Philosophical aspects of chemometrical strategy in Analytical Chemistry

Summary This paper discusses the philosophical aspects of the three main chemometrical strategies in analytical chemistry: statistical data treatment, optimization and modelling, pattern recognition. It is possible by a more general consideration of these approaches to find a proper place of different philosophical categories such as form and content, induction and deduction, concrete and general in analytical chemistry. The philosophical aspect of the considerations allows a deeper penetration into the theoretical basis of chemical analysis.

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Philosophische Betrachtungen zu chemometrischen Strategien in der Analytischen Chemie

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Presented at the First International Symposium on History and Philosophy in Analytical Chemistry, Vienna, November 22–23, 1985     

Analytical speciation as a tool to assess arsenic behaviour in soils polluted by mining

A study is performed to evaluate the occurrence of arsenic in polluted soils using acidic extractions and liquid chromatography–hydride generation–atomic fluorescence spectrometry (LC–HG–AFS) for speciation analysis. Seven soil samples were collected in an abandoned area polluted by mining in the Eastern Pyrenees (Spain), and two uncontaminated soils were taken for reference purposes. Moreover, the total arsenic content is evaluated in two different sieved fractions in order to obtain information on the possible particle-size-dependent association of arsenic with soil components. Soil samples were extracted with both phosphoric and ascorbic acids and the stabilities of the extracted species were studied. The arsenic species were determined by LC–HG–AFS. In addition, the ability of soil grinding to effect species change is also assessed. Arsenite and arsenate were found in the polluted soils, but only arsenate was found in the unpolluted soils. The quality of the results was assessed through a mass balance calculation and by analysing two soil Certified Reference Materials. Valuable information regarding arsenic occurrence in the studied soils is obtained from the speciation results. The presence of arsenite in the extracts can be attributed to arsenopyrite residues, whereas the presence of arsenate indicates release from weathered material. Figure Abandoned mining polluted area in Eastern Pyrenees     

Multivariate statistical assessment of polluted soils

This study deals with the application of several multivariate statistical methods (cluster analysis, principal components analysis, multiple regression on absolute principal components scores) for assessment of soil pollution by heavy metals. The sampling was performed in a heavily polluted region and the chemometric analysis revealed four latent factors, which describe 84.5 % of the total variance of the system, responsible for the data structure. These factors, whose identity was proved also by cluster analysis, were conditionally named “ore specific”, “metal industrial”, “cement industrial”, and “steel production” factors. Further, the contribution of each identified factor to the total pollution of the soil by each metal pollutant in consideration was determined.     

Analytical investigations of tunnel magnetoresistance layers

The basic elements of tunnel magnetoresists are two magnetic layers separated by an insulating barrier layer. The uniformity of this only 1–2 nm thick barrier layer up to dot edges and the chemical composition of the layers are properties important for the efficiency of tunnel magnetoresistance devices. These key-properties have been investigated by analytical TEM methods like high resolution TEM imaging and energy-filtered imaging. With regard to the chemical composition the TEM results have been confirmed by XPS investigations. The subsequent oxidation of the barrier is one of the most critical steps of the deposition procedure of the layer stacks. An undersized oxygen dose leads to an incomplete oxidation of the barrier layer with uncontrollable tunnel behaviour. An overdose of oxygen leads to oxygen diffusion in the layers beneath the barrier and uncontrollable magnetic hardness of the lower magnetic electrode.     

Analytical TEM investigations of high-temperature superconductors

Electron diffraction and energy dispersive X-ray spectroscopy as analytical transmission electron microscopic methods have been applied to Y-Ba-Cu-O superconductors. The evaluation of diffraction patterns by means of the MS-WINDOWS program ELDISCA is demonstrated. The course of X-ray linescan signals in the transition range between YBa₂Cu₃O_7– matrix and Y₂BaCuO₅ inclusions is explained by calculations based on a mathematical model which is described. Errors of quantiative X-ray spectroscopic results and their reasons are shown.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Analytical investigations of phenyl arsenicals in groundwater

Phenylic arsenic compounds are the main contaminants in groundwater at abandoned sites with a history of arsenic containing chemical warfare agents (CWA). A fast and sensitive HPLC-ICP-MS method was developed to determine inorganic arsenic compounds like arsenite and arsenate as well as the degradation products of the arsenic containing warfare agents (phenylarsonic acid, phenylarsine oxide, diphenylarsinic acid). Beside these arsenic species the groundwater samples contained also high iron contents (up to 23 mg/l as Fe(II)) which led to precipitates in the samples after coming into contact with the atmosphere. Preservation immediately after sampling by phosphoric acid has shown that a successful avoidance of any losses of any arsenic species between sampling and analysis was possible. The suggested analytical method was applied to groundwater samples taken from different depths at a polluted site. The main contaminant in the water samples was diphenylarsinic acid (up to 2.1 mg/l) identified by ESI-MS, but also elevated concentrations of inorganic arsenic (up to 240 microg/l) were found.     

Proficiency test on the determination of mineral oil from polluted soils

Mineral oil products are abundant sources of environmental contamination. A Finnishproficiency test was carried out to investigate the quality of data provided in an analysis of mineral oil in polluted soils. The homogeneity and stability of the samples were tested. The calculated concentration or the median value of the results was used as the assigned value because of the unavailability of certified reference materials (CRMs). The samples were analysed using an infrared spectroscopy (IR) or gas chromatography (GC) procedure. Even if the participating laboratories had little experience with GC, the results were promising. Hence, the GC procedure will replace IR as the new ISO standard (ISO/DIS 16703) in the near future in many Finnish environmental laboratories. There is a need for CRMs for the determination of mineral oil using the GC method due to common contamination problems caused by mineral oil. Received: 9 December 2001 Accepted: 14 February 2002     

Three-stage sequential extraction procedure for metal partitioning in polluted soils and sediments

The sequential extraction procedure proposed by the Standard, Measurements and Testing program "SM&T" of the European Union has been applied to evaluate the amounts of Cr, Cu, Mn, Ni, Pb and Zn, extracted at each stage and indirectly their mobility and bioavailability in soil and sediment samples from a polluted area. Analysis of the extracts was carried out by flame atomic absorption spectrometry (FAAS). No significant matrix interferences were found except for Cr in the acetic acid and hydroxylammonium chloride extracts, which required determination by the standard additions method. Both of soils and sediments studied show similar partitioning of Mn, Ni, Cu and Cr. Mn and Ni can be considered to have significant component bound to the acido-soluble fraction, whereas, Cr and Cu occur largely in the organic and residual phases. The partitioning of Pb and Zn was different between soil and sediment. In terms of mobility and bioavailability, in soils, Ni and Mn can be regarded as moderately available followed by a lower availability of Pb while Cu, Zn and Cr have a very limited availability. In sediments, a higher availability (short-medium term) of Mn and Zn was presumed followed by a lower availability of Ni and Pb, whereas, Cu and Cr, occurring largely in the organic and residual phases, were of very limited availability.     

The kinetics of Cd, Pb and Cr extraction from artificially polluted soils

The kinetics of Cd, Pb and Cr extraction with HCl from polluted chernozem and humous alluvial soils was investigated. The efficiency of the extraction was more than 90% for Cd and more than 80% for Pb. In both cases, the extraction reached the equilibrium state. For Cd and Pb, the metal-ion removal processes in the first 4 h of extraction can be modelled by two simultaneous, pseudo-first-order, irreversible reactions. One of the reactions is fast and can be attributed to H⁺–Mⁿ⁺ exchange reaction occurring on the surface of inorganic minerals as well as in the metal–humic acid complexes and to the dissolution of the water-insoluble precipitates.The minor portion of the metal ions took part in a rather slow reaction, where H⁺ ions exchange with metal ions bound in the internal lattice sites. The slow dissolution of the metal compounds should also be considered. The slow extraction partly can be attributed to slow irreversible processes (e.g., diffusion from the internal lattice sites).In the case of Cr(III), the extraction was found to be a very slow process; the efficiency of removal was less than 25%. The system did not attain the equilibrium state. Presumably, the rates of extraction processes are intermediate between those of the slow and fast reactions.     

Speciation of heavy metals in polluted soils by sequential extraction and ICP spectrometry

Heavy metals were leached from various polluted soils by selective extraction reagents (water, BaCl2, acetate buffer + EDTA, HNO3) in order to establish the distribution of the chemical species of Cd, Zn, Cu and Pb. The leachates were directly injected into a plasma spectrometer in order to analyse immediately the extraction solution. This continuous on-line analysis gives qualitative information about the chemical behaviour of each element in function of the type of soil. It permits also to modify the extraction procedure for each sample studied by adjusting the volume of the extraction solution, the time of extraction, or by choosing another extraction reagent more adapted to the sample. The sum of the respective fraction is in rather good agreement with the total analysis of the soil.     

Analytical investigations on cephalosporins--IV: application of Ellman's reagent

The application of 5,5'-dithiobis(2-nitrobenzoic acid) (Ellman's reagent) for the determination of microgram quantities of various selected cephalosporins in aqueous solution is described. Cephalosporin derivatives (cephalothin sodium, cephacetrile sodium, cefamandole lithium and nafate, cefoperazone sodium and ceftizoxime sodium) have to be treated with 0.5N sodium hydroxide before determination with Ellman's reagent, which reacts with free thiol groups. An aliquot of the solution is reacted with Ellman's reagent in pH 7.2 phosphate buffer and the absorbance of the resulting yellow solution is measured at 410 nm. The method, which is simple and precise, has been applied to determination of those cephalosporins in formulations, the results being compared with those obtained by the Ni-hydroxylamine method.     

Analytical investigations on cephalosporins--I: spectrophotometric determination of ceftriaxone

The hydroxylamine-nickel and imidazole-mercury(II) methods for the determination of penicillins and cephalosporins have been adapted to the determination of ceftriaxone both in bulk form and in pharmaceutical formulations.     

Analytical investigations of tree rings by laser ablation ICP-MS

Laser sampling inductively coupled plasma mass spectrometry has been used for the quantitative determination of trace elements to characterize annual growth rings of trees. The elements studied are Mg, Al, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Cd, Ba, Tl, Pb, Bi and U. Cellulose mixed with multielement standard solution pressed into pellets were used for the calibration. Using internal standardization with ¹²C the precision is typically better than 10% relative standard deviation. The limits of detection were limited by the purity of the cellulose. Analytical figures of merit and the analytical results are discussed in terms of environmental analysis.     

Thermogravimetric and differential thermal analytical investigations on sewage farm soils

Soil substrates of sewage farms (inflow of sewage areas) and of closed sewage farms were investigated by means of thermogravimetry and differential thermal analysis. The results were compared with those obtained for control samples from outside the sewage farms.The organic matter of actively used sewage areas (inflow) contains a remarkable amount of easily oxidizable compounds brought to the inflows by suspended matter.Beside these compounds, macromolecular organic substances predominate in the composition of the organic matter and are responsible for an immense heat release in the high temperature range of the thermal studies.In the substrates of closed sewage farm inflows or of other sewage farm areas which do not belong to the inflows, the amounts of volatile and easily oxidizable compounds decrease rapidly. The substrates hardly differ in their reaction temperatures from control samples. The influence of single macromolecules on the exothermic oxidation is reduced with increasing humification.     

Analytical characterization of coated carbon fibres

Summary Carbon fibres must be coated with a barrier layer in their application as reinforcement in metal matrix composites (MMC) to avoid reactions between the matrix and carbon. Materials frequently used are SiC, pyrolytical carbon or these materials in combination. The reactivity between the metallic matrix and the barrier layer depends on the stoichiometry and structure of the barrier material. XPS and AES are suitable methods for the investigation of the surface and of composition of the layer of the coated fibres. Additionally Raman-spectroscopy has been used to aid the distinction between the bonding states of carbon in the barrier layer and the fibre. The problems of the analysis of small, fibre-like materials are discussed.     

Analytical characterization of thin carbon films

CH(x) films on silicon substrates deposited by a Mesh Hollow Cathode Process (MHC) were analyzed by various techniques. The films were produced with varying deposition times, resulting in thicknesses ranging from ~2-20 nm. X-Ray Reflectivity (XRR) was used to determine the film thicknesses and the deposition rate. A good correlation of measured XRR thicknesses with SIMS sputter depths down to the film-substrate transition was found.An AFM-based nanoscratching technique was applied to test the wear resistance of the thin overcoats. The MHC films reveal slightly decreasing scratch resistance for reduced film thicknesses, which can be explained by a higher fraction of soft interface zones for thinner films.This is in accordance with Raman spectroscopic measurements in the visible spectral range which were carried out to examine the carbon bonding properties. Combined analysis of G peak position and D/G peak intensity ratio indicates a more graphitic structure for film thicknesses less than 10 nm.     

Occurrence of methylated arsenic species in parts of plants growing in polluted soils

Arsenic compounds were determined in extracts of branches, leaves and roots from plants growing in a mining contaminated area. The selected species were Dryopteris filix-max, Quercus pubescens, Dipsacus fullonum, Alnus glutinosa, Buxus sempervirens and Brachythecium cf. reflexum. Total arsenic content in the subsamples was analysed by ICPMS after acidic digestion. In general, concentrations in the plant parts followed the gradient roots?>?branches?>?leaves indicating that they are arsenic-resistant plants. Arsenic species were determined in water/methanol (9?+?1, v/v) extracts by HPLC-ICPMS. Different levels of organoarsenicals were found depending on plant part and plant species. Higher percentages of organoarsenic compounds were recorded in branches and leaves (up to 35% in the boxtree sample), than in roots (0.7–5.2% in the same plant species). The absence of organic arsenic species in the soil where the plants were collected and the low levels of organoarsenicals found in the roots, indicate that the studied plants have the ability to accumulate or synthesise organoarsenic compounds in relatively high percentages, and this information contributes to enlarge the knowledge of arsenic uptake and speciation in plants.     

Effect of oxidizing gas pressure on laboratory-scale decontamination of soils polluted by hydrocarbons

Three standard European soils were artificially contaminated with hexachlorobenzene, 4-chlorobiphenyl, and naphthalene. Small piles (ca. 30 mg) of contaminated soil, or neat soil in control runs, were then heated in the crucible of a thermogravimetric analyzer from room temperature to ca. 450°C at 5°C/min. To investigate effects of ambient gas pressure on contaminants removal, soil specimens were subjected to closely similar heating schedules under either 0.1 or 0.01 MPa pressure of air. The lower pressure augmented decontamination, reducing by as much as 20–45°C the temperature necessary for a given extent of pollutant removal, and increasing the maximum rate of decontamination. The precise magnitude and duration of such pressure-induced improvements in decontamination varied with pollutant and soil type. Predictions of a contaminant evaporation-diffusive transport model were in reasonable agreement with experimentally observed pressure trends. Higher diffusion coefficients for pollutant vapor under reduced pressure are believed to be responsible for the observed pressure effects.     

ToF-SIMS characterization of microplastics in soils

Microplastics pollution is becoming one of the most serious threats to the surface ecosystem of the earth; it is widespread in oceans, rivers, sediments, soils, and organisms. It is a growing concern as an environmental pollutant, which currently has no clear detection standard. Detection methods still need to be constantly supplemented and improved. This study explored a novel method called time-of-flight secondary ion mass spectrometry (ToF-SIMS) in this field. Four types of microplastics in farmland soils, namely, polypropylene, polyvinyl chloride, polyethylene terephthalate, and polyamide 6, were successfully identified in terms of particle size and abundance by combining the high molecular specificity with ion imaging capability of ToF-SIMS. The procedure based on ToF-SIMS analysis also provides a methodological reference and basic data for the investigation and research of microplastics in soil, coastal beaches, and sediment.