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Analytical and Bioanalytical Chemistry (v.370, #7)


Molecularly imprinted polymers: new molecular recognition materials for selective solid-phase extraction of organic compounds by A. Martín-Esteban (pp. 795-802).
During the last few years molecularly imprinted polymers have appeared as new selective sorbents for solid-phase extraction of organic compounds in different samples. Molecular imprinting technology involves the preparation of a polymer with specific recognition sites for certain molecules. Once the polymer has been obtained, it can be used in solid-phase extraction protocols, where a careful selection of the most appropriate solvents to be used in the different steps (sample loading, washing and elution) is needed in order to extract the target analyte selectively. This review describes the state of the art of this methodology, including the preparation of imprinted polymers, a process description for molecularly imprinted solid-phase extraction, as well as more recent applications. It is concluded that molecularly imprinted solid-phase extraction is a powerful tool to selectively isolate certain analytes, and future advances are to be expected in order to widen the field of application.

web-based interactive data processing: application to stable isotope metrology by R. M. Verkouteren; J. N. Lee (pp. 803-810).
To address a fundamental need in stable isotope metrology, the National Institute of Standards and Technology (NIST) has established a web-based interactive data-processing system accessible through a common gateway interface (CGI) program on the internet site http://www. nist.gov/widps-co2. This is the first application of a web-based tool that improves the measurement traceability afforded by a series of NIST standard materials. Specifically, this tool promotes the proper usage of isotope reference materials (RMs) and improves the quality of reported data from extensive measurement networks. Through the International Atomic Energy Agency (IAEA), we have defined standard procedures for stable isotope measurement and data-processing, and have determined and applied consistent reference values for selected NIST and IAEA isotope RMs. Measurement data of samples and RMs are entered into specified fields on the web-based form. These data are submitted through the CGI program on a NIST Web server, where appropriate calculations are performed and results returned to the client. Several international laboratories have independently verified the accuracy of the procedures and algorithm for measurements of naturally occurring carbon-13 and oxygen-18 abundances and slightly enriched compositions up to approximately 150% relative to natural abundances. To conserve the use of the NIST RMs, users may determine value assignments for a secondary standard to be used in routine analysis. Users may also wish to validate proprietary algorithms embedded in their laboratory instrumentation, or specify the values of fundamental variables that are usually fixed in reduction algorithms to see the effect on the calculations. The results returned from the web-based tool are limited in quality only by the measurements themselves, and further value may be realized through the normalization function. When combined with stringent measurement protocols, two- to threefold improvements have been realized in the reproducibility of carbon-13 and oxygen-18 determinations across laboratories.

Collaborative study to improve the quality control of trace element determinations in polymers. Part 2. Certification of polyethylene reference materials (CRMs 680 and 681) for As, Br, Cd, Cl, Cr, Hg, Pb, and S content by A. Lamberty; W. Van Borm; P. Quevauviller (pp. 811-818).
Two polymer (polyethylene) reference materials have been produced in support of EC Directive 94/ 62/EC on plastic packaging and packaging material The paper describes the preparation of the materials, the analytical work performed to characterize their homogeneity and stability, and the certification of the materials for a range of elements. The technical and statistical evaluation of the results are also summarized.

Preparation of calibration materials for microanalysis of Ti minerals by direct fusion of synthetic and natural materials: Experience with LA–ICP–MS analysis of some important minor and trace elements in ilmenite and rutile by M. Ødegård; J. Mansfeld; S. H. Dundas (pp. 819-827).
Calibration materials for microanalysis of Ti minerals have been prepared by direct fusion of synthetic and natural materials by resistance heating in high-purity graphite electrodes. Synthetic materials were FeTiO3 and TiO2 reagents doped with minor and trace elements; CRMs for ilmenite, rutile, and a Ti-rich magnetite were used as natural materials. Problems occurred during fusion of Fe2O3-rich materials, because at atmospheric pressure Fe2O3 decomposes into Fe3O4 and O2 at 1462 °C. An alternative fusion technique under pressure was tested, but the resulting materials were characterized by extensive segregation and development of separate phases. Fe2O3-rich materials were therefore fused below this temperature, resulting in a form of sintering, without conversion of the materials into amorphous glasses. The fused materials were studied by optical microscopy and EPMA, and tested as calibration materials by inductively coupled plasma mass spectrometry, equipped with laser ablation for sample introduction (LA–ICP–MS).It was demonstrated that calibration curves based on materials of rutile composition, within normal analytical uncertainty, generally coincide with calibration curves based on materials of ilmenite composition. It is, therefore, concluded that LA–ICP–MS analysis of Ti minerals can with advantage be based exclusively on calibration materials prepared for rutile, thereby avoiding the special fusion problems related to oxide mixtures of ilmenite composition. It is documented that sintered materials were in good overall agreement with homogeneous glass materials, an observation that indicates that in other situations also sintered mineral concentrates might be a useful alternative for instrument calibration, e.g. as alternative to pressed powders.

Development of perfluorocarbon (PFC) primary standards for monitoring of emissions from aluminum production by G. Rhoderick; Pamela Chu; Eric Dolin; Jerry Marks; Touche Howard; Mark Lytle; L. McKenzie; Don Altman (pp. 828-833).
An EPA Voluntary Aluminum Industrial Partnership (VAIP) program has been formed to help US primary producers focus on reducing the emissions of two perfluorocarbons (PFCs), tetrafluoromethane (CF4) and hexafluoroethane (C2F6), during the production of aluminum. To ensure comparability of measurements over space and time, traceability to national sources was desirable. Hence, the EPA approached the NIST to develop a suite of primary standards to cover a mole fraction (concentration) range of 0.1 to 1400 μmol mol–1 for CF4 and 0.01 to 150 μmol mol–1 of C2F6. A total of eight gravimetric PFC gas standards were prepared with relative expanded uncertainties of ≤ 0.52% (≈95% confidence level). These primary standards were ultimately used to assign values to a series of secondary gas standards at three mole-fraction levels with relative expanded uncertainties ranging from ± 0.7% to 5.3% (≈95% confidence level). This series of secondary standards was used within the aluminum industry to calibrate instruments used to make emission measurements. Assignment of values to the secondary standards was performed by use of gas chromatography with flame-ionization detection (GC–FID) and Fourier transform infrared spectrometry (FTIR). Real time pot-line and stack samples from a local aluminum plant were also obtained and sub-samples sent to each participating facility for analysis. The data generated from each facility were sent to NIST for analysis. The maximum difference between the NIST and individual facilities’ values for the same sub-sample was ± 26%.

Determination of As, Cd, Cr, and Hg in SRM 2584 (Trace Elements in Indoor Dust) by high-resolution inductively coupled plasma mass spectrometry by L. L. Yu; Robert D. Vocke; Karen E. Murphy; Charles M. Beck II (pp. 834-837).
Standard reference material (SRM) 2584 (Trace Elements in Indoor Dust) was developed as a reference standard for evaluating field methods and for validating laboratory and reference methods for the assessment of lead contamination and exposure. In addition to lead, the toxic trace elements As, Cd, Cr, and Hg, at approximately 17, 10, 140, and 5 μg g–1, respectively, have been certified in the SRM. These four analytes were successfully determined by use of high-resolution inductively coupled plasma mass spectrometry (HR-ICP–MS). Isobaric interferences at masses of As and Cr were resolved by using the high resolution mode (nominal 8000) and the medium resolution mode (nominal 3000), respectively, of the instrument.The effects of a significant drift in analyte sensitivity in the course of measurement were rectified by use of internal standardization, single spike standard addition, and an optimized analysis sequence. The results were compared with those obtained by instrumental neutron activation analysis (INAA) and isotope dilution inductively coupled plasma mass spectrometry (ID-ICP–MS). The results for the quality control, SRM 2704 (Buffalo River Sediment), were in good agreement with the certified values, indicated by the uncertainty intervals of the measured values overlapping the certified intervals at 95% confidence level.

The development and certification of Standard Reference Materials® (SRMs) to assess and ensure accurate measurement of Pb in the environment by J. D. Fassett; Bruce S. MacDonald (pp. 838-842).
The National Institute of Standards and Technology (NIST) has had a major quality-assurance role in the federal effort to reduce lead poisoning of children in the United States through its mission of ensuring the accuracy of chemical measurements. NIST certifies reference materials (standard reference materials – SRMs) that are used to benchmark measurements by secondary and field methods of analysis – to ensure that decisions of great health and economic impact are soundly based on good measurement science. Over the past 10 years, in cooperation with the US Environmental Protection Agency (EPA), US Department of Housing and Urban Development (HUD), and the United States Geological Survey (USGS), NIST has prepared and certified SRMs for lead content in soil, indoor dust, and paint. The role of these materials in meeting regulatory and abatement needs is described and their certified values are summarized.

Analyte transport efficiencies in electrothermal vaporization for inductively coupled plasma mass spectrometry by Klaus-Christian Friese; U. Wätjen; Karl-Heinz Grobecker (pp. 843-849).
A modified graphite furnace for solid-sampling atomic absorption spectrometry as an electrothermal vaporizer (ETV) was coupled to a Perkin–Elmer/Sciex ELAN 6000 ICP mass spectrometer. The integrals obtained from electrothermal vaporization of aliquots containing As, Cd, Cu, Co, Fe, Mn, Pb, Se, and Zn were compared with those obtained from pneumatic nebulization of the same aqueous standard solution. The pneumatic nebulizer was calibrated by weighing the mass of aqueous aerosol trapped on a filter. With “wet plasma” conditions maintained also for measurements with the ETV and reference signals for analyte signals obtained with the calibrated pneumatic nebulization, the transport efficiency of the ETV system, e.g. the ratio of the analyte amount introduced into the plasma to that amount dosed into the vaporizer, was determined.The transport efficiency of two different tube and interface designs has been evaluated. Investigations with and without the use of trifluoromethane as reactive gas, with different furnace heating rates, and with varying gas flows were performed. In general, the tube equipped with a nozzle led to generally higher transport efficiency than the standard tube. Without trifluoromethane transport efficiencies ranged from 10% to 35% with the standard tube and from 15% to 50% with the nozzle-type tube. With addition of 2 mL min–1 trifluoromethane to the argon flow of 400 mL min–1 through the tube, transport efficiencies from 20% to 70% and from 70% to100% were achieved with the standard and nozzle-type tubes, respectively.

Determination of selenium in soils by slurry-sampling graphite-furnace atomic-absorption spectrometry with polytetrafluoroethylene as silica modifier by Ryszard Dobrowolski (pp. 850-854).
A 6% slurry of polytetrafluoroethylene (PTFE) in 4% hydrofluoric acid and 1% nickel nitrate were used as modifiers for determination of selenium in soils by GF AAS. PTFE was used to remove silica from the soil sample, because this resulted in severe matrix effects. The temperature of fluorination, determined thermogravimetrically, was 600 °C. The yield of fluorination depends on the molar ratio of PTFE/silica, particle size, and the time and temperature of fluorination. The soil samples were pretreated with a small amount of concentrated hydrofluoric acid placed directly in the cup of autosampler. The results for the determination of selenium in the reference soil materials by means of the slurry-sampling technique and use of aqueous standards are in good agreement with the certified values.

Direct determination of silicon in powdered aluminium oxide by use of slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry by H. Minami; Tomomi Yoshida; Kentaro Okutsu; Qiangbin Zhang; Sadanobu Inoue; Ikuo Atsuya (pp. 855-859).
A direct method for determination of silicon in powdered high-purity aluminium oxide samples, by slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry (GF-AAS), has been established. A slurry sample was prepared by 10-min ultrasonication of a powdered sample in an aqueous solution containing both sodium carbonate and boric acid as a mixed flux. An appropriate portion of the slurry was introduced into a pyrolytic graphite furnace equipped with a platform. Silicon compounds to be determined and aluminium oxide were fused by the in situ fusion process with the flux in the furnace under optimized heating conditions, and the silicon absorbance was then measured directly. The calibration curve was prepared by use of a silicon standard solution containing the same concentration of the flux as the slurry sample. The accuracy of the proposed method was confirmed by analysis of certified reference materials. The proposed method gave statistically accurate values at the 95% confidence level. The detection limit was 3.3 μg g–1 in solid samples, when 300 mg/20 mL slurry was prepared and a 10 μL portion of the slurry was measured. The precision of the determination (RSD for more than four separate determinations) was 14% and 2%, respectively, for levels of 10 and 100 μg g–1 silicon in aluminium oxide.

Preconcentration by coprecipitation of arsenic and tin in natural waters with a Ni–pyrrolidine dithiocarbamate complex and their direct determination by solid-sampling atomic-absorption spectrometry by Q. Zhang; H. Minami; S. Inoue; I. Atsuya (pp. 860-864).
A method for the determination of trace amounts of arsenic and tin in natural waters is described. Trace amounts of arsenic and tin were preconcentrated by coprecipitation with a Ni–ammonium pyrrolidine dithiocarbamate (APDC) complex. The coprecipitates obtained were directly analyzed by graphite-furnace atomic-absorption spectrometry (GFAAS) using the Ni–APDC complex solid-sampling technique. The coprecipitation conditions used for the trace amounts of arsenic and tin in natural water were investigated in detail. It was found that arsenic and tin at sub-ng mL–1 levels were both coprecipitated quantitatively by Ni(PDC)2 in the pH range 2–3. The concentration factors by coprecipitation reached approximately 40,000 when 2 mg nickel was added as a carrier element to 500 mL of the water sample. The proposed method has been applied to the determination of trace amounts of arsenic and tin in river water and seawater reference materials, and the detection limits for arsenic and tin, which were calculated from three times of the standard deviation of the procedural blanks, are 0.02 ng mL–1 and 0.04 ng mL–1, respectively, for 500-mL volumes of water sample.

Speciation studies by capillary electrophoresis – distribution of rhodium(III) complexed forms in acidic media by S. S. Aleksenko; A. P. Gumenyuk; S. P. Mushtakova; A. R. Timerbaev (pp. 865-871).
The feasibility of capillary electrophoresis for distinguishing between the rhodium(III) species occurring in different acidic environments has been demonstrated. The separation was optimum under acidic electrolyte conditions in which the complexed Rh species were at their most stable and the electroosmotic flow approached zero, thereby aiding resolution. Identification of the forms of Rh and estimation of their relative equilibrium content were accomplished by use of a diode-array detector. The distribution of the metal complexes was highly dependent on the nature and concentration of the acid and the age of the rhodium stock solutions. On dilution Rh(III) tends to be readily hydrolyzed, giving rise to a wider variety (and a varied distribution) of complexed forms. In 0.1 mol L–1 HCl, four differently charged chloro complexes – RhCl4(H2O)2 –, RhCl3(OH)(H2O)2 –, RhCl3(H2O)3, and RhCl2(H2O)4 + –  were separated and identified. When a stock solution in 11 mol L–1 HCl was run, Rh produced a major peak ascribed to RhCl6 3–and two slowly migrating peaks from ions in which one or two of the chloride ligands were probably replaced by water and hydroxyl ion, as a result of hydrolysis. The aquatic cationic species were found to be predominant in HClO4 and HNO3 solutions, whereas only negatively charged forms of Rh(III) occurred in sulfuric acid. This speciation information opens also new possibilities of assessing the catalytic activity of Rh in kinetic reactions.

Simultaneous determination of butyltin and phenyltin species in sediments using ultrasound-assisted leaching by J. Carpinteiro; I. Rodríguez; R. Cela (pp. 872-877).
A fast and simple procedure is presented for the simultaneous leaching of butyl (mono, di and tributyl) and phenyl organotin species from sediment samples. Leached compounds are further ethylated with sodium tetraethylborate in aqueous medium, and analyzed by gas chromatography. After testing the stability of triphenyltin under different extraction conditions, ultrasound-assisted leaching at room temperature in the presence of acetic acid was been proposed as an extraction procedure compatible with the simultaneous determination of phenyl- and butyltin compounds in sediments. Recoveries between 70 and 90% were obtained for phenyl species in spiked samples prepared in the laboratory. Results for butyltin species were validated by use of the reference material PACS-2. Quantification limits, using GC–MIP–AES as measurement technique, were approximately 5–10 ng g–1. Precision in the consecutive analysis of three sediment samples varied between 3 and 10%.

Study of an Au colloid self-assembled electrode and its application to the determination of carbon monoxide by Guoyue Shi; M. Luo; Jian Xue; Fang Xu; L. Jin; Jiye Jin (pp. 878-882).
A novel electrochemical sensor has been developed for the detection of carbon monoxide. The chemically modified electrode, prepared by reaction of cysteine and then an Au colloid of size approximately 15 nm with a platinum microelectrode, has excellent catalytic activity toward carbon monoxide, with an oxidation potential of +600 mV relative to the Ag/AgCl electrode. The CO gas sensor is based on an Au colloid self-assembled modified electrode as working electrode, an Ag/AgCl electrode as reference electrode, a Pt electrode as counter electrode, and a porous film which is in direct contact with the gas-containing atmosphere. The effects on the determination of CO of different internal electrolyte solutions of perchloric acid, hydrochloric acid, sulfuric acid, nitric acid, and phosphate buffer of different concentrations were also studied. The sensor is characterized by a short response time and highly reproducible detection of CO. This sensor can be used in the field of environmental monitoring and control.

Towards an understanding of solvent extraction – electroanalytical characterization of chloride-leaching solutions by A. P. Paiva; L. M. Abrantes (pp. 883-886).
Solvent extraction has been employed to purify media simulating chloride-leaching solutions resulting from complex sulfide concentrate processing, and cyclic voltammetry (CV) has been chosen to characterize those hydrometallurgical aqueous phases. The possibilities of the CV technique were investigated by the evaluation of the adequacy of a specific organic extractant, triisobutylphosphine sulfide, aimed to efficiently and selectively extract silver from a complex chloride medium, additionally containing tenfold to 40-fold molar concentrations of iron, copper and lead. The influence of the oxidation state of the metallic ions present in the feed solution, namely Cu(II) and Cu(I), is considered. The possibilities of CV analysis for the characterization of stripping solutions are also illustrated.

Characterization of ligand sites on natural sediment particles by Vincenzo Zelano; M. Gulmini; Enrico Prenesti; Pier Giuseppe Daniele (pp. 887-892).
Organic and inorganic ligand sites on sediment particles were alkalimetrically titrated using a glass electrode as indicating device. Data obtained for suspensions containing known masses of sediment were used to calculate the concentration of surface ligand sites and their stability constants for complex formation with proton and copper(II) ion. The relationship between the concentration of ligand sites and the concentrations of metals (Cd, Cr, Cu, Fe, Mn, Pb, and Zn) and of C, N, and S was used to try to discriminate between the contributions of organic and inorganic components to the total ligand capacity of the sediment. The reliability of the chemical model deduced from potentiometric data was checked by comparing calculated values for aqueous copper(II) as a function of pH with values experimentally determined via atomic absorption spectrometry. The procedure proposed might contribute to the modeling of sediment–contaminant interaction, providing information on the nature of the ligands involved.

Membrane-controlled reagent-delivery systems – a new approach for the continuous production of reagent and standard solutions by H. Albus; B. Neidhart (pp. 893-898).
A new simple and robust system for the production of standard solutions, based on the mass-transfer of analytes through membranes, is described. The device consists of a cone-shaped reservoir vessel, filled with a concentrated solution of the analyte and separated from a liquid acceptor stream by a membrane. Mass-flow from donor to acceptor solution is controlled by the mass-transfer-affecting properties of the active membrane area, which is determined by the hole in a template (diameter 0.8 mm) placed between the membrane and the acceptor-channel. Using nitrate as model analyte and a track-etched membrane filter (pore size 0.1 μm) dilution factors up to 2,400,000 with long-term reproducible accuracy of < 2% have been achieved. Adjustment of a requested concentration is possible by varying either the flow rate of the acceptor stream or the concentration of the reservoir solution.

Investigation of infrared calibration methods for application to the study of methyl methacrylate polymerization by B. Kaczmarczyk; Barbara Morejko-Buż; Andrzej Stolarzewicz (pp. 899-903).
Infrared spectroscopy has been used to monitor the polymerization of methyl methacrylate. Concentrations of methyl methacrylate in the reaction mixture were determined by use of three calibration methods. Classical quantitative analysis was used to measure the height of the stretching vibration bands of the vinyl group at 1639 cm–1. A calibration procedure using the considerably higher intensity of the C = O stretching vibration band of the carbonyl ester group at 1725 cm–1 seemed useful only for high concentrations of methyl methacrylate, i.e. at the beginning of reaction, because this band overlaps that of poly(methyl methacrylate). Use of second-derivative spectra and measuring their values at 1725 cm–1 enabled estimation of ten times lower concentrations of methyl methacrylate the calibration using the band from the vinyl group.

In-situ separation of chromium(III) and chromium(VI) and sequential ETV–ICP–AES determination using acetylacetone and PTFE as chemical modifiers by Yingliang Wu; Bin Hu; Tianyou Peng; Zucheng Jiang (pp. 904-908).
Electrothermal vaporization–inductively coupled plasma–atomic emission spectrometry (ETV–ICP– ES) has been used for the sequential determination of Cr(III) and Cr(VI). The method is based on the difference between the chelate reactions of the two Cr species and acetylacetone. Cr(III) chelate was separated from Cr(VI) and determined with use of acetylacetone as chemical modifier. The retained Cr(VI) in graphite tube was analyzed subsequently, after addition of polytetrafluoroethylene (PTFE) as chemical modifier. The different factors affecting the vaporization behavior of Cr(III) acetylacetonate were investigated in detail. The detection limits for Cr (III) and Cr(VI) were 0.56 and 1.4 ng mL–1, respectively, and relative standard deviations for 0.1 μg mL–1 Cr(III) and 0.1 μg mL–1 Cr(VI) were 2.5% (n = 6) and 4.8% (n = 6), respectively. The linear ranges of the calibration curve for both Cr(III) and Cr(VI) covered three orders of magnitude. The proposed method was used to analyze water samples with satisfactory results.

Use of chelating resins and inductively coupled plasma mass spectrometry for simultaneous determination of trace and major elements in small volumes of saline water samples by Céline Guéguen; Janusz Dominik; Didier Perret (pp. 909-912).
For some saline environments (e.g. deeply percolating groundwater, interstitial water in marine sediments, water sample collected after several steps of fractionation) the volume of water sample available is limited. A technique is presented which enables simultaneous determination of major and trace elements after preconcentration of only 60 mL sample on chelating resins. Chelex-100 and Chelamine were used for the preconcentration of trace elements (Cd, Cu, Pb, Zn, Sc) and rare earth elements (La, Ce, Nd, Yb) from saline water before their measurement by inductively coupled plasma mass spectrometry. Retention of the major elements (Na, Ca, Mg) by the Chelamine resin was lower than by Chelex; this enabled their direct measurement in the solution after passage through the resin column. For trace metal recoveries both resins yield the same mass balance. Only Chelex resin enabled the quantitative recovery of rare earth elements. The major elements, trace metals and rare earth elements cannot be measured after passage through one resin only. The protocol proposes the initial use of Chelamine for measurement of trace and major elements and then passage the same sample through the Chelex resin for determination of the rare earth elements. The detection limit ranged from 1 to 12 pg mL–1. At concentrations of 1 ng mL–1 of trace metals and REE spiked in coastal water the precision for 10 replicates was in the range of 0.3–3.4% (RSD). The accuracy of the method was demonstrated by analyzing two standard reference waters, SLRS-3 and CASS-3.

Pressurized-fluid extraction (PFE) of chlorinated paraffins from the biodegradable fraction of source-separated household waste by Marie-Louise Nilsson; Monica Waldebäck; Gustav Liljegren; Henrik Kylin; Karin E. Markides (pp. 913-918).
A method is presented in which pressurized-fluid extraction (PFE) is used for the extraction of chlorinated paraffins (CP) from the biodegradable fraction of source-separated household waste. The conditions that were optimized for high recovery in the extraction procedure were extraction time, temperature, and the use of different solvents and different sample particle sizes. Recoveries of CP from fortified household waste material were over 90%, with only few interferences when cyclohexane was used as solvent. Extraction yields from contaminated samples containing CP were further compared with recoveries obtained by use of Soxtec extraction. The results showed that PFE is a rapid, low-solvent-consuming technique, giving high yields.

Simultaneous determination of composition of human urinary calculi by use of artificial neural networks by I. Kuzmanovski; Zlatko Zografski; Mira Trpkovska; Bojan Šoptrajanov; Viktor Stefov (pp. 919-923).
A new chemometric method, which uses artificial neural networks (ANN), is presented for determination of the composition of urinary calculi. The selected constituents were whewellite, weddellite, and uric acid from which approximately 40 % of the urinary calculi obtained from Macedonia patients are composed. The results for the synthetic mixtures were better then those obtained by partial least squares (PLS) regression or by the principal component regression (PCR), because neural networks have better prediction capacity. The generalization abilities of the optimized neural networks were checked using the standard addition method on carefully selected real natural samples.

Fluorine determination in human and animal bones by particle-induced gamma-ray emission by Ch. S. Sastri; Venkatesh Iyengar; Gilbert Blondiaux; Yves Tessier; Hermann Petri; Peter Hoffmann; Namik K. Aras; Vladimir Zaichick; Hugo M. Ortner (pp. 924-929).
Fluorine was determined in the iliac crest bones of patients and in ribs collected from post-mortem investigations by particle-induced gamma-ray emission based on the 19F(p,p′γ)19F reaction, using 2.0/2.5 MeV protons. The results indicate that for 68% of the human samples the F concentration is in the range 500–1999 μg g–1. For comparison purposes fluorine was also determined in some animal bones; in some animal tissues lateral profiles of fluorine were measured.

Application of a novel micro-injector in the determination of indole derivatives in the rat pineal gland by capillary electrophoresis with electrochemical detection by Gang Chen; Jieshi Cheng; Jiannong Ye (pp. 930-934).
A novel micro-injector has been fabricated for capillary electrophoresis (CE). It was successfully used for the determination of some indole derivatives for example melatonin (MT), serotonin (5-HT), tryptophan (Trp), and 5-hydroxy-tryptophane (5-HTrp) in the rat pineal gland by capillary electrophoresis with electrochemical detection (CE–EC). CE was performed in 0.20 mol L–1 phosphate buffer (pH 8.0). The compounds investigated can be well separated and detected within 15 min. The working electrode used was a 300-μm diameter carbon electrode positioned opposite the outlet of the capillary. The relationship between peak current and analyte concentration was highly linear in the range from 0.10 to 500 μmol L–1; detection limits (S/N = 3) were 0.03–0.13 μmol L–1. The proposed method has been successfully used to analyze real biological samples.

Estimation of the minimum uncertainty of DNA concentration in a genetically modified maize sample candidate certified reference material by J. Prokisch; R. Zeleny; S. Trapmann; L. Le Guern; H. Schimmel; G. N. Kramer; J. Pauwels (pp. 935-939).
Homogeneity testing and the determination of minimum sample mass are an important part of the certification of reference materials. The smallest theoretically achievable uncertainty of certified concentration values is limited by the concentration distribution of analyte in the different particle size fractions of powdered biological samples. This might be of special importance if the reference material is prepared by dry mixing, a dilution technique which is used for the production of the new and third generation of genetically modified (GMO) plant certified reference materials. For the production of dry mixed PMON 810 maize reference material a computer program was developed to calculate the theoretically smallest uncertainty for a selected sample intake. This model was used to compare three differently milled maize samples, and the effect of dilution on the uncertainty of the DNA content of GMO maize was estimated as well. In the case of a 50-mg sample mass the lowest achievable standard deviation was 2% for the sample containing 0.1% GMO and the minimum deviation was less than 0.5% for the sample containing 5% GMO.

Determination of antifouling pesticides and their degradation products in marine sediments by means of ultrasonic extraction and HPLC–APCI–MS by K. Martínez; D. Barceló (pp. 940-945).
A method has been developed for the simultaneous determination of antifouling pesticides and some of their degradation products, e.g. dichlofluanid, diuron, demethyldiuron, 1-(3,4-dichlorophenyl)urea, sea-nine, Irgarol 1051 and one of its metabolites (2-methylthio-4-tert-butylamino-s-triazine) in marine sediments. The determination of these compounds in sediment samples was performed by means of methanolic ultrasonic extraction then clean-up on an Isolute ENV+ solid phase extraction (SPE) cartridge. The resulting extract was then analyzed by reversed-phase high-performance liquid chromatography coupled with atmospheric-pressure chemical-ionization mass spectrometry in negative and positive ion modes (HPLC–APCI–MS). Recovery ranged from 54–109% for the antifouling agents and their degradation products. The determination limits for the different compounds varied between 0.2 and 1.6 μg kg–1 dry sediment.The analytical procedure was successfully applied to the determination of these pesticides and their degradation products in marine sediment samples from different marinas of the Catalan coast. The compounds detected were: diuron, dichlofluanid, demethyldiuron, sea-nine, and Irgarol 1051. The highest concentrations were those of diuron and Irgarol 1051 – 136 and 88 μg kg–1, respectively.

Determination of penconazole on personal protection equipment after field applications by M. Goumenou; K. Machera (pp. 946-950).
A simple analytical method, validated in-house and intra-laboratory, has been developed for the determination of penconazole on personal protection equipment (PPE) used by operators during field applications of Topas 20EW. The analytical determination of penconazole was performed by GC–ECD. Sample preparation was based on a liquid extraction procedure. The possible effect of different personal protection equipment matrices on the analytical determination of penconazole was studied and evaluated with regression analysis. No evidence of significant (at 95% CI level) effect was observed at several fortification levels. The percentage recovery of penconazole from the different PPE was in the range 59–100% with adequate correlation with the level of fortification (r2>0.99). The RSD% was in the range of 1–15% and the LOD and LOQ for penconazole were 0.84 and 2.5 ng mL–1, respectively.

Comparison of the chiral resolution of econazole, miconazole, and sulconazole by HPLC using normal-phase amylose CSPs by H. Y. Aboul-Enein; Imran Ali (pp. 951-955).
Resolution of the enantiomers of (±)-econazole, (±)-miconazole, and (±)-sulconazole has been achieved on different normal-phase chiral amylose columns, Chiralpak AD, AS, and AR. The mobile phase used was hexane–2-propanol–diethylamine, 400:99:1 (v/v). The flow rates of the mobile phase used were 0.50 and 1.00 mL min–1. The α values for the resolved enantiomers of econazole, miconazole, and sulconazole on the chiral phases were in the range 1.63 to 1.04; the Rs values varied from 5.68 to 0.32.

Covalent modification of glassy carbon electrodes with glycine for voltammetric separation of dopamine and ascorbic acid by L. Zhang; X. Lin (pp. 956-962).
Glycine was covalently grafted on to a glassy carbon electrode (GCE) by amine cation radical formation in electrooxidation of the amino-containing compound. X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry proved the immobilization of glycine on the GCE. The modified electrode reduced the overpotentials of dopamine (DA) and ascorbic acid (AA) by approximately 0.15 V and 0.23 V, respectively, and resolved the overlapping voltammetric response of DA and AA into two well-defined voltammetric peaks in cyclic voltammetry (CV) or differential pulse voltammetry (DPV), unlike the unmodified GCE; this can be used for the simultaneous determination of these species in a mixture. The differential pulse peak current was linearly dependent on DA and AA concentration in the range 5 × 10–6– 8 × 10–4 mol L–1 and 6 × 10–5– 4 × 10–3 mol L–1, with correlation coefficients of 0.996 and 0.994, respectively. The detection limits (3δ) for DA and AA were 1.8 × 10–6 mol L–1 and 2.1 × 10–5 mol L–1, respectively. The modified electrode is very sensitive, selective and stable, and has been applied to the determination of DA and AA simultaneously in samples with satisfactory results.

Electrochemical behavior and voltammetric determination of the herbicide metribuzin at mercury electrodes by J. Skopalová; K. Lemr; M. Kotouček; L. Čáp; P. Barták (pp. 963-969).
The electrochemical behavior of the herbicide metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one) at mercury electrodes was studied in aqueous solutions by direct current (DC) and tast polarography, differential pulse (DPV) and cyclic voltammetry (CV), and controlled-potential coulometry. The electrolysis products were separated and identified by chromatographic techniques combined with mass spectrometric detection. The reduction process in acid media includes two irreversible steps. In the first four-electron step the N–NH2 and the 1,6-azomethine bonds are reduced. The second step leads to the formation of 5-tert-butyl-2,3,4,5-tetrahydroimidazol-4-one at the mercury-pool electrode. The first reduction step combined with adsorptive accumulation of the herbicide molecule at the mercury electrode surface was used for its determination by differential pulse adsorptive stripping voltammetry (DPAdSV). Calibration curves were linear in the range 1–30 μg L–1 with a detection limit of 0.27 μg L–1 (1 nmol L–1) under the conditions used (buffer pH 4.5, Eacc = –0.45 V relative to Ag/AgCl and tacc = 10 s).Preconcentration on solid-phase extraction columns (SPE-phenyl) was used for the determination of very small amounts of metribuzin in river water samples. Recovery was approximately 97%. The reproducibility of the analytical procedure including SPE treatment and DPV determination was expressed as relative standard deviations of 2.53 and 3.66% for 2 and 6 μg L–1 metribuzin, respectively.

Microwave-assisted extraction of polycyclic aromatic compounds from coal by Melanie Kerst; J. T. Andersson (pp. 970-972).
Microwave-assisted extraction (MAE) of polycyclic aromatic compounds (PACs) from coal is shown to give the same pattern of compounds as Soxhlet extraction. MAE requires only 10 mL solvent and 10 min extraction time whereas Soxhlet uses 200 mL and takes 24 h. Although the yields were lower, dichloromethane (DCM) was preferred to pyridine, N-methyl-2-pyrrolidone (NMP), and NMP with CS2 because the pattern of the PACs is shown to be independent of solvent and DCM is a much more convenient solvent to work with.

Micellar electrokinetic capillary chromatography as an alternative method for the determination of dexamethasone, trimethoprim, and polymyxin B by J. M. Lemus Gallego; J. Pérez Arroyo (pp. 973-975).
A micellar electrokinetic capillary chromatographic method is presented which enables quantification of dexamethasone, polymyxin B and trimethoprim in synthetic mixtures and pharmaceutical products. Separation was carried out at 25 °C and 30 kV, with 10 mmol L–1 borate–phosphate buffer adjusted to pH 8 as electrolyte, with 50 mmol L–1 sodium dodecyl sulfate. Under these conditions separations were performed in 10 min. The limits of detection and quantification were approximately 2 mg L–1 for each component, except for polymyxin B. The method was applied to different commercial formulations.
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