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Analytical and Bioanalytical Chemistry (v.361, #1)
Inverse calibration predicts better than classical calibration by V. Centner; D. L. Massart; S. de Jong (pp. 2-9).
The study shows that in the classical calibration situation inverse calibration, i.e. concentration = f(measurement) yields more reliable predictions than classical calibration, i.e. measurement = f(concentration). The theoretical proof is verified by Monte Carlo simulations and by two practical examples. The improvement due to the use of inverse calibration increases with decreasing precision of the measurements.
Multivariate geostatistical analysis of soil contaminations by J. W. Einax; U. Soldt (pp. 10-14).
Soil is one of the most endangered compartments of our environment. The input of pollutants into the soil caused by industrial production, agriculture, and other human activities is a problem of high relevance. A contour analysis of soil contamination is the first step to characterize the size and magnitude of pollution and to detect emission sources of heavy metals. The evaluation and assessment of the large number of measured samples and pollutants require the use of efficient statistical methods which are able to discover both spatial and multivariate relationships. The evaluation of the presented case study – soil contamination by heavy metals – is carried out by means of multivariate geostatistical methods, also described as theory of linear coregionalization. Multivariate geostatistics connects the advantages of common geostatistical methods (spatial correlation) and multivariate data analysis (multivariate relationships). In the given case study of soil pollution by heavy metal emissions it is excellently possible to detect multivariate spatial correlations between different heavy metals in the soil and to determine their common emission sources. These emission sources are located in the area under investigation.
Simultaneous simplification of loading and core matrices in N-way PCA: application to chemometric data arrays by René Henrion (pp. 15-22).
In the Tucker3 model of N-way principal components analysis (NPCA), a so-called core matrix describes the possible interactions between components from different modes. For an easy interpretation of solutions, it is necessary to have as few interactions as possible (in conventional PCA of data tables, such interactions can always be avoided). This goal may be realized by various approaches of core matrix transformations. At the same time, it is desirable to have simple component (or loading) matrices. Usually, the simplicity of the core conflicts to a certain degree with the simplicity of the components. The paper demonstrates how the conditional optimization of both goals can be used to find a compromise. For the purpose of illustration, the procedure is first applied to a small three-way data array from heavy metal analysis of tissues in different samples of game. Later, a data array of bigger size from a three-way interlaboratory study is considered.
Application of formal concept analysis to structure-activity relationships by H.-G. Bartel; Rainer Brüggemann (pp. 23-28).
An alternative method to perform structure activity relationships will be presented. This method is based on Discrete Mathematics, i.e. on concept lattice theory. Exploring a chemical data matrix, this mathematical method allows the derivation of “if-then”-rules. For example it can be hypothesized that a specific chlorinated alkane will pose a high toxic potential towards algae and will have a slight tendency for volatilization. 1997 / Accepted: 5 January 1998
Basic experimental studies on the operation of photoionization detectors by Steffen Mergemeier; Ingo Ebner; F. Scholz (pp. 29-33).
Commercially available and self-made photoionization detectors have been studied in a simple flow manifold without chromatographic column. The self-made detector allowed the independent variation of the detector volume, the electrode surface area and a selective irradiation of the anodes and cathodes. The photoionization of ethanol and acetone has been measured in hydrogen as carrier gas. All experimental results were consistent with a model based upon a photoionization proceeding in the adsorption layer of the electrodes as the main signal generating process. It has been shown that the photoionization of molecules in the gas phase plays only a marginal role.
Investigation of sulfur release in ETV-ICP-AES and its application for the determination of sulfates by Antje Mroczek; Gerhard Werner; R. Wennrich; Werner Schrön (pp. 34-42).
Electrothermal vaporization inductively coupled plasma atomic emission spectrometry was applied to the determination of sulfur species in aqueous solutions. The sensitivity for sulfur as sulfate was found to be depending on the cations in the sample. For understanding this phenomenon the thermal behavior of sulfuric acid, ammonium sulfate and the sulfates of sodium, zinc, magnesium and silver was studied. There were significant differences in the thermal release of sulfur from these sulfates. To explain these phenomena different reaction mechanisms were calculated using thermodynamic data. Pd(NO3)2 and Ge in KOH were successfully applied as modifiers for the stabilization of the sulfates during the thermal pre-treatment step and to establish a uniform thermal behavior of different sulfates. The stabilization of sulfur using Ge and Pd as modifiers is based on the reduction of the sulfates in presence of carbon, resulting in the formation of GeS and PdS, respectively. This explanation has been supported by comparing the experimental results with thermodynamic calculations considering different reactions for the thermal decomposition of the sulfates. Applying Ge (in KOH) as modifier the absolute detection limit was 300 pg sulfur (e.g. LOD 30 ng mL–1). The significant influence of phosphates on the determination of sulfur could be essentially reduced by Pd as modifier.
The effect of palladium modifier on the efficiency of antimony hydride trapping in graphite furnace atomic absorption spectrometry (AAS) by Sławomir Garboś; Ewa Bulska; Adam Hulanicki (pp. 43-46).
The performance of palladium as permanent chemical modifier electroplated on the surface of a graphite tube for the preconcentration of antimony hydride was examined and compared with thermally formed Pd-coatings. The application of Pd-electroplated tubes allows to perform at least 75 determination cycles without any significant change in the efficiency of hydride collection. This is an advantage over the thermally formed palladium coating which must be obtained individually before each measurement. After the optimization of the system parameters a concentration detection limit of 48 ng/L and an absolute detection limit of 71 pg for a 1.48 mL sample were obtained. The procedure was applied to the determination of antimony at a concentration level of 0.2 μg/L in a tap water sample.
Use of GC and equilibrium calculations of CO2 saturation index to indicate whether freshwater bodies in north-eastern Germany are net sources or sinks for atmospheric CO2 by J. Gelbrecht; Martin Fait; Maria Dittrich; Christian Steinberg (pp. 47-53).
The determination of CO2 saturation by two different methods is described for freshwater bodies of differing trophic states, hydrology and chemistry in the North-East of Germany. Direct measurements were carried out by gas chromatography and values were calculated from the dissolved inorganic carbon concentration and pH. These results were in good agreement. In both cases, the CO2 saturation index was calculated from the carbon dioxide/carbonate/hydrogencarbonate equilibrium in water. An overestimation of CO2 saturation index will be caused at pH > 7 by neglecting the calcium forming ion pairs with HCO3– and CO32–. The CO2 saturation patterns exhibited seasonal changes in all the lakes investigated which were variable within each trophic group. A direct relationship was found between the increasing trophic state and undersaturation of CO2 during the periods of high primary production. Thus, with respect to the atmosphere, these freshwater bodies act mostly as sources of CO2. Periods of ice covering and clear-water phases are characterized by high CO2 supersaturation and therefore the surface waters investigated are CO2 sources for short periods only.
Mass spectrometric identification of polychlorinated dibenzothiophenes (PCDBTs) in surface sediments of the River Elbe by E. Claus; P. Heininger; M. Bade; H. Jürling; M. Raab (pp. 54-58).
HRGC/MS was applied to six sediment samples from River Elbe for the determination of polychlorinated dibenzothiophenes (PCDBTs). Among the studied tri-, tetra- and octa-chlorinated isomers, trichlorinated species were found to be the dominating ones. The estimated concentration levels of the compounds were in the range of approximately 0.02–2 μg/kg dry weight for trichlorinated and 0.1–0.3 μg/kg for octachlorinated species. Tetrachlorinated dibenzothiophenes could not be detected.
Investigations of ground-based clouds at the Mt. Brocken by K. Acker; D. Möller; W. Wieprecht; D. Kalaß; R. Auel (pp. 59-64).
Results of the 1996 field season (April-November) of the cloud chemistry program starting in 1992 at the Mt. Brocken are presented. The mountain site (1142 m a.s.l.) is located in the Harz Mountains/Germany. For a large part of the database (about 40%), both cloud water and drizzle and/or precipitation were present at the same time. A separation into two groups was done: non-precipitating clouds and mixed category of events. More than 2000 one hour samples were collected and analysed for major ions. The mean cloud water pH for the frostfree period in 1996 was 3.9. Histograms giving the distribution of pH values show that the pH values of samples from non-precipitating clouds ranges from 2.5 up to values > 8 and that the distribution is bimodale. For the 1996 field season period as a whole, pH values of cloud water were lower than those of mixed samples (cloud water, drizzle, precipitation) at the Brocken site. This was related to higher concentrations of all ions in cloud water. Cloud base measurements using a ceilometer confirmed the correlation between liquid water content and height above cloud base and consequently the influence of sampling height relative to the cloud base on the total ionic content of cloud water.
Voltammetric determination of heavy metals leached from ceramics by Jerzy Golimowski; Beata Krasnodębska-Ostręga (pp. 65-68).
Anodic stripping voltammetry using a mercury film electrode (MFE) and hanging mercury drop electrode (HMDE) was applied for the determination of trace amounts of lead, cadmium, zinc and copper leached from plates by 4% acetic acid standard solution. The use of a MFE, the fast scan rate (1000 mV/s) by DC voltammetry with subtraction of background current allowed to determine low concentrations of heavy metals. The amounts of metals leached from ware were Pb: 0.1 to 25, Cd: 0.015 to 0.44, Zn: 0.07 to 1.06, Cu: 0.14 to 0.40 μg/mL, depending on the kind of plate and manufacture. Determinations of copper and zinc were carried out using the HMDE electrode in the leachate, determination of tin after medium exchange, and thallium after complexing of lead by EDTA. A significant decrease of metals leached during the second leaching and after washing with detergent solution was found for plates with overglaze decoration.