), S. 199-216 
    ISSN: 0886-9383
    Keywords: MARS ; Splines ; Multivariate calibration ; Non-linear ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This tutorial paper presents a simplified view of one of the more recently published multivariate calibration methods particularly suited to dealing with non-linear data sets. The method is referred to as MARS and stands for multivariate adaptive regression splines. Simple examples are provided to explain the workings of the method.
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    Journal of Chemometrics 6 (1992), S. 228-228 
    ISSN: 0886-9383
    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 6 (1992), S. 229-229 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 36
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    Journal of Chemometrics 6 (1992), S. 231-246 
    ISSN: 0886-9383
    Keywords: Integration methods ; Taylor series method ; Optimization methods ; Kinetic mechanisms ; Kinetic determinations ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general equation to derive kinetic models up to any order is given. This equation greatly facilitates the application of the Taylor series method to the integration of kinetic models up to very high orders. When dealing with non-stiff models, computing time is always reduced by increasing the integration order, at least up to the 20th order. When the model is stiff, the integration order should be optimized; however, a twelfth order is recommended to integrate weakly stiff models. The use of an algorithm which permits the immediate calculation of the integration step size required to maintain a given accuracy leads to further reductions in computing time. When implemented as recommended here, a high-order Taylor series method is more rapid and accurate than Runge-Kutta and predictor-corrector methods and can be advantageously used in combination with optimization methods to perform mechanism studies and in multicomponent kinetic determinations.
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  • 37
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 38
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    Journal of Chemometrics 6 (1992), S. 289-305 
    ISSN: 0886-9383
    Keywords: Chemical structure database ; Conformational searching ; Similarity searching ; Substructure searching ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper presents a review of the rapid developments that have taken place over the last few years for the searching of databases of three-dimensional (3D) molecules. The geometric arrangement of the atoms in a 3D molecule is described by an interatomic distance matrix. This is a form of labelled graph that can thus be searched using the subgraph-isomorphism algorithms that are widely used for searching databases of two-dimensional (2D) molecules. Several in-house and commercial systems have been developed for 3D database searching that are based on such techniques. These systems are reviewed and their effectiveness demonstrated by examples of their use in the discovery of novel, biologically active molecules. Current systems represent a molecule by one or a small number of low-energy conformations and there is hence much interest in the development of representational techniques and searching algorithms that account for the full set of geometric arrangements that can be adopted by a flexible molecule.
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  • 39
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    Journal of Chemometrics 6 (1992) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 40
    ISSN: 0886-9383
    Keywords: GOLPE ; PLS ; Regression ; SDEP ; Variable selection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A procedure called GOLPE is suggested in order to detect those variables which increase the predictivity of PLS models. The procedure is based on evaluating the predictive power of a number of PLS models built by different combinations of variables selected according to a factorial design strategy. Examples are given of the efficiency of this variable selection procedure, which shows how these predictive PLS models are better than those obtained by all variables and better than the corresponding ordinary regression models.
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  • 41
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    Journal of Chemometrics 6 (1992), S. 11-28 
    ISSN: 0886-9383
    Keywords: Three-way PLS ; PARAFAC ; Unfolding ; Validatory tools ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The methods PARAFAC and three-way PLS are compared with respect to their ability to predict reversed-phase retention values. Special attention is paid to simple validatory tools, the meaning and use of which are explained.
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  • 42
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    Journal of Chemometrics 6 (1992), S. 41-56 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The principal properties, here called the ρ-scales, of peat have been calculated on the basis of chemical analysis. The scales were derived from quantitative contents of carbohydrates, Klason lignin, amino acids, amino sugars and conventional chemical peat measurements. The variation in the chemical parameters was compressed using principal component analysis (PCA). Partial least squares (PLS) regression was used for prediction of botanical, microbial, physical and dewatering data. A rapid estimation of the scales has been made from near-infrared (NIR) spectroscopy and offers, indirectly, rapidly obtainable, chemically interpretable, biological information. A reduced scale based on carbohydrate data was also tested. The ρ-scales offer an interface between different areas of peat research. Strategies are outlined for the selection of a subset of chemical measurements among the variables used for characterization. A multivariate strategy based on these ideas is discussed.
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  • 43
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    Journal of Chemometrics 6 (1992) 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 44
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    Journal of Chemometrics 6 (1992), S. 217-225 
    ISSN: 0886-9383
    Keywords: Principal component regression ; Calibration ; Optimality ; Principal component selection ; Quantitative structure-activity relationship ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Principal components (PCs) for principal component regression (PCR) have historically been selected from the top down for a reliable predictive model. That is, the PCs are arranged in a list starting with the most informative (PC associated with the largest singular value) and proceeding to the least informative (PC associated with the smallest singular value). PCs are then chosen starting at the top of this list. This paper discusses an alternative procedure of treating PC selection as an optimization problem. Specifically, without any regard to the ordering, the optimal subset of PCs for an acceptable predictive model is desired. Five data sets are analyzed using the conventional and alternative approaches. Two data sets are spectroscopic in nature, two data sets deal with quantitative structure-activity relationships (QSARs) and one data set is concerned with modeling. All five data sets confirm that selection of a subset without consideration to order secures the best results with PCR. One data set is also compared using partial least squares 1.
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    Journal of Chemometrics 6 (1992), S. i 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 46
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    Journal of Chemometrics 6 (1992), S. 257-266 
    ISSN: 0886-9383
    Keywords: Principal factor analysis ; Factor analysis ; Eigenvalue analysis ; Multivariate analysis ; Weighted factor analysis ; Procrustean analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two approximate methods for weighted principal components analysis (WPCA) were devised and tested in numerical experiments using either empirical variances (obtained from replicated data) or assumed variances (derived from unreplicated data). In the first (‘spherical’) approximation each data vector was assigned a weight proportional to the geometrical mean of its variances in all dimensions. The arithmetical mean of variances was used instead in the other approximation. Both the numerical experiments with artificial data containing random errors of various kinds (constant, proportional, constant plus proportional, Poisson) and the analysis of two sets of Raman spectra clearly indicated the necessity of introducing statistical weights. The spherical approximation was found to be slightly better than the arithmetical one. The application of statistical weighting was found to improve the performance of PCA in estimation problems.
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  • 47
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 48
    ISSN: 0886-9383
    Keywords: Predictive ability ; Regression ; PLS ; SDEP ; Cross-validation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The standard deviation of prediction errors (SDEP) is used to evaluate and compare the predictive ability of some regression models, namely MLR, ACE and linear and non-linear PLS, the last being the best one. The parameter is determined by a cross-validation approach as an average of several runs obtained on forming groups in a random way. The variation in SDEP with the number of latent variables in PLS is also discussed.
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    Journal of High Resolution Chromatography 15 (1992), S. 840-842 
    ISSN: 0935-6304
    Keywords: UV detection ; Fluorescence detection ; FID ; Mass spectrometry ; Air pollution ; Chlorine ; 1-Chloro-2-naphthol ; 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 15 (1992), S. 827-833 
    ISSN: 0935-6304
    Keywords: GC ; Lubricating Oil ; Polycyclic aromatic hydrocarbons (PAH) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Liquid - liquid extraction with N-methyl-2-pyrrolidone, combined with solid-phase extraction on silica gel using n-pentane and dichloromethane as solvents, has been used for the isolation and concentration of the aromatic fraction from lubricating oil.The identification of individual compounds in this aromatic fraction was performed by capillary gas chromatography-mass spectrometry (CGC-MS) and by determination of retention indices. Quantitative results were obtained by flame ionization detection (CGC-FID). Eighty four compounds, predominantly naphthalenes, phenanthrenes, biphenyls, fluorenes, dibenzo-thiophenes, and their alkylated derivatives, have been identified in a commercial lubricating oil. The total amount of the aromatic fraction did not exceed 0.04 % of the oil.
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    Journal of High Resolution Chromatography 15 (1992), S. 834-836 
    ISSN: 0935-6304
    Keywords: Static headspace ; Optimization of conditions ; Gas chromatography ; Blood alcohol ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The precision and sensitivity of head-space GC can be improved by careful selection of the operating conditions: partitioning in the vapor phase can be promoted by altering the sample matrix; the ratio of the volumes of the gaseous and liquid phases, the sample temperature, the equilibration time, and the effect of sample mixing should also be considered.Most of the principles covered here can be applied to either manual headspace GC or to headspace GC utilizing an automated sampler.
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    Journal of High Resolution Chromatography 15 (1992), S. 30-32 
    ISSN: 0935-6304
    Keywords: Capillary zone electrophoresis ; Ionization constants ; Aromatic amines ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Capillary zone electrophoresis in untreated fused silica capillaries has proved suitable for the determination of the ionization constants of weak electrolytes. Several fundamental equations relating the electrophoretic mobilities of ionized solutes to hydronium ion concentrations in the running electrolyte have been verified experimentally. The observed dependence of the electrophoretic mobilities of weak bases and ampholytes on the pH of the electrolyte showed good agreement with predicted behavior. The pKa values calculated from electrophoretic mobility data obtained by capillary zone electrophoresis were reasonably close to those reported in the literature.
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    Journal of High Resolution Chromatography 15 (1992), S. 36-39 
    ISSN: 0935-6304
    Keywords: GC ; Signal averaging ; Detection limit ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ensemble or signal averaging has been used to increase detection limits in gas chromatography. The sample is injected several times into a gas chromatograph and the chromatograms generated are summed. The resulting chromatogram is treated as a separate chromatogram with the benefit of an improved signal-to-noise ratio. Use of the technique enables reliable quantitation, the time invested being used to convert an unacceptable signal-to-noise ratio into useful data. A discussion and some applications of the technique are described.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 15 (1992), S. 41-42 
    ISSN: 0935-6304
    Keywords: HPLC ; Ion exchange ; Volatile mobile phases ; Nucleotides ; 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 15 (1992), S. 61-61 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 15 (1992), S. 171-175 
    ISSN: 0935-6304
    Keywords: Coupled LC-GC-MS ; Loop interface ; Concurrent cosolvent evaporation ; Micro-LC ; Donor-acceptor complexes ; Fossil fuels ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A multidimensional LC-GC-MS system was developed and used to analyze complex fossil-fuel samples. The electron-acceptor stationary phase, 5 μm 2,4-dinitrophenylmercaptopropylsilica, was packed into a 0.32-mm × 350-mm microcapillary liquid chromatography (μLC) column. Aromatic fractions eluted from the μLC system at 12 μL/min and were diverted to the gas chromatograph mass spectrometer (GC-MS) by a ten-port switching valve with 50 and 7.6-μL loops. Concurrent cosolvent evaporation occurred in a 0.32-mm × 3-m precolumn ahead of a 0.25-mm × 30-m DB-5 analytical column. Solvent vapors exited through an open-split interface. The utility of the μLC-GC-MS system was demonstrated through the analyses of solvent refined coal, kerosene, and crude oil.
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  • 58
    ISSN: 0935-6304
    Keywords: Enantioselective gas chromatography ; 2,3-Diacylated cyclodextrins ; Chiral flavor analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclo -dextrin proves to be a versatile chiral stationary phase for the direct differentiation of aroma-relevant enantiomers.
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    Journal of High Resolution Chromatography 15 (1992), S. 180-183 
    ISSN: 0935-6304
    Keywords: GC ; Packed glass capillary column ; Gas analysis ; C1—C4 hydrocarbon analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new type of packed glass capillary column (PGCC) with a core, and its potential usage in practice are described. The permeability of the column is considerably greater than that of conventional PGCC and its N/(Pi-Po) value is also higher. This novel PGCC column has been successfully applied to the analysis of trace levels of ethyne, cyclopropane, propadiene, propyne, and other C1—C4 impurities in pure ethene, propene, 1,3-butadiene, and catalytic cracking gas samples as well as other petrochemical gases such as liquified petroleum gas.
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    Journal of High Resolution Chromatography 15 (1992), S. 184-189 
    ISSN: 0935-6304
    Keywords: Enantioselective gas chromatography ; Cyclodextrin derivatives ; Monoterpene hydrocarbons ; Essential oils ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using a dual column gas chromatograph equipped with two capillary columns coated with heptakis(6-O-methyl-2,3-di-O-pentyl)-β-cyclodextrin (6-me-2,3-pe-β-CD) and octakis(6-O-methyl-2,3-di-O-pentyl)-γ-cyclodextrin (6-me-2,3-pe-γ-CD), respectively, all important olefinic monoterpene hydrocarbons occurring in essential oils, including α-thujene, α- and β-pinene, camphene, sabinene, α- and β-phellandrene, Δ-3-carene and limonene can be resolved into enantiomers. With the chromatographic system described the characteristic enantiomeric composition of these monoterpene hydrocarbons in essential oils can be determined.
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  • 61
    ISSN: 0935-6304
    Keywords: Honey ; Free amino acids ; Capillary gas chromatography ; Heptafluorobutyryl isobutyl esters ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemical analysis of honey tends to concentrate on factors related to its state of preservation, e.g. HMF, diastase activity, and water content. Although there is no characteristic of honey officially regarded as suitable for certification of its botanical origin, literature is available in which several of the “minor” components of honey, such as flavors, di- and trisaccharides, and free amino acids, have been used to certify the botanical origin of the product.In this paper, six kinds of honey from different botanical sources (acacia, citrus fruit, chestnut-tree, rhododendron, rosemary, and lime-tree) were analyzed by capillary gas chromatography, and the data obtained evaluated statistically to determine whether the amino acid profile could be used to verify the botanical source of the material.The results have shown that the presence of amino acids such as arginine, tryptophan, and cystine is characteristic of a particular kind of honey, and that others, such as proline, asparagine, lysine, and methionine, can be used for discrimination if quantitative data is available about the levels of the compounds present.Evaluation of optimum split ratio for amino acid determination, and problems concerning the derivatization process, are also discussed.
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    Journal of High Resolution Chromatography 15 (1992), S. 195-198 
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Surface ionization detection (SID) ; Midazolam ; Human plasma ; Simple extraction ; 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 15 (1992), S. 190-194 
    ISSN: 0935-6304
    Keywords: Split injection ; Sample evaporation during injection ; Heat consumption during evaporation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: During sample evaporation in conventional vaporizing injection, the supply of heat to the evaporating liquid is a problem, first because the amounts of heat consumed are relatively large and, secondly, because the heat must be transferred to the sample within a very short time. Times available for evaporation, required amounts of heat, possible sources of heat, and the time required to transfer the heat to the sample liquid are discussed. It is shown that mixing with carrier gas contributes little heat to the evaporation process, but also that packings with glass wool have too low a heat capacity to deliver the required amount of heat to the evaporating sample. Transfer of heat from the insert wall to the sample easily requires several seconds, even if cooling of the vaporizing zone by 20° is accepted. Thus “flash evaporation” is usually impossible and most liquids must be held in the vaporizing chamber to allow full evaporation.
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    Journal of High Resolution Chromatography 15 (1992), S. 198-200 
    ISSN: 0935-6304
    Keywords: Micellar electrokinetic capillary chromatography ; Capillary electrophoresis ; Nitroaromatics ; 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 15 (1992), S. 201-203 
    ISSN: 0935-6304
    Keywords: Capillary zone electrophoresis ; Sample collection ; Preparative separation ; 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 15 (1992), S. 207-208 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 15 (1992), S. 203-205 
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    Keywords: Capillary gas chromatography ; SIM-MS ; Ethyl carbamate ; Wine ; Continuous extraction ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of High Resolution Chromatography 15 (1992), S. 206-206 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 15 (1992), S. 209-209 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 15 (1992) 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of High Resolution Chromatography 15 (1992), S. 227-234 
    ISSN: 0935-6304
    Keywords: High temperature gas chromatography ; Supercritical fluid chromatography ; Simulated distillation ; High boiling waxes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Simulated distillation boiling range distributions have been compared for high boiling petroleum wax samples using high temperature gas chromatography and supercritical fluid chromatography. Midpoint (50 % off) temperature differences were small, and average differences between the two types of analyses were less than 6° Details of optimization of the HTGC and SFC systems and injection techniques used are reported.
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    Journal of High Resolution Chromatography 15 (1992), S. 213-218 
    ISSN: 0935-6304
    Keywords: High resolution capillary gas chromatography (HRCGC) ; Single column capillary GC ; Isothermal and temperature programmed GC ; Analysis of multi component hydrocarbon mixtures ; One and two ring aromatic compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The scope of the principal techniques employed for the analysis of hydrocarbon mixtures is discussed, with emphasis on the analysis of one and two ring aromatic compounds by single column capillary gas chromatography. The paper considers both the column and the selection of the temperature regime (isothermal and temperature programmed). Much space is devoted to the characterization of the compounds by means of retention data.
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    Journal of High Resolution Chromatography 15 (1992), S. 235-237 
    ISSN: 0935-6304
    Keywords: Capillary GC ; Flame photometric detection (FPD) ; Response characteristics ; Organophosphorus pesticides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular emission of heteroelements such as phosphorus and sulfur is the basis of the selective response of the flame photometric detector. The behavior of the FPD towards phosphorus compounds has been studied and design improvements sought with regard to burner configuration and temperature distribution. The possibility of differentiating between compounds containing phosphorus atoms and those containing both phosphorus and sulfur atoms has also been examined.Detection limits and response characteristics have been reported for organophosphorus pesticide residues in samples of natural origin
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    Journal of High Resolution Chromatography 15 (1992), S. 219-226 
    ISSN: 0935-6304
    Keywords: HPLC ; Triacylglycerols (triglycerides) ; Oenothera ; Borago ; Ribes ; Primula ; Sapium ; γ-Linolenic acid (18:3 ω 6) [506-26-3] ; Estolides ; Stillingia oil ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reversed phase HPLC with short wavelength UV detection is a useful alternative to conventional separation systems, with RI detection, for the analysis of the triacylglycerols of highly unsaturated vegetable oils, including γ-linolenic acid-containing oils and technical drying oils.γ-Linolenic acid-containing triacylglycerols can be identified and separated from their α-linolenic analogs. The triacylglycerol fingerprints obtained by this technique from many γ-linolenic acid-containing oils and technical oils are highly characteristic, as is apparent from chromatograms obtained from the seed oils of Oenothera biennis, Borago officinalis, Ribes nigrum, Primula florindae, and Sapium sebiferum. Characteristic peak area ratios aid the identification of these oils, and estolide peaks are seen in Sapium seed kernel oils.The high detector response for triacylglycerols containing linoleate and/or linolenate residues may present additional advantages, e.g. in the detection of such triacylglycerols in olive oil.
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    Journal of High Resolution Chromatography 15 (1992), S. 249-255 
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Narrow bore columns ; Separation of chlorobiphenyl congeners ; Relative retention times ; Multidimensional gas chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Retention times of fifty one important chlorobiphenyl congeners have been determined on seven narrow bore GC columns coated with different stationary phases. The retention times of the chlorobiphenyls relative to tetrachloronaphthalene were plotted for different column combinations; the plots generated can be used to choose an optimum column combination for the multidimensional gas chromatographic separation of the chlorobiphenyls.
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  • 76
    ISSN: 0935-6304
    Keywords: Capillary GC ; On-line extractive alkylation ; On-line acylation ; Carboxylic acids ; Amines ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Gas chromatographic procedures are described for the determination of carboxylic acids and chlorinated anilines in water samples.Propionic acid and 2,6-difluorobenzoic acid in aqueous solution have been simultaneously alkylated and extracted by means of a continuous two-phase reaction system, and then quantitated by on-line coupled capillary gas chromatography; tetrahexyl-ammonium hydrogen sulfate was used as phase transfer catalyst and pentafluorobenzyl bromide as reagent.A factorial design approach was used to optimize on-line derivatization of aqueous propionic acid with regard to pH and concentration of phase transfer catalyst. Alkylation and extraction, under optimized conditions, followed by quantitation of the pentafluorobenzyl ester by flame ionization detection furnished a linear calibration for concentrations between 0.1 and 10 μg/ml. The relative standard deviation was 9-15 %.The continuous two-phase reaction system was also used to determine (chlorinated) anilines present in water at concentrations of 0.1-1 μg/ml; pentafluorobenzoyl chloride was used as reagent and analysis was performed by capillary gas chromatography with flame ionization or electron capture detection. The on-line acylation of p-chloroaniline was optimized with regard to pH, reagent concentration, and reaction time.The on-line reaction system worked satisfactorily for both applications, although excess reagent caused some problems with the chromatography.
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  • 77
    ISSN: 0935-6304
    Keywords: Microcolumn liquid chromatography ; Enantiomeric separation ; Micellar mobile phase ; Bile acid derivatives ; 1,1′-Binaphthyl-2,2′-diyl-hydrogen phosphate ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 78
    ISSN: 0935-6304
    Keywords: Capillary GC ; Polychlorobiphenyls (PCB, ClxB) ; Polychlorodibenzodioxins (PCDD, ClxDD) ; Polychlorodibenzofurans (PCDF, ClxDF) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High resolution gas chromatography, with mass selective detection, has been used for the analysis of PCB on methyl 50 % octyl polysiloxane (SB 50 Octyl), methyl octadecyl polysiloxane, and a smectic polysiloxane (SB Smectic); and for the analysis of polychlorodibenzodioxins and polychlorodibenzofurans with 1 to 8 chlorine substituents on 100 % cyanopropyl siloxane (SP 2331), smectic polysiloxane (SB Smectic), a new polar stationary phase (DB-Dioxin). The analysis has also been performed by column coupling.
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  • 79
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    Journal of High Resolution Chromatography 15 (1992), S. 277-278 
    ISSN: 0935-6304
    Keywords: Synthetic phospholipids ; Reversed phase chromatography ; Anomalous retention behavior ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 80
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    Journal of High Resolution Chromatography 15 (1992), S. 281-281 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 81
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    Journal of High Resolution Chromatography 15 (1992), S. 417-422 
    ISSN: 0935-6304
    Keywords: Ion mobility spectrometry (IMS) ; Ion mobility detection (IMD) ; Capillary GC ; Capillary SFC ; Liquid Chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ion mobility monitoring has been used for detection in gas, supercritical fluid, and liquid chromatography, illustrating its potential as a method of detection for unified chromatography. Applications presented include GC-IMD of dioxins in fly ash, SFC-IMD of vitamin E, and HPLC-IMD of alkylamines.Ion mobility spectra of several mixed supercritical fluid mobile phases are also presented. Use of methanol, acetonitrile, and dichloromethane as modifiers of supercritical carbon dioxide, and use of supercritical dichlorodifluoromethane and chlorodifluoromethane as mobile phases had little effect on the reactant ion pattern at the flow rates and concentrations used in this study. Only when acetone was used as a modifier of carbon dioxide did the positive reactant ions change significantly. No effect of modifiers or mobile phase was observed for the negative reactant ions.
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  • 82
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    Journal of High Resolution Chromatography 15 (1992), S. 428-433 
    ISSN: 0935-6304
    Keywords: Capillary GC ; Serially connected capillary columns ; Wide bore open tubular columns ; Industrial solvents ; Prediction of retention times ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas chromatographic separation of the components of a complex mixture of industrial solvents, not possible on a single stationary phase owing to coelution of some of the compounds, has been achieved on two serially connected wide bore capillary columns of different polarity.The analysis of a mixture of twenty five compounds was optimized using the serial gas chromatography theory of Purnell and Williams. The capacity factors of sample components measured with the two columns coupled in series were found to agree with those predicted by theory, regardless of the order in which they were connected.
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  • 83
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    Journal of High Resolution Chromatography 15 (1992), S. 423-427 
    ISSN: 0935-6304
    Keywords: Optimized post-column derivatization ; Xylenol orange - cetylpyridinium bromide ; Highly sensitive detection ; Lanthanides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rare earth elements have been separated by HPLC on octadecyl-bonded silica gel, dynamically modified with ammonium dodecylsulfate, using aqueous solutions of α-hydroxyisobutyric acid as mobile phase.The requirements and characteristics of post-column reaction with xylenol orange and cetylpyridinium bromide were investigated and optimized, and the reaction found to be highly sensitive and sufficiently rapid. The absorbance of the complex at 598 nm was not affected by the presence of α-hydroxyisobutyric acid at concentrations of the latter up to 150 mmol/l; at higher concentrations of the acid, the absorbance decreased slightly.For most of the rare earth elements the response was linear up to 0.2 mmol/l; the relative standard deviation of peak area was, typically, ∼1 %. The sensitivity of the method was usually better than 1 μg/ml.The results obtained from the determination of lanthanum, cerium, praseodymium, and neodymium in samples of apatite and bastnesite were in a good agreement with those obtained by ICP-AES.
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  • 84
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    Journal of High Resolution Chromatography 15 (1992), S. 434-436 
    ISSN: 0935-6304
    Keywords: Micropacked LC ; Dry-packing method ; Column technology ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A dry-packing method has been developed which enables the preparation of packed capillary columns for micro HPLC from 250 μm i.d. tubing and 5 μm packing materials. Pressurized gases, such as hydrogen and argon, were used to transport the packing media, and ethanol or methanol were used as discharge agents. By changing the gas pressure, the packing density could be easily adjusted. It was found that, within experimental limits, the higher the packing density, the greater the column efficiency. Comparison between dry- and slurrypacked columns showed that the former had greatly improved stability; the efficiency of dry-packed columns was about the same as, or even better than, that obtained by slurry-packing.
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  • 85
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    Journal of High Resolution Chromatography 15 (1992), S. 449-451 
    ISSN: 0935-6304
    Keywords: GC ; Signal averaging ; Microbore columns ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ensemble or signal averaging, and the use of the technique for the solution of some unique problems with minimum sample handling, have previously been reported. The capability of the technique has been evaluated with microbore gas chromatography for the fast handling of a large number of analyses: ca 20-30 replicate injections are easily attainable in a reasonable analysis time. The implementation of the signal averaging technique with other concentration techniques for improving detection limits is also demonstrated.
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  • 86
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    Journal of High Resolution Chromatography 15 (1992), S. 444-448 
    ISSN: 0935-6304
    Keywords: Block polysiloxanes ; Block condensation ; Chiral polysiloxanes ; Functionalized polysiloxanes ; Polycondensation ; Polysiloxane stationary phase ; Reactive polysiloxanes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Exploitation of the full potential of selector-modified polysiloxanes as chromatographic stationary phases is limited because conventional methods of silicone synthesis involve strong acids or strong nucleophiles such as water or bases; under these conditions many potentially useful selectors decompose. The general approach to polysiloxane synthesis presented herein gives access to functionalized polysiloxanes under mild conditions. The functional groups incorporated can serve as chromatographic selectors or as electrophilic sites for secondary modification or cross-linking.
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  • 87
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    Journal of High Resolution Chromatography 15 (1992), S. 437-443 
    ISSN: 0935-6304
    Keywords: Coupled LC-GC ; Polycyclic aromatic hydrocarbons ; Automation ; Clean-up and analysis ; Lubricating oil ; Urban air ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A fully automated system, comprising a liquid chromatograph (LC) coupled on-line to a gas chromatograph (GC) by means of a loop interface, has been constructed for clean-up and analysis of polycyclic aromatic hydrocarbons (PAH). An autosampler was utilized for sample injection into the LC. By the use of a back-flush technique in conjunction with an ordinary analytical aminopropylsilica column, PAH could be isolated by LC: a concurrent solvent evaporation injection technique was then used for on-line transfer of the PAH fraction to the GC, where the PAH analysis was completed.Compared with ordinary off-line LC clean-up followed by GC analysis, the sensitivity has been increased by a factor of 50-100, yielding a detection limit for individual PAH of a few nanograms per sample when using flame ionization detection. Further, irreproducible losses of low molecular weight PAH as a result of solvent evaporation steps in off-line clean-up procedures have been eliminated. Reproducibility of retention times and relative peak areas is high, facilitating automatic peak identification and calculation of concentrations, and the system can thus be used for automatic sample evaluation. The total time required for clean-up and analysis is only 1.5 hours, and the demand on personnel time for the analysis of PAH has been drastically reduced.The technique has been demonstrated with samples of urban air and of used automobile engine lubricating oil.
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  • 88
    ISSN: 0935-6304
    Keywords: Capillary zone electrophoresis ; Surface modification ; Vinyl-derivatization ; Adsorption ; Polymer coating ; Polyvinylalcohol ; Proteins ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mixtures of several basic proteins have been used to test CZE capillaries with surfaces modified by new pretreatment procedures; the performance obtained has been compared with that achieved using capillaries treated by procedures described in the literature.It has been shown that addition of non-ionic polyvinylalcohols (PVA) to CZE buffer solutions deactivates even bare, i.e. untreated, fused silica surfaces and renders them suitable for separations of basic proteins. The performance obtained from such surfaces was comparable with that of capillaries modified by the more elaborate procedures of etching, silanol derivatization, and/or adsorptive coating (again with polymers).A home-made device is described which enables derivatization and coating reactions to be performed on fused silica capillaries under an inert atmosphere, i.e. one free from oxygen and water.
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  • 89
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    Journal of High Resolution Chromatography 15 (1992), S. 478-479 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Kováts retention index ; GW-BASIC program ; Computer-assisted calculation ; 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 15 (1992), S. 467-471 
    ISSN: 0935-6304
    Keywords: Capillary GC ; Medium pressure liquid chromatography ; Chemiluminescence nitrogen detector ; Acetonitrile ; Propionitrile ; Naphtha ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two methods have been developed for the determination of trace levels of acetonitrile and propionitrile in light naphthas. One involves clean-up and preconcentration by medium pressure liquid chromatography (MPLC) in which nitriles are concentrated ten-fold while the complex hydrocarbon matris is removed. The concentrated solution is then analyzed by high resolution GC with flame ionization detection. The second method involves direct injection of samples into a capillary GC equipped with chemiluminescence nitrogen detection.The results and repeatability obtained from both methods are comparable. Preconcentration enables identification by GC-MS and simultaneous analysis of other polar species, with no need for selective detectors. Direct analysis is, on the other hand, much less time-consuming and requires less sample.
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  • 91
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    Journal of High Resolution Chromatography 15 (1992), S. 458-466 
    ISSN: 0935-6304
    Keywords: SFC Pressure drop ; Efficiency ; Compressibility effects ; Analysis time ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of the pressure drop on the efficiency and speed of analysis in packed and open tubular supercritical fluid chromatography (SFC) is described: methods previously developed to describe the effects of mobile phase compressibility on the performance of open tubular columns in SFC have been extended to packed columns.The Horvath and Lin equation has been used to elucidate the influence of variations in velocity, diffusivity, and capacity factor along the column on the overall efficiency of packed column SFC. In packed columns, in contrast with the situation in open tubular columns, because the increase in velocity is no longer compensated by an increase in diffusion coefficients, the increase in both linear velocity and capacity factor which result from a significant pressure drop cause the plate height to increase along the column.The effect of fluid decompression along the length of the column on the speed of analysis in SFC has been studied and numerical expressions derived which enable calculation of compressibility correction factors for the plate height. Both the f1 and f2 correction factors remain very close to unity for acceptable pressure drops, which means that the pressure drop has virtually no effect on the number of plates generated per unit time for an unretained component. For retained species, the decompression of the mobile phase across the column causes the capacity factor to increase and hence leads to increased analysis times.
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  • 92
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    Journal of High Resolution Chromatography 15 (1992), S. 472-477 
    ISSN: 0935-6304
    Keywords: Headspace sampling techniques ; Capillary gas chromatography ; Detection techniques ; Volatile compounds ; Fresh fruit ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The composition of volatile compounds produced by fruit during growth and post-harvest storage and ripening has been studied and the different headspace methods compared. Static and dynamic headspace sampling have been compared and evaluated according to their capacity to collect and concentrate volatiles from the atmosphere surrounding the fruits, and FID, MSD, and organoleptic detection have been compared. The results emphasize that the headspace sampling procedure selected is crucial to the performance of subsequent analysis.
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  • 93
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    Journal of High Resolution Chromatography 15 (1992), S. 486-488 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 94
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    Journal of High Resolution Chromatography 15 (1992), S. 555-561 
    ISSN: 0935-6304
    Keywords: RPHPLC ; Prediction of retention time ; Quaternary mobile phase ; 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 15 (1992), S. 562-563 
    ISSN: 0935-6304
    Keywords: Reversed phase ; Variable wavelength ; Dye intermediates ; 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 15 (1992), S. 564-565 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 97
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    Journal of High Resolution Chromatography 15 (1992) 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 98
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    Journal of High Resolution Chromatography 15 (1992), S. 569-569 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 99
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    Journal of High Resolution Chromatography 15 (1992), S. 579-584 
    ISSN: 0935-6304
    Keywords: GC Analysis ; LC Analysis ; Preparative LC purification ; Syntheses ; Alkylated cyclodextrins ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methods of alkylation of α-, β- and γ-cyclodextrins have been optimized with regard to the parameters of reaction, degree of alkylation and yields. The analysis of the reaction mixtures and of the isolated single species has been performed by high temperature GC and HPLC. The phase systems of the preferably applied HPLC have been carefully adjusted by variation of both the stationary and mobile phases to the very different hydrophobicities of the various alkylated CD species which have been synthesized. Several partially or fully alkylated CD species were isolated from preparative scale HPLC separations in high purity.
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  • 100
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    Journal of High Resolution Chromatography 15 (1992), S. 573-578 
    ISSN: 0935-6304
    Keywords: Capillary zone electrophoresis ; Switchable electroosmotic flow ; Proteins ; Oligosaccharides ; Nucleotides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A surface modification has been developed which yields fused silica capillaries with switchable electroosmotic flow (anodal/cathodal). The capillary surface is a composite material consisting of unreacted silanol groups, a layer of positively charged quaternary ammonium functions, and a hydrophilic layer of long polyether chains. Because of the presence of positively and negatively charged groups, the net charge of the capillary surface can be varied from positive to negative by changing the pH of the running electrolyte, thus enabling manipulation of the magnitude and direction of the electroosmotic flow. The long polyether chains were effective in shielding biomacromolecules from the charged inner surface of the capillary, thus minimizing electrostatic interaction of the solutes with both unreacted silanols and the quaternary ammonium groups which had been introduced. As a consequence, high separation efficiencies were achieved with proteins, nucleotides, and a series of acidic oligosaccharides.
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