Improvement of analyte to interferent line intensity ratio in direct current glow discharge mass spectrometry

Elemental analysis by quadrupole mass spectrometry with direct current powered glow discharge ion source has been improved for flat Cu samples. The line ratio of analyte to Ar-related interferents can be enhanced for several orders of magnitude when ion source geometry, ion extraction system and operating parameters are optimised quasi-simultaneously. Such an extreme improvement may partially be explained by different ion energy distributions depending on their origin: matrix and analytes, working gas, residual gases. Probably it is due to a synergistic effect of several processes needing further investigation.     

Laser-induced fluorescence study of the hydrogen atom formation dynamics in the 248 nm gas-phase photodissociation of vibrational state selected water (H<Subscript>2</Subscript>O (|04<Superscript>−</Superscript>〉))

The vibrationally-mediated H₂O gas-phase photodissociation was studied at a photolysis wavelength of 248 nm. Single rotational states of the |03⁻〉|2〉 and |04⁻〉 H₂O overtone vibrations were prepared by laser photoexcitation around 720 nm. H atoms formed in the photodissociation of the H₂O (|04⁻〉 = 3₁₃) were detected by Lyman-α laser-induced fluorescence spectroscopy with sub-Doppler resolution to determine their translational energy. The present result confirms that in the dissociation process the major part (ca. 93%) of the available energy is released as relative translational energy of the nascent H + OH photofragments, in agreement with earlier complementary measurements (R. L. Vander Wal, J. L. Scott and F. F. Crim, J. Chem. Phys. 94, 1859 (1991)), where the internal excitation of the OH product radical was investigated at different photolysis wavelengths.     

Quantitative determination of oxocarboxylic and hydroxycarboxylic acids in normal individuals and ketoacidotic patients

Oxo- and hydroxycarboxylic acids as metabolites of valine, leucine, and isoleucine and of ketogenesis are simultaneously quantitated in the form of their methyl esters and methyl esters/O-methyloximes by gas chromatography using internal and external standards. Normal values for the urinary excretions of the amino acid metabolites are between 3 ± 2 μmol/24 h (mean value ± standard deviation) for 2-oxoisocaproic acid and 122 ± 58 μmol/24 h for 3-hydroxyisobutyric acid. In diabetic ketoacidosis the values are increased by a factor of 2-10.     

Characterization of the chemical homogeneity of solid-state standard materials by chemometric methods

Summary For characterizing the homogeneity of a copper standard for optical emission spectrometry, the results of spark source mass spectrographic (SSMS) milliprobing have been treated by diverse chemometric methods. The proposed strategy includes visualization of the data, global homogeneity testing for each element, testing the anisotropy of elemental distributions, search for correlation between elements, and statements on the homogeneity with respect to other analytical procedures. The copper standard was proved to be non-homogeneous for SSMS but homogeneous for techniques of optical emission spectroscopy having larger sampling volumes.

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Homogenitätscharakterisierung fester Standardproben unter Verwendung chemometrischer Methoden

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Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday     

Basic profiles of organic acids in urine

Altogether 143 of the organic acids regularly occurring in urine of healthy individuals are identified as methyl esters by gas chromatography-mass spectrometry with respect to their complete chemical structures. They are classified as dicarboxylic acids, oxocarboxylic acids, hydroxycarboxylic acids, aromatic acids, furancarboxylic acids, nitrogen-containing acids and acid conjugates. By pre-fractionating the complex mixture of the total organic acids, peak overlap is minimized, and substances in low concentrations can also be detected and identified. The qualitative patterns of the urinary organic acids in the fractions are constant and reproducible, and in many cases a reliable identification of organic acids is possible by gas chromatography alone, using methylene units and separation on OV-1701 capillary columns.     

Routine serum protein analysis by capillary zone electrophoresis: Clinical evaluation

Summary To measure the five classical protein fractions in human serum several electrophoretic techniques are available. Besides separation on cellulose acetate membrane or agarose gel, capillary zone electrophoresis (CZE) may be a useful analytical alternative in clinical routine. We have compared the Dionex CES I capillary electrophoresis system with that of the Olympus Fractoscan using specimens submitted for routine analysis. For clinical evaluation 102 samples from patients with various diseases have been analysed. Serum protein fractions were judged on separation performance, precision and the regression method ofBablok-Passing. Regression analysis revealed variable agreement between both methods with a slope ± intercept of 2.10–0.52 (α₁-fraction) and 1.0–0.20 (α₂-fraction) as worse and best, resectively; and the coefficient of variation of migration time: 5.9 %–6.8 % (between-run imprecision). Differences in the comparison of fractions are mainly caused by the improved resolution of CZE; e.g. one β-globulin peak on cellulose acetate is separated into two distinct protein fractions in CZE, including more detailed diagnostic information—as is also the case with γ-fraction. In some cases monoclonal gammopathy with low concentrations of immunglobulin clone can only be detected in CZE, whereas the cellulose acetate membrane (CAME) electropherogram is inconspicuous. The within-run precision (N=18) gave coefficients of variation of peak areas 1.3–5.9 % (CZE) and 1.0–3.8 % (cellulose acetate membrane). This is the first time that a complete clinical evaluation of CZE serum protein fraction analysis has been performed. CZE with its higher resolution and hence more detailed diagnostic information in some cases, showed good separation patterns, precision and correlation. Interchangeability of results showed that this CZE method is well suited for analysis of serum protein fractions in clinical routine. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996.     

Aalysis of the fatty acid composition of the lipid classes in human blood serum under normal diet and when supplemented with fish oil

Total lipids have been extracted from human serum with chloroform–methanol 2:1 (v/v) and separated into individual classes by TLC. After transesterification the fatty acid methyl esters were analyzed by capillary gas chromatography on an FFAP column. The quantitation of ω-3 fatty acids has been performed using internal and external standards. Internal lipid standards for each lipid class were carried throughout the entire analytical procedure. Under normal diet eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are incorporated into the lipid classes to different extents: cholesterol esters; EPA, 6.5 ± 1.9 γ/ml serum; DHA, 4.3 ± 1.9 μg/ml: phospholipids; EPA, 5.9 ± 2.7 μg/ml; DHA, 31.8 ± 8.1 μg/ml. Fish oil supplementation leads to a 4 to 6-fold rise in EPA and to an approximately 2-fold rise in DHA.