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Analytical and Bioanalytical Chemistry (v.357, #7)
Improvement of SIMS image classification by means of wavelet de-noising by M. Wolkenstein; H. Hutter; S. G. Nikolov; M. Grasserbauer (pp. 783-788).
Classification is a powerful tool for the extraction of chemical information from analytical images. However, classification may sometimes not be applicable, when the clusters corresponding to single phases overlap due to high noise levels, such that they are not significantly distinguishable. We investigate the effect of the wavelet shrinkage de-noising algorithm on the subsequent classification of analytical images. By application of wavelet de-noising the distinction of phases in classification can be significantly improved.
Improved estimation of the limit of detection in multivariate calibration by K. Faber; B. R. Kowalski (pp. 789-795).
The limit of detection is one of the most important performance characteristics of an analytical procedure. This paper critically examines a recently introduced expression for estimating a multivariate limit of detection. The main result is that the proposed expression is inconsistent. An application from inductively coupled plasma – optical emission spectrometry (ICP-OES) shows that the true limit of detection may be overestimated by more than 20%. In addition, the practical evaluation of the proposed expression amounts to an iterative procedure, which is unattractive from an application point of view. A modification is derived that solves both problems. The relevant expressions are discussed with respect to their interpretability in terms of experimental design.
Salt doping in electronprobe microanalysis by F. A. Guimelfarb; Mikhail N. Filippov; Elena V. Kletskina (pp. 796-800).
A new method of electronprobe microanalysis (EPMA) is suggested. It is based on creating ionic conductivity in frozen water solutions and in polymer films by doping them with a salt. This procedure is effective to prevent surface charging and allows imaging of nonconducting samples by scanning electron microscopy (SEM) as well as X-ray microanalysis. Specifically, this procedure makes it possible to perform EPMA of samples with xerogel matrices, which were used for molecular laser microprobe mass spectrometry analysis, and consequently to provide complex microprobe examination of samples.
Critical evaluation of adsorption-based sampling of vaporized metal species in flue gases by Tiina Harju; Timo Laitinen; M. Pärkkä; Hannu Revitzer; Inkeri Yliruokanen (pp. 801-805).
Diffusion-controlled sampling techniques, i.e. diffusion screens and diffusion tubes (= denuders), can be used in the collection of several vaporized heavy metal species in clean gases (pure N2 atmosphere) at elevated temperatures. Collection efficiencies obtained for Hg, HgCl2, Cd, CdCl2 and ZnCl2 were over 90% using adsorption on Au-coated diffusion screens and Ag-coated denuders. However, the collection efficiencies for Zn and PbCl2 were significantly lower. In field measurements performed at a hazardous waste incineration plant and in a power plant equipped with a circulating fluidized-bed boiler, collection efficiencies seemed to vary noticeably depending on the sampling conditions and metal species to be sampled. Best collection efficiencies were obtained for mercury with both Ag coated denuders and Au coated screens whereas cadmium showed significantly poorer results in field measurements than in the laboratory. Sampling of zinc and lead species seemed to be problematic in all cases. Of the two sampling techniques, the denuder technique is more recommendable than the screen technique for sampling in relatively clean gases. However, neither of these techniques should be used in flue gases without further understanding of the collection mechanisms.
Method for avoiding the interference of formamide with the Karl Fischer titration by Kornelia Schmitt; H.-D. Isengard (pp. 806-811).
The Karl Fischer titration is based on a specific chemical reaction. Several measures exist to make all the water of insoluble samples accessible for the chemical reactants. The most efficient are the titration at elevated temperatures, the use of a homogenizer in the titration vessel and the modification of the polarity of the working medium (essentially methanol) by the addition of appropriate solvents like chloroform or formamide. It is known however that formamide interferes with the Karl Fischer reaction and so causes more or less false results. This effect increases with higher temperatures. A method is therefore presented to avoid this interference, even when working at the boiling point of the working medium. It takes advantage of the fact that the side reaction has a practically constant velocity, at least as long as usual titrations last. Thus, a constant additional consumption of Karl Fischer reagent is observed. This can be accounted for by measuring this effect before the start of the determination and by deducting the additional reagent consumption, which is proportional to the duration of the titration, from the totally added volume. With certain modern titrators this can even be carried out automatically. They can continuously measure the so-called drift, the titration rate necessary to keep the titration cell dry, and have the capability to use this drift as stop criterion for the titration. This means that the analysis is terminated when the drift existing before the titration is reached again. The additional consumption of reagent, to be deducted from the total volume, can (automatically) be calculated from the drift rate and the titration time. The proposed procedure allows the use of formamide as additional solvent, even at high temperatures, in order to shorten determination times considerably. It avoids false results due to the interference, which has so far prevented its use when exact results were desired and when the duration of the analysis was long.
Structure and properties of porous composite membranes of regenerated silk fibroin and poly(vinyl alcohol) and biosensing of glucose via Meldola blue dispersed in polyester ionomer as an electron transfer mediator by H. Liu; Huihong Deng; Kang Sun; Deyao Qi; Jiaqi Deng; Yongcheng Liu; Tongyin Yu (pp. 812-816).
Porous composite membranes of regenerated silk fibroin and poly(vinyl alcohol) were prepared by adding polyethyleneglycol to the composite solution to reduce the mass-transfer resistance to the diffusion of substrate material transport; their surfaces were visualized with scanning electron microscopy. An amperometric glucose biosensor employing Meldola blue dispersed in polyester ionomer as electron transfer mediator was prepared to test the feasibility and workability of the composite membrane as immobilization matrix for glucose oxidase. The cationic exchange property of the polyester ionomer was employed to provide high local concentrations of Meldola blue (MB+) in the polymer film via ion exchange. Performance and characteristics of the glucose biosensor were evaluated with respect to response time, detection limit, applied potential, thickness of polyester ionomer membrane, pH and temperature. The glucose biosensor possesses a variety of advantages including easy maintenance of enzyme, simplicity of construction, fast response time and high stability.
Comparison of sample digestion procedures for the determination of arsenic in certified marine samples using the FI-HG-AAS-technique by G. Damkröger; M. Grote; E. Janßen (pp. 817-821).
High-pressure digestion and a closed-vessel microwave heated system, both employing a mixture of nitric acid and hydrogen peroxide as digesting agent, were tested for decomposing the certified samples of BCR 278 mussel tissue (Mytilus edulis) and of BCR 422 cod muscle to determine arsenic by use of FI-HG-AAS. While the microwave system is insufficient to mineralize arsenic in marine samples (arsenic recoveries of 13±10% in BCR 278, 2±1% in BCR 422; n=4), high-pressure ashing at 300 °C results in recovery percentages of 56±15% (n=4) in mussel tissue (BCR 278) and of 25±10% (n=4) in cod muscle (BCR 422). A dry ashing procedure is given as a reference digestion, yielding complete recoveries of arsenic for both materials. The nitrite interference arising during measurement can be entirely overcome by using an amino sulfuric acid concentration of about 350 mmol/L in the solutions for measurement.
Semi-automatic determination of tin in marine materials by continuous flow hydride generation inductively coupled plasma atomic emission spectrometry by Yong-Lai Feng; H. Narasaki; Hong-Yuan Chen; Li-Ching Tian (pp. 822-826).
A semi-automated continuous flow hydride generation system with inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for the determination of tin in marine materials. The effects of acids (H2SO4 and HCl) were studied. The analytical parameters were thoroughly investigated. Under optimized conditions, the detection limit is 0.4 ng/ml. Interferences from transition elements were investigated and seven masking reagents were tested. L-cysteine hydrochloride monohydrate (1%) was used to mask the interferences from foreign ions. Finally, the accuracy, checked with a marine standard reference material obtained from the National Research Council (NRC), was within the certified value.
Flow injection atomic absorption spectrometery for the standardization of arsenic, lead and mercury in environmental and biological standard reference materials by Gautam Samanta; D. Chakraborti (pp. 827-832).
Results of a thorough study and application of flow injection atomic absorption spectrometry for the determination of As, Pb and Hg in parts per million to sub-parts per billion levels in environmental and biological samples have been described. Various standard reference materials from the National Bureau of Standards, USA, the National Institute of Standards and Technology, USA, the Community Bureau of Reference, Brussels, Belgium and the National Institute for Environmental Studies, Japan and Standard Chinese river sediment were used. By flow injection hydride generation AAS the standard reference materials were analyzed for As and Pb. Mercury was determined by cold vapour flow injection AAS from environmental and biological standard reference materials. The technique is fast, simple and highly sensitive. It takes only 30 s for each analysis from the digested solution. The detection limits of As, Pb and Hg are 1.8 μg L–1 and 2.0 μg L–1 and 1.5 μg L–1, respectively. The results show good agreement with the certified values.
Collaborative study for the quality control of trace element determinations in paint coatings Part 1. Interlaboratory study by K. G. Darrall; A. Pindar; P. Quevauviller (pp. 833-836).
Since the adoption of the European Standard EN71: Part 3 on toy safety, there has been dissatisfaction with the poor reproducibility obtained between laboratories using the test method for the determination of the migration of certain elements from paints to toys. This lack of quality control could result in toys being judged unacceptable with regard to the requirements of the EC Directive 88/378/EEC, which creates a potential barrier to trade. In order to improve the methods of measurements and testing, the Standards, Measurements and Testing Programme (SM&T) is currently supporting a project of which the final aim is to produce paint reference materials. The first step of this collaborative project is aimed to assess and possibly improve the state-of-the-art of trace element determinations in paint coatings through an interlaboratory study, the results of which are presented in this paper.
Evaluation of on-line coupling size exclusion chromatography electrothermal atomic absorption spectrometry for selenium speciation by Francisco Laborda; María V. Vicente; José M. Mir; J. R. Castillo (pp. 837-843).
Chromatographic effluents were on-line analyzed by Zeeman-ETAAS, using a flow-through cell placed in a graphite furnace autosampler as interface. To obtain high sampling rates, the use of fast graphite furnace programmes was studied. Conventional programmes of 96 s were reduced to 18 s by using hot injection (120 °C) and reducing the charring step to 2 s. The increase of the injection volume from 20 to 60 μl lengthened the programme to 46 s. Nickel had to be added to get a comparable response for both inorganic and organic selenium species (selenite and selenomethionine) and to reduce the interferent effect produced in presence of the chromatographic eluent (TRIS 0.01 mol l-1, NH4NO3 0.1 mol l-1, pH 7). The optimized conditions were applied to the speciation of selenium in human erythrocyte lysates by size exclusion LC-ETAAS. Using a high performance size exclusion column selenium could be assigned to proteins of 100 and 35 kDa. Detection limits in the range of 1 ng (2 μg l-1 for 500 μl injection volume) were obtained for the combined technique.
Anionic cartridge preconcentrators for inorganic arsenic, monomethylarsonate and dimethylarsinate determination by on-line HPLC-HG-AAS by M. Gómez; C. Cámara; M. A. Palacios; A. López-Gonzálvez (pp. 844-849).
Preconcentration anionic cartridges in combination with hyphenated FI-HG-AAS and HPLC-HG-AAS have been evaluated for the preconcentration and quantification of total toxic arsenic and of inorganic arsenic, monomethylarsonate and dimethylarsinate species, respectively. Optimum retention and elution parameters of the species on the anionic cartridges are evaluated and the quality parameters of the analysis are reported. The detection limits for the arsenic species under study range from 0.1 μg L-1 to 0.6 μg L-1. The proposed method was successfully applied to the determination of arsenic species in spiked fresh water.
Selenium determination by HG-ICPAES: Elimination of iron interferences by means of an ion-exchange resin in a continuous flow system by L. D. Martinez; M. Baucells; E. Pelfort; M. Roura; R. Olsina (pp. 850-852).
An accurate procedure for the elimination of iron interferences in the determination of selenium in geological materials by the Hydride Generation – Inductively Coupled Plasma Atomic Emission Spectrometry technique (HG-ICPAES) is proposed. A selective removal of iron is achieved by on-line incorporation of a microcolumn filled with strongly acidic cation exchange resin (Dowex 50W-X8). The microcolumn manifold used was interfaced with the hydride generation manifold by a flow injection sample injection valve. After the removal of the iron, a 500 μl sample was injected into a carrier stream of water. This was merged with hydrochloric acid and sodium tetrahydroborate in order to generate the corresponding selenium hydride. The system was found to have a limit of detection of 0.4 ng ml-1 and a relative standard deviation of 2% for 20 ng ml-1 selenium. The application of the method on different Geochemical Standard Reference Samples demonstrated that results were statistically indistinguishable from certified values.
Length-of-stain indicator tubes for the determination of metals in water and solutions by E. I. Morosanova; N. M. Kuz’min; Y. A. Zolotov (pp. 853-859).
Indicator tubes have been proposed for the determination of heavy metals in solutions. Preparation procedures for indicator powders based on noncovalent modifications of reversed-phased silica gel sorbents by analytical reagents have been developed. The effects of pH of the sample, the capacity of the sorbent on the reagent, the flow rate, and the diameter of an indicator tube on the length of the colored zone have been studied. Procedures for the determination of Co(II), Fe(II, III), Cu(II), Cd, and the total content of heavy metals in water and solutions have been elaborated. The procedures have been used to analyze natural and waste waters, soil extracts, and industrial solutions.
Flow analysis preconcentration of Mg and Zn using emulsions for flame atomic absorption spectrometry by T. Yokoyama; Takashi Watarai; Takeo Uehara; Koh-ichi Mizuoka; Kenji Kohara; Masato Kido; Michio Zenki (pp. 860-863).
A preconcentration method combining Water/ Oil/Water (W/O/W) emulsions with flow injection manifolds has been developed for determinations of Mg and Zn. The system consists of a mixing coil filled with Span 80 as a surfactant, palmitic acid or di(2-ethylhexyl) phosphate as an extractant, kerosene as a solvent in the oil phase, and HCl in the inner aqueous phase to form W/O emulsions, an extraction coil for the sample solution to form W/O/W emulsions, a phase separator to waste the outer aqueous phase, a dry bath to demulsify W/O emulsions with 2-ethylhexanol, a phase separator to waste the oil phase, and an air pump to deliver the concentrated sample solution to the flame atomic absorption spectrophotometer. This method proved to be excellent regarding the reproducibility, the rapidity, and the small quantity of sample, compared with the W/O/W emulsions method without the flow injection manifolds. The signal of flame atomic absorption spectrometry (FAAS) after preconcentration of Mg by this method was 2.4 times as large as that before preconcentration. Also, this method suppressed some interferences. The system was applied to FAAS determinations of Mg and Zn in duralumin alloys and Zn in commercial reagents.
Determination of Fe-55 and Ni-63 using semi-preparative ion chromatography – a feasibility study by H. Geckeis; D. Hentschel; D. Jensen; A. Görtzen; N. Kerner (pp. 864-869).
The feasibility of semi-preparative high-performance ion chromatography (HPIC) for the analysis of the activation products Fe-55 and Ni-63 in samples of different sources was studied. A mixed anion/cation exchanger column was applied to the separation of Fe(III), Ni(II) and Co(II) using 1 mmol/L PDCA-solution as an eluent. After fractionation of the eluate, Fe(III)- and Ni(II)-fractions were analysed by low-level liquid scintillation counting (LSC). The method was applied to the analysis of corrosion products originating from the primary circuit of a shut-down nuclear power plant. The limits of detection are dependent on the loading of metal ions on the column and are therefore given in terms of specific activities. For a typical sample composition they were found to be 0.011 Bq per mg Fe for Fe-55 and 0.054 Bq per mg Ni for Ni-63. An assessment of semi-preparative HPIC connected to off-line and on-line LSC as compared with standard radiochemical procedures is given.
Rapid kinetic determination of silver (I), using in-cuvette mixing and computerized data acquisition by A. Safavi; B. Haghighi (pp. 870-873).
The determination of silver(I) based on its catalytic effect on the oxidation of indigo carmine with hexacyanoferrate(III) is described. The reaction is monitored spectrophotometrically by means of a home-made rapid system with computer data acquisition. The decrease in absorbance of indigo carmine at 612 nm, pH 6 and at a fixed concentration of hexacyanoferrate(III) and indigo carmine is proportional to the concentration of Ag(I). The acquired data based on the initial rate and fixed time are processed. Up to 100.0 μg/ml of silver are determined. The limit of detection and average relative standard deviation are 0.13 μg/ml and 1.9%, respectively. The effect of foreign ions on the determination of silver is also discussed. The proposed method is applied to the determination of Ag(I) in expired photographic film.
Determination of palladium by adsorptive stripping voltammetry by Marija Georgieva; B. Pihlar (pp. 874-880).
Adsorptive accumulation of the Pd(II) complex with dimethylglyoxime was evaluated for stripping voltammetry with respect to different parameters. The sensitivity of the method and the linearity between the peak current and the concentration of Pd(II) depends on the ionic strength, the electrode area, the preconcentration time, the transport rate to the electrode, and the potential scan rate. The most appropriate medium was 0.1 mol/L acetate buffer between pH 3.5 and 4. Using 2 min of preconcentration at a 2.6 mm2 electrode and the differential pulse mode, a detection limit of 0.05 μg/L Pd was achieved for liquid samples and 50 ng/g for solid samples. Different aqueous and solid samples were analysed and the recovery from biological and inorganic materials investigated.
Determination of trace elements in AR grade alkali salts after preconcentration by column solid-phase extraction on TiO2 (anatase) by E. Vassileva; K. Hadjiivanov (pp. 881-885).
Column solid-phase extraction using TiO2 (anatase) as a solid sorbent was applied to preconcentrate traces of Cd, Co, Cu, Fe, Mn, Ni and Pb from AR grade alkali salts prior to their measurements by atomic absorption spectrometry (AAS). Multi-element preconcentration was achieved from NaCl, KCl, KNO3, NaNO3, CH3COONa, NaHCO3 and Na2CO3 solutions, whereas the sorption of trace elements from phosphates and sulfates is not quantitative. Optimal conditions (recoveries of the analytes >95%) for solid-phase co-extraction of the most common heavy metal ions are proposed. The conditions for quantitative and reproducible elution and subsequent AAS are established. A method of determination of trace elements in different salts is proposed. It is characterized by precision, reproducibility and a high preconcentration factor. The solid-phase extraction by TiO2, combined with ETAAS allows the determination of 0.1 ng g-1 Cd, 2 ng g-1 Co, 1 ng g-1 Cu and Ni, 0.5 ng g-1 Mn and 0.4 ng g-1 Pb.
In-situ fracture investigations of MgLi-carbon fibre composite materials by AES and data analysis by means of factor and cluster analysis by A. John; Stefan Baunack; Stanislav Kúdela; Klaus Wetzig (pp. 886-893).
Uncoated and 300 nm pyrocarbon coated polyacrylonitril (PAN) based T300 type carbon fibres were pressure infiltrated with molten Mg8Li and Mg12Li alloys at 903 K and 963 K, respectively, and at contact times of 4 s and 30 s. The fracture surfaces were characterized by in-situ Auger electron spectroscopy (AES) to investigate the reason for differences in mechanical properties, which were obtained by tensile strength experiments. Pressure increase occurred during the fracture of all the MgLi samples under ultra high vacuum conditions in the analyzer chamber of the AES apparatus, indicating porosity probably due to poor wetting of the fibres during the infiltration process. As visible in the scanning electron micrographs, the pyrocarbon coated carbon fibres were less attacked by the molten MgLi than the uncoated fibres. The damage seemed to increase, the higher the Li contents, the higher the contact time and the higher the temperature were chosen, whereas pyrocarbon coating may retard this affection. Characteristic objects of the sample fracture surfaces (fibre fracture surface, fibre jacket surface, fibre impression surface and matrix) were investigated by laterally high resolution Auger electron spectroscopy. Oxygen was found to be distributed all over the fracture surfaces of the as-fractured samples, and Mg/Li were identified in a chemically bound form. On all the characteristic objects carbide (Li2C2) formation has been detected. Factor analysis was performed to exctract the principal components from the whole set of differentiated Auger electron spectra in the Mg/Li, C and O spectral regions, respectively. Cluster analysis of the weighting factors (the factor loadings) of the most important principal components lead to a separation of the data set into two main groups due to the presence or absence of a strong carbide C (KVV) peak as result of Ar+ sputter removal of the covering oxide layer; no separation of the objects concerning the reaction conditions was found.
HPLC determination of collectors used for the flotation of heavy metal minerals by Chunshan Zhou; Xingan Xiong; Mingjian Wu; G. Schwedt (pp. 894-896).
A reversed-phase HPLC-method for the separation of mixtures of collectors for the flotation of heavy metal minerals is described. It is based on a Nucleosil 5C18 column, isocratic elution and UV-detection at 238 nm. The mobile phase is methanol-water-5% phosphoric acid (40:60:4, v/v). The method is applied to the determination of six collectors in aqueous solutions from flotation processes. The relative standard deviations are 1.6–3.2% in the concentration range 2–10 mg/L. The detection limits are 1 μg/L for 8-hydroxyquinoline, dimethylglyoxime and salicylic acid, 2 μg/L for salicylhydroxamic acid and 5 μg/L for benzenetriazol and salicylaldoxime, respectively.
Identification of some complexes of humic-like model complexants and metal-loaded sorbents in thin-layer chromatography by S. Iskric; B. Kojic-Prodic; B. Spoljar; R. Kiralj; O. Hadzija (pp. 897-900).
The complexes formed between Cu(II), Pb(II), Cd(II), Zn(II) and Hg(II) salts and some aromatic humic-like complexants in the chromatographic process, simulating natural conditions, were investigated by X-ray powder diffraction and IR-spectroscopic analyses; most of the complexes formed were identified.
Flow injection determination of anionic polyelectrolytes using an anionic surfactant-selective plasticized poly(vinyl chloride) membrane electrode detector by Takashi Masadome; T. Imato; Satoshi Itoh; Yasukazu Asano (pp. 901-903).
A potentiometric flow injection method for the determination of anionic polyelectrolytes utilizing a flow-through type surfactant-selective electrode detector is described. The method is based on the detection of the concentration increase of anionic surfactant liberated from a reagent stream containing an ion associate between cationic polyelectrolyte, poly(diallyldimethylammonium chloride) and anionic surfactant, dodecylbenzenesulfonate, which is caused by the formation of a polyion complex between cationic and anionic polyelectrolytes. The response of the electrode detector as a peak-shaped signal was obtained for injected anionic polyelectrolyte samples. A linear relationship was found to exist between peak height and the logarithmic concentration of potassium poly (vinyl sulfate) (PVSK) with a slope of 30 mV decade-1 in a concentration range of 1.0×10-4 to 1.0×10-3 mol/L. Identical relationships were obtained for sodium alginate and carageenan (also anionic polyelectrolytes) as for PVSK but with a lower sensitivity. The detection limit for PVSK was 2.5×10-5 mol/L. The relative standard deviation for 5 injections of a 2.5×10-4 mol/L PVSK solution was 1.3% and the sampling rate was ca. 10 samples h-1.
Separation and enrichment of traces of explosives and their by-products from water by multiple micro liquid extraction for their determination by capillary gas chromatography by T. Welsch; Holger Block (pp. 904-908).
A fast sample preparation method for the trace determination of some exploxives, by-products and degradation compounds in water by capillary gas chromatography is described. It is based on multiple extractions of the water sample with sub-milliliter amounts of solvent and subsequent concentration of the unified extracts by reducing its volume to a few microliters according to Dünges. The most suitable solvent was methyl-tert.-butylether. With electron caption detection and an aqueous sample volume of 25 to 100 ml, the determination level is in the pg/ml range.
Derivatization of aromatic amines for analysis in ammunition wastewater I. Derivatization via bromination of the aromatic ring by T. C. Schmidt; R. Haas; K. Steinbach; E. von Löw (pp. 909-914).
A new derivatization method for aromatic amines is presented based on the bromination of the aromatic ring system in an acetic acid medium to yield bromo derivatives. The derivatization method is very simple to perform and overcomes several problems common in the analysis of polar aromatic amines. The derivatives are easy to extract with pentane and can be separated with gas chromatography. Due to the introduction of the electron withdrawing bromo substituents sensitive detection using an electron capture detector is possible. The method was used to investigate the contents of amino- and aminonitrotoluenes in water samples from the site of a former ammunition plant.
Microdetermination of proteins by resonance light scattering spectroscopy with tetraiodo phenol sulfonaphthalein by Chun Qi Ma; Ke An Li; Shen Yang Tong (pp. 915-920).
The reaction of tetraiodo phenol sulfonaphthalein (TIPSP) with proteins results in an enhanced resonance light scattering (RLS) at 334 nm. This is the foundation of a new quantitative determination method for proteins in aqueous solution. The assay is characterized by high sensitivity (0.34–12.24 μg/ml), short reaction time (<2 min) and simplicity (one-step assay). The protein-to-protein variability of the method was investigated, which had some relationships with the isoelectric points of the proteins. There is little or no interference from amino acids, from most metal ions and from complexing agents (e.g. EDTA). Interference by some metal ions, detergents and salts can be minimized by dilution. Human serum samples were measured by this method and the results were compared with a traditional method.
Study of the alkylation behaviors of antitumor agents to DNA using a quartz crystal resonator in PEG-DNA solution by Zhao-Hui Lin; Guo-Li Shen; Ye Lin; Ru-Qin Yu (pp. 921-926).
The alkylation of DNA by antitumor agents such as mechlorethamine hydrochloride (mustargen), thiophosphoramide (TSPA), mitomycin c (MMC), bleomycin-A5 and dacarbazine (DTIC) can be detected with quartz crystal resonators (QCR). In the course of alkylation, the resonator frequency change in polyethylene glycol (PEG)-DNA solutions follows the cross-linking of DNA and the cleavage of the sugarphosphate backbone of DNA. It is at least partly attributed to the viscosity change of the PEG-DNA solution and possibly to some extent to the change of mass adsorbed on the QCR surface due to cross-linking and cleavage. Experimental results are consistent with that expected from theory.
Immunosorbents: A new tool for pesticide sample handling in environmental analysis by A. Marti´n-Esteban; P. Fernández; C. Cámara (pp. 927-933).
Immunoaffinity techniques have been widely used for the determination of different analytes in the medical field. However the use of antibodies immobilized in an appropriate support material to preconcentrate pesticides from environmental samples is only recent. The production of antibodies, election of supports, antibody immobilization procedures, elution of analytes from immunosorbents and the more recent applications in the field of pesticide analysis are reviewed. The present review concludes that immunosorbents have great potential and discusses the present limitations and expected future trends.
Trace element contents in atmospheric suspended particles: inferences from instrumental neutron activation analysis by X. Querol; A. Alastuey; A. López-Soler; A. Boix; T. Sanfeliu; V. V. Martynov; P. I. Piven; L. P. Kabina; P. A. Souschov (pp. 934-940).
This study focuses on the determination of trace element concentrations in total suspended particles by instrumental neutron activation analysis (INAA) in two different areas in Northeastern Spain (a rural area influenced by the emissions of a large coal-fired power station, and the urban and industrial areas of Castellón). Total suspended particles were sampled by means of standard MCV high- and medium-volume captors, using cellulose membrane filters of 0.8 and 0.45 μm pore size. Preliminary research was performed on the homogeneous distribution of elements in the sample filters and on the study of blank filters for the calculations of the background average element contents. The results obtained allowed to distinguish different major anthropogenic sources of trace elements in the atmosphere at the sampling sites: a) Zr, Hf, Sc, U and Th are related to atmospheric pollution derived from the ceramic industry of the Castellón area; b) As, Cr, Cs, Rb, Sb, Se, Zn are related to traffic and other industrial emission in the Castellón area, and As, Cr, Sb and Zn to power generation emissions in the rural area.
Nature of the HCl-soluble sulfate in the sequential extraction for sulfur speciation in soils by Bin Chen; X. Shan; Dong-qing Shen; Shi-fen Mou (pp. 941-945).
Thirty soils collected from different regions of China were used to investigate the nature of HCl-soluble sulfate (HCl-S) and to evaluate the importance of HCl-S for sulfur speciation in soils. The soils were first extracted with NaH2PO4 solution to remove water-soluble and adsorbed sulfate, followed by extraction in 1 mol/l HCl at room temperature, minimizing the hydrolysis of organic sulfur into sulfate. Excellent linear correlations (r = 0.986) were found between the HCl-S and the carbonate contents in these soils, indicating HCl-S was mainly the carbonate-occluded inorganic sulfate in calcareous soils, averaging for 39% of total sulfur. However, the traditionally recognized major form of soil sulfate (water-soluble and adsorbed sulfate) only account for 7.5% of total sulfur. The non-calcareous soils were also found to contain some of HCl-S (6.9% of total sulfur). Large errors will occur in the determination of ester sulfur if HCl-S is not subtracted from the HI-reducible sulfur, especially in calcareous soils and soils containing little organic matter, which was the common practice in sulfur speciation studies. The reasonableness of including HCl-S in the subtraction method to determine ester sulfur was further verified by the good correlations between ester sulfur and organic carbon content in the soils
Segmented-flow analysis: On-line microwave sample processing for the analysis of natural waters by I. M. Maksimova; E. I. Morosanova; N. M. Kuz’min; Y. A. Zolotov (pp. 946-949).
A flow system including an on-line coated capillary column for the determination of traces of metal ions in natural waters is proposed, employing a manifold of flow microwave sample processing. This method eliminates the noise caused by the organic matrix, i.e. humic and fulvic acids. The system was applied to the determination of Pb, Co, Mn(II), and Fe(III) in swamp water. The proposed technique can be useful for routine analysis of natural and waste waters.
Study of the complexation of Cu(II) by fulvic acids extracted from a sewage sludge and its compost by Joaquim C. G. Esteves da Silva; Ade´lio A. S. C. Machado; Marta S. S. D. S. Pinto (pp. 950-957).
The complexation of Cu(II) by two samples of fulvic acids (FA) extracted from the raw sewage sludge (RsFA) of a waste water processing plant and from the composted sludge (CsFA) obtained upon aerobical digestion was studied at pH 6.0. Synchronous molecular fluorescence spectroscopy was used to monitor the association of FA with Cu(II) and a self-modelling mixture analysis method (SIMPLISMA) was used to preprocess the spectral data to calculate the number of components with different quenching profiles as function of the Cu(II) concentration and their spectra. The stability constants and a rough estimation of the binding site concentrations were obtained by a Stern-Volmer analysis, by a non-linear least-square method and by a linear procedure. The analysis of the SyF spectra allowed the identification of two binding sites for both samples. The logarithm of the conditional stability constant corresponding to the 1:1 complex formed between the stronger binding site and Cu(II) is about 4 for both samples.
Enzymatic determination of fenitrothion by cholinesterase and acetylcholinesterase on fluorogenic substrates by A. Navas Díaz; F. García Sánchez; V. Bracho; J. Lovillo; A. Aguilar (pp. 958-961).
The action of the enzymes acetylcholinesterase and cholinesterase on the substrates indoxylacetate and 2-naphthyl acetate was studied kinetically. Both enzymes convert the substrates to highly fluorescent products (3-hydroxy-indole and 2-naphthol, respectively). The kinetic curves present the initial rate as the variation of fluorescence for a unity of time (ΔF/Δt) against the substrate concentration. This enzymatic reaction was investigated in presence of the inhibitor organophosphate pesticide fenitrothion. From the kinetic curves the enzymatic parameters and enzyme and substrate concentrations used for the calibration curve can be obtained. Four simple spectrofluorimetric methods for the enzymatic determination of fenitrothion were developed showing detection limits between 5.5 to 19.5 μmol/l, depending on the enzyme and the substrate used. The precisions (R.S.D.) of the methods were between 1.6 and 9.6%. A comparative study of the kinetic enzymatic parameters and the detection limits was performed. A good correlation was obtained between inhibition constants and the detection limit.
Electrochemical study of the herbicide Tribenuron Determination in commercial samples by Carlos Olmedo; L. Deban; Mariano Coca; Marisol Vega; Francisco de la Rosa (pp. 962-966).
The herbicide Tribenuron has been investigated. It has an acidic character with a pKa value of 4.1. Hydrolysis was confirmed and its rate increased with temperature and acidity, light influence was not observed. Electrochemical characteristics of this compound have been studied at pH values from 1 to 7 by applying DC, TAST and DP polarography as well as cyclic and differential pulse voltammetry at the HMDE. The reduction of Tribenuron occurs in two processes, the first at pH<7 and the second at pH<4. This study is devoted to the first process, which has been demonstrated to be irreversible and simultaneously governed by diffusion and adsorption phenomena. Both hydrolysis and polarographic reduction of Tribenuron yielded the same degradation products: 2-methoxycarbonylbenzenesulfonamide and 2-N-methyl-amino-4-methoxy-6-methyl-1,3,5-triazine. The quantitative determination of Tribenuron can be carried out by DPP with a detection limit of 92 μg/L or by adsorptive stripping voltammetry reaching a detection limit of 2.6 μg/L. Assays of commercial samples are described.
UV-spectrophotometric determination of ketoprofen and paraben in a gel preparation by partial least-squares calibration by M. Blanco; J. Coello; H. Iturriaga; S. Maspoch; S. Alaoui-Ismaili (pp. 967-972).
Partial least-squares calibration was used for the simultaneous UV spectrophotometric determination of the active principle (ketoprofen) and preservative (parabens) in a pharmaceutical preparation commercially available in gel form. Calibration mixtures were prepared by mixing pure solutions of the analytes. The analytes were extracted and the UV spectrum of the resulting dispersion was recorded. Suppression of the effect of undissolved gel components was accomplished by prior centrifugation, using first and second-derivative spectra, introducing artificial baseline changes and adding the turbidity effect on the sample spectrum to some of the spectra in the calibration matrix. Both the second-derivative and the addition of the turbidity effect allow the quantification of non-centrifuged samples, the last one seems to be a little more effective. The results thus obtained are compared with those provided by HPLC following centrifugation of the samples.
PLS-UV spectrophotometric method for the simultaneous determination of paracetamol, acetylsalicylic acid and caffeine in pharmaceutical formulations by Z. Bouhsain; Salvador Garrigues; M. de la Guardia (pp. 973-976).
A simple and fast analytical procedure is proposed for the simultaneous determination of paracetamol, acetylsalicylic acid and caffeine in pharmaceuticals by means the partial least square treatment of the spectrophotometric absorbance data between 216 and 300 nm, taken at 5 nm intervals. The method involves the use of 8 standard mixtures of the three compounds assayed, considered at two concentration levels, and the measurement of the absorbance of samples in a 20% (v/v) ethanol in water solution previously filtered. In the analysis of real and synthetic samples precise and accurate values were obtained by the aforementioned procedure, providing in all cases variation coefficients and accuracy errors lower than 5% which agree with the tolerance level established by the pharmacopoeia for this kind of samples which is ±10%.
Titrimetric and spectrophotometric determination of chlorhexidine digluconate in tooth pastes by R. Borissova; Sirma Mandjukova (pp. 977-980).
New titrimetric and spectrophotometric methods for the fast determination of chlorhexidine digluconate (CHG) are described. The titrimetric determination is based on the precipitation of CHG as a 1 : 1 complex with Cu2+-ions and EDTA back-titration of the non-bonded Cu2+-ions without separating the precipitate. The spectrophotometric determination is based on the formation of a soluble CHG associate with dodecylsulphate (DDS) in a mixed medium of DDS-H2SO4-propanol. Both methods are applied to tooth pastes. When analysing a series of identical samples, the coefficient K (absorption of 1 g of the matrix) could be determined. Standard tooth pastes and corresponding placebo-compositions (containing all components except CHG) were specially prepared for the investigations and for estimating the accuracy of the methods.
Characterization of cocoa butters and other vegetable fats by pyrolysis-mass spectrometry by E. Anklam; Maria Rosa Bassani; Thomas Eiberger; Stefan Kriebel; Markus Lipp; Reinhard Matissek (pp. 981-984).
Pyrolysis Mass Spectrometry (Py-MS) was used for the discrimination of cocoa butters from other vegetable fats. Mass spectra ranging from 50 amu to 250 amu were analyzed by principal component analysis (PCA) and with neural nets. The application of neural nets leads to a good discrimination between the two classes. Detailed analysis of the nets revealed that only the first 60 masses were used within the net. The use of PCA requires a careful selection of the number of masses included in the calculation. Canonical variance analysis was applied to determine the significant masses. Optimal performance of PCA was observed only using the first 22 significant masses. Most of these masses were different from the ones used by the neural net. It seems that the mass spectra obtained by Py-MS contain sufficient information for the discrimination of pure cocoa butter from other vegetable fats, but none of the methods seems to be able to extract all information available. Neural net provides a very robust method for this task and no prior data selection was necessary.
Spectrophotometric micro-method for the determination of ethanol in commercial beverages by Andrea D. Magrí; A. L. Magrí; Fabrizio Balestrieri; Amalia Sacchini; D. Marini (pp. 985-988).
A sensitive spectrophotometric method for the determination of ethanol with potassium dichromate was developed. Chromium(VI), in 7 mol L-1 perchloric acid, reacts quantitatively with ethanol to form chromium(III) and acetic acid. The reaction is complete in about 15 min at room temperature and the chromium(VI) consumed may be determined by the decrease of the absorbance at 267 nm. The analytical working parameters (such as acidity and ionic strength of the solution, temperature and time of the reaction, chromium(VI) concentration, matrix interferences) were optimized. The apparent molar absorptivities of chromium(VI), in the monomer and dimer form, and the equilibrium quotient for the dimerization reaction were determined in 3 mol L-1 perchloric acid solution. The method was applied to the analysis of micro samples of commercial beverages (beers, wines and spirits) without the previous distillation of ethanol.
Adsorptive stripping voltammetry of Tartrazine at the hanging mercury drop electrode in soft drinks by J. J. Berzas Nevado; J. Rodríguez Flores; M. J. Villaseñor Llerena (pp. 989-994).
Adsorptive stripping voltammetry was used for the determination of trace amounts of the dye Tartrazine (E-102) by square-wave (SWS) and differential pulse techniques (DPS). Its adsorptive voltammetric behaviour was investigated at different pH media. NH4Cl/NH3 buffer solution was chosen as the most suitable, taking into account the sensitivity and definition of the reduction peaks obtained. The effects of the experimental parameters on the determination are discussed. Standard deviations of 3.3% and 2.6% were obtained by SWS and DPS for 100 and 50 μg/L Tartrazine solutions, respectively (n = 10). Both methods were applied to determine the dye in several commercial soft drinks, containing very small amounts of it. Measurements were made directly in the commercial samples. A comparison of the results obtained by the proposed voltammetric methods with those of an HPLC method was also made. Good correlations between the voltammetric results and the values supplied by the manufacturer were found, whereas recoveries of the same order of magnitude were obtained by the HPLC method.
Determination of palladium by a new preconcentration method (Mg-W cell)-electrothermal atomic absorption spectrometry by K. Ohta; J. Ogawa; T. Mizuno (pp. 995-997).
A new concentration method for palladium using Mg-W cell-electrodeposition has been developed. The method was combined with electrothermal atomic absorption spectrometry (ETAAS) with a tungsten tube atomizer. The detection limit of palladium by this method was 0.37 ng ml–1 (3 S/N). The severe interferences on the AAS signal of palladium caused by large amounts of Al, Ca, Cu, Fe, K, Na, Pb and Zn were eliminated by the Mg-W cell-electrodeposition method. The method was adapted for the determination of palladium in environmental samples. The recovery of palladium spiked environmental samples was in the range of 102 to 114%.
Flame atomic absorption spectrometry using a microvolume injection technique for the determination of Cu, Zn, Ca, Mg and Fe in whole blood from healthy infant and mother ears by Sufen Shang; Wang Hong (pp. 997-999).
An FAAS method for the determination of Cu, Zn, Ca, Mg and Fe using a microvolume injection technique is described. The injection volume for the determination of each element is 10 μl and the calibration graphs are linear over the ranges 0.05–1.5, 0.1–3.0, 0.1–2.0, 0.1–2.0 and 1.0–6.0 mg/l for Cu, Zn, Ca, Mg and Fe, respectively. The relative standard deviations are 2.6%, 2.8%, 3.0%, 1.3% and 2.5%, the rates of recovery 98%, 100%, 99%, 99% and 97%. The method was successfully applied to the determination of these elements in whole blood from healthy infant and mother (lying-in) ears.
Application of derivative UV spectrophotometry to the simultaneous determination of nitrate and nitrite ions in bath solutions for alkaline black-oxidation of steel by E. Bobrowska-Grzesik; Andrzej M. Grossman (pp. 1000-1001).
Second order derivative spectrophotometry was applied to the determination of nitrite and nitrate ions in bath solutions for alkaline black-oxidation of steel. The measurements were directly taken after dilution of the samples at λ = 336.4 nm for NO3 – and λ = 390 nm for NO2 –. The method was checked on artificial mixtures and applied to real samples containing approximately 5.5% NaNO2 and 6% NaNO3. The results agree well with those obtained by the standard manganometric method.
Spectrophotometric flow injection determination of trace iodide in table salt and laver through the reaction of iodate with 3,5-Br2-PADAP and thiocyanate by Junying Sun; Xingguo Chen; Zhide Hu (pp. 1002-1005).
A new simple, rapid and sensitive spectrophotometric flow injection method for the determination of trace iodide is described based on an ion associate of iodate (IO3 –) with 2- (3,5-dibromo-2-pyridylazo)-5-diethylamino-phenol (3,5-Br2-PADAP) and thiocyanate (SCN–). In a strongly acidic medium, this unstable violet product was formed with an absorption maximum at 605 nm. Flow injection is an ideal method to reproducibly monitor the transient signal. Various parameters were optimized using the Super Modified Controlled Weighted Centroid Simplex Method (SMCWC). Under the optimum experimental conditions, iodide could be determined in the range of 1.00 × 10–6 and 2.4 × 10–5 mol l–1. The correlation coefficient of the calibration curve is 0.9991. With a sampling frequency of 80 h–1, the detection limit for iodide is 5.0 × 10–7 mol l–1. The proposed method has been applied to the determination of trace iodide after oxidizing I– in table salt or laver to IO3 –. In addition, the mechanisms of the ion association reaction was studied.
Spectrophotometric determination of trimethoprim by oxidation in drug formulations by S. Z. Qureshi; M. I. H. Helaleh; N. Rahman; R. M. A. Q. Jamhour (pp. 1005-1007).
A spectrophotometric determination of trimethoprim is described based on the reaction of its amine group with persulfate which acts as a strong oxidizing agent in alkaline media. The reaction produces a stable yellow colored compound after heating in a boiling water bath for 30 min. At λmax 355 nm, Beer’s law is obeyed in the concentration range 10–60 μg ml–1 with a molar absorptivity of 2.7 × 103 l mol–1cm–1. The method is applied to formulations with sulfamethoxazole.
Acid/extraction treatment of bivalves for organotin speciation by J. L. Gomez-Ariza; E. Morales; I. Giraldez; R. Beltran; J. A. Pozas Escobar (pp. 1007-1009).
A method is described for leaching of nanogram amounts of monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), monophenyltin (MPT), diphenyltin (DPT), triphenyltin (TPT), and monomethyltin (MMT) from bivalves. The procedure is based on soaking the samples in a water-hydrogen bromide mixture (1:1) with magnetic stirring for 30 min followed by extraction with a 0.04% (w/v) tropolone solution in dichloromethane for 2 h. Organotins are determined by GC-FPD after clean-up through a Florisil column and fat hydrolysis by 1mol/L NaOH, followed by derivatization through Grignard pentylation. The method has been applied for an investigation of the occurrence of organotins in bivalves in south-west Spain.