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Analytical and Bioanalytical Chemistry (v.359, #2)
Statistical comparison of calibration methods in multicomponent analysis by Matthias Otto (pp. 123-125).
Spectrophotometric multicomponent analysis is considerd on the basis of inverse multivariate calibration with linear methods (ordinary least squares, principal component, ridge and partial least squares regression) and with the non-linear methods ACE and the non-linear partial least squares. The performance of the different methods is compared by paired F-tests. As an estimate of the error variance the residual mean sum of squares in the analysis of variance table is used. The comparison is demonstrated for the infrared spectrometric analysis of the hydroxyl group content of brown coal measured in diffuse reflectance. Although the error variances among the calibration methods differ gradually, the differences are much less pronounced at statistical level.
Validation of a computer-program for the interpretation of infrared spectra by R. Salzer; S. Thiele; H. Thomas (pp. 126-131).
The capability of a modern interpretation system for IR spectra has been tested, in which the process of structural assignment is modelled by methods of fuzzy logic. Figures of merit were generated for different interpretation algorithms. These figures of merit permit the validation as well as a comparison of independent interpretation systems. The influence of the sample preparation practice onto the information content of the resulting spectrum has been evaluated as well. Automatically generated band tables show only restricted reliability.
Direct analysis of solid samples by graphite furnace atomic absorption spectrometry with a transversely heated graphite atomizer and D2-background correction system (SS GF-AAS) by R. Nowka; H. Müller (pp. 132-137).
An instrumental design for the analysis of heavy metals in solid samples (certified reference materials, river sediments, cements) by direct graphite furnace atomic absorption spectroscopy (SSGF-AAS) is presented and outlined. A high performance atomic absorption spectrometer with a D2-background corrector and a transversely heated graphite atomizer was modified. Solid sampling was achieved by a mechanical module combined with an ultra microbalance. Cadmium, lead and chromium in different samples (sample weights between 20–400 μg) have been determined in the μg/g- to ng/g-range with the graphite-platform technique. Different ways of calibration and inhomogeneity problems are discussed. The precision of SSGF-AAS is equal to the precision of the conventional AAS-technique with chemical digestion (microwave digestion system, Zeeman-AAS). It is shown that SSGF-AAS is a reasonable alternative to the conventional technique for selected analytical problems.
Analysis of N-dimensional data arrays from fluorescence spectroscopy of an intermediary sugar product by C. A. Andersson; L. Munck; R. Henrion; G. Henrion (pp. 138-142).
Unwanted formation of colour takes place during the production of crystalline sugar. The degree of colouration depends partly on the necessary processing conditions, e.g. heating and pH, and partly on the initial composition and condition of the sugar beets used as raw material. Reducing sugars are formed during the process. These are reactive compounds forming a variety of coloured complexes and strong precursors to further formation of colour and many of these compounds contain fluorophores. In the present work it is discussed if spectrofluorometric screening of intermediary sugar products prior to the final heating stages combined with a multi-way chemometric approach can provide information that significantly reflects the condition of the process and the beets. The model used is the N-way PCA (Principal Component Analysis) which is an exploratory model, not necessitating explicit modelling of single parameters nor any assumptions towards parameter interaction. By use of a 4-way PCA of order (3,2,3,3) satisfactory classification of 47 thick juice samples belonging to 5 factories has been obtained from a spectrofluorometric screening method. Also, a temporal trend has been found to evolve during the time of production. The investigation substantiates the use of modern models from data analysis for extracting significant information from large and complex data sets.
Classification of wine samples by means of artificial neural networks and discrimination analytical methods by Li-Xian Sun; Klaus Danzer; Gabriela Thiel (pp. 143-149).
The three-layer artificial neural network (ANN) model with back-propagation (BP) of error was used to classify wine samples in six different regions based on the measurements of trace amounts of B, V, Mn, Zn, Fe, Al, Cu, Sr, Ba, Rb, Na, P, Ca, Mg, K using an inductively coupled plasma optical emission spectrometer (ICP-OES). The ANN architecture and parameters were optimized. The results obtained with ANN were compared with those obtained by cluster analysis, principal component analysis, the Bayes discrimination method and the Fisher discrimination method. A satisfactory prediction result (100%) by an artificial neural network using the jackknife leave-one-out procedure was obtained for the classification of wine samples containing six categories.
Novel optical pH-sensor based on a boradiaza-indacene derivative by T. Werner; C. Huber; S. Heinl; M. Kollmannsberger; J. Daub; O. S. Wolfbeis (pp. 150-154).
A pH-optode is described based on 1, 3, 5, 7-tetramethyl-8-(4-dimethylamino)-4-difluorobora-3a, 4a-diaza-(s)-indacene (1) immobilized in a hydrogel matrix. Its uncharged form is non-fluorescent, whereas the protonated form displays strong emission. The quenching of the emission can be mechanistically explained by a PET (photoinduced electron transfer) from the dimethylamino group to the fluorophore. The perpendicular configuration at the C(8)-aryl bond contributes to the efficiency of the on/off-switching behavior. Incorporation of the dye into a hydrogel matrix results in a transparent sensor membrane which can be used to measure the pH in the range of 1-3. The sensor shows high signal intensity, good reproducibility, and the response characteristic is stable over hours of operation even at low pH-values.
Development of an automated bacterial luminescence test for biomonitoring of environmental contaminants by G. Schwedt; Christian Reiter; Rolf Uthemann; Elmar Grabert (pp. 155-160).
The development of the bacterial luminescence test to an automated biomonitor is described. The computer controlled system was optimized by varying the following parameters: intermixture of the analyte solution and bacteria suspension, intensity and period of stirring during intermixture, delay time for temperature equalization, long-time stability of the bacteria and evaluation of the measured signals. All measurements were carried out using organic and inorganic pollutants, e.g. formaldehyde, phenol, 2,4-dichlorophenol, cyanide and lead ions. Five-minute inhibition curves from a number of single runs are presented.
Size and phase fractionation of water components by membrane filtration Distribution patterns for arsenic, iron and manganese in aqueous effluents of tin ore settling plant by R. Wennrich; J. Mattusch; P. Morgenstern; T. G. Dzherayan; V. M. Shkinev; B. Y. Spivakov (pp. 161-166).
The possibility of on-line membrane size-fractionation of water components and simultaneous separation of particulate and dissolved matter at each filtration stage has been shown. The distribution patterns have been studied for As, Fe and Mn in effluent samples of tin ore tailings (Altenberg, Saxony, Germany). The seepage composition is characterized by high concentrations of Fe and As. The particulate and dissolved components were separated in five fractions between 0.025 and 8 μm. It was suggested that the distribution patterns of As and Fe compounds depend on the chemical conditions at the sampling sites. Manganese exists mainly in solvated forms in the liquid fractions.
Quantification of partial structures of aquatic humic substances by 1H-NMR under WATR conditions by H. Herzog; S. Haiber; P. Burba; J. Buddrus (pp. 167-170).
Aquatic humic substances (HS) isolated from surface water, leakage water and ground water have been investigated by 1H-NMR. The overlapping HOD signal was eliminated by adding ammonium chloride and applying the multiecho method CPMG (Carr, Purcell, Meiboom, Gill) under WATR conditions (water attenuation by transverse relaxation) permitting quantification of partial structures of HS. The proportion of carbohydrates/alcohols/ethers decreases and the proportion of alkyl moieties increases with increasing water or soil depth and thus microbial diagenesis. Also, increasing deoxygenation of aromatic substituents is observed with increasing water or soil depth. In some cases, elimination of the NMR signal of HOD is accompanied by the appearance of another HOD signal which is slightly shifted and much smaller in intensity; this signal probably results from water strongly bound by hydrogen bonding within the HS macromolecules.
Determination of total chromium in terrestrial and marine samples by electrothermal atomic absorption spectrometry after pressure digestion by Sunil Jai Kumar; Peter Ostapczuk; H. Emons (pp. 171-175).
A comparison between two commonly used sample digestion procedures was performed for the determination of total chromium in biological matrices. Ten reference materials (terrestrial and marine matrices) have been digested in HNO3, HNO3 + HClO4 and HNO3 + HF, respectively, under pressure in quartz vessels of a high pressure asher (HPA) or in PTFE bombs with external heating. Much lower chromium values than expected were obtained in most of the reference materials by using quartz vessels with nitric acid because of adsorption of chromium at quartz surfaces. Determinations after sample digestion in PTFE vessels with external heating showed expected results, except in some reference materials which precipitated more silica. An improvement of the results was observed by using a mixture of nitric acid and perchloric acid, but only the combination of nitric acid and a small amount of HF provided the desired results in all the reference materials studied.
HRGC-MS of polychlorinated phenanthrenes (PCPhen), dibenzothiophenes (PCDT), dibenzothianthrenes (PCTA), and phenoxathiins (PCPT) by T. Wiedmann; U. Riehle; J. Kurz; K. Ballschmiter (pp. 176-188).
Polychlorinated phenanthrenes (PCPhen, Clx Phen, x = 1–10), dibenzothiophenes (PCDT, ClxDT, x = 1–8), thianthrenes (PCTA, ClxTA, x = 1–8), and phenoxathiins (PCPT, ClxPT, x = 1–8) were synthesized and analyzed by high resolution capillary gas chromatography and EI and NCI mass spectrometry. In experiments the formation of polychlorinated phenanthrenes and dibenzothiophenes in combustion processes has been proved and compounds of these two classes have been detected in dust samples of an urban motorway tunnel.
Volatile organic compounds in urban atmospheres: Long-term measurements of ambient air concentrations in differently loaded regions of Leipzig by T. Knobloch; A. Asperger; W. Engewald (pp. 189-197).
For the comprehensive characterization of ambient air concentrations of a broad spectrum of volatile organic compounds (VOCs) an analytical method is described, consisting of adsorptive enrichment, thermal desorption without cryofocusing, and capillary gas chromatographic separation. The method was applied during two-week measuring campaigns in winter and summer 1995, and in the winter of 1996. Long-term sampling was carried out at sampling points in residential areas in the suburbs and near the city center of Leipzig. About 70 VOCs – mainly hydrocarbons from propene to hexadecane – were identified both by GC-MS and chromatographic retention data and quantified after external calibration. Mean values of VOC concentrations obtained during the sampling periods are reported and discussed with regard to the topographical location of the sampling points in the Leipzig area, seasonal variations, and possible emission sources.
Determination of the electrophoretic mobility of bacteria and their separation by capillary zone electrophoresis by Alexander Pfetsch; T. Welsch (pp. 198-201).
Conditions for the determination of electrophoretic mobilities of bacteria by capillary electrophoresis (CE) were explored. Most precise values are obtained using fused silica capillaries of 1–3 m length (0.25 mm inner diameter), a background buffer with an ionic strength of 0.0015 mol/L and a pH value of 7–10 at a field strength of 120 V/cm. Capillary electrophoretic separation of three different bacteria populations on the basis of their mobility differences could be realized. Electrophoretic band widths of all bacteria populations investigated are relatively large compared to molecule bands. It finds its explanation in the different distribution of surface charge density to cross-sectional area of each single cell of a population.
Determination of Triton X-100 in influenza vaccine by high-performance liquid chromatography and capillary electrophoresis by Katja Heinig; C. Vogt (pp. 202-206).
Triton X-100 is applied to influenza vaccines at different stages of the manufacturing process to prevent aggregation and precipitation of biomolecules. Furthermore it is used to disintegrate the virus particles in split vaccine and to guarantee the homogeneity during production and utilisation. The final concentration of Triton X-100 has to be determined because the concentration changes in manufacturing process. The determination of the total amount of Triton X-100 as well as the separation of its ethylene oxide oligomers was possible with high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). In HPLC a change of the column and eluent was necessary, in CE different electrolytes were used for the various separation effects. The HPLC method for the analysis of total Triton was preferred for the quantification of Triton X-100 in influenza vaccine because of better linearity, reproducibility and detection sensitivity compared to CE. In the end products an average concentration of 0.117 mg/mL was found.