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Analytical and Bioanalytical Chemistry (v.357, #6)


Once more on the account of chemical composition analysis, traceability and calibration in chemical analysis (in response to the discussion opened by Werner Hässelbarth [1, 2]) by Yuri I. Alexandrov (pp. 563-571).
This paper considers the present-day approach to traceability of measurements in chemical analysis. Specific features of concentration as a physical quantity are discussed. It is shown that the traceability of concentration measurements is the main task of metrology applications in quantitative analysis. It is proved that there is no need for a special traceability chain for measuring the properties used to identify components. The differences in the requirements for the composition measurements of standard samples and of reference materials are discussed by analysing the role played by these materials in calibration processes and accuracy checks.

Intersection point method (IPM): theoretical basis and application to spectrophotometric analyses by A. Cerdán-Vidal; A. R. Maurí-Aucejo; M. Llobat-Estellés; M. C. Pascual-Martí (pp. 572-576).
The Intersection Point Method (IPM) is a new method for the determination of an analyte in the presence of several unknown interferences. The method is based on the Apparent Content Curves (ACC) from derivative signals. To test the proposed procedure an analysis of mixtures of indicators with strong spectral overlapping was carried out. Results obtained agree with the theoretical values. Besides, the determination of caffeine in several pharmaceuticals by IPM provides good results.

On-line dilution with sequential injection analysis: a system for monitoring sulphate in industrial effluents by J. F. van Staden; R. E. Taljaard (pp. 577-581).
 On-line dilution with sequential injection analysis has been evaluated for sulphate monitoring in industrial effluents using a dilution coil in the conduits of the manifold system and a dilution step as part of the timing sequence. The manifold of the SIA system with the dilution coil is more complex than the system including the dilution step. The former method needs more complicated programming as well. Shorter analysis time favoured the dilution with the dilution step, but the limited linear range of this method is a large drawback. The large linear range of the SIA system with dilution coil makes it very suitable to be used as a process analyser. The proposed SIA system is suitable to monitor sulphate in industrial effluents in the range 50–5000 mg/L with a dilution coil, in the range 50–1000 mg/L with a timing sequence of 6.5 s and in the range 750–5000 mg/L with a timing sequence of 15 s using a dilution step; all three ranges with a RSD <4.5%.

Coulometric determination of the flow rate of small masses of substances II. Application to on-line measurement of the EOX-parameter by M. Luitjens; H. Kupka; D. Gherban; E. Baumgarten (pp. 582-588).
 Today’s microprocessor-controlled coulometric systems can generate complex functions obtained from the response of the microcoulometric cell. A previously developed procedure for determining the flow-rate (mass per unit time of detected species) has been accomplished by integrating, in the software, the full time dependence of the reaction of the coulometric cell and their electrodes, as well as of the titration curve. This leads to a time dependence of the measured signal, which has a fast response time without any delay. The titration curves are determined by means of various procedures. The applicability of the method is demonstrated for the case of the continuous analysis of the EOX-parameter (Extractable Organic Halogens X=Cl, Br, I) by coupling the coulometric detection with a FIA system. Results of continuous measurements of aqueous samples containing different chlorinated compounds as analytes are presented by taking into account different flow velocities in the FIA system as well as different measuring times. Recovery yields of the FIA system better than 70% have been obtained.

Optimized sample preparation procedures for the analysis of solid materials by total-reflection XRF by Marina Dargie; A. Markowicz; Antonella Tajani; V. Valkovic (pp. 589-593).
 The total reflection X-ray fluorescence (TXRF) method has been used for the analysis of various types of solid materials of biological, geological and environmental origin. The sample preparation step prior to TXRF measurements has been optimized for the various solid samples, including their decomposition by applying both a microwave oven and a PTFE bomb. Complete procedures for the optimized decomposition from the point of view of speed and completeness of digestion, as well as of the overall precision and accuracy are presented.

Coupling of capillary electrophoresis with ICP-MS for speciation investigations by B. Michalke; Peter Schramel (pp. 594-599).
An online hyphenation of capillary electrophoresis (CE) with inductively coupled plasma-mass spectrometry (ICP-MS) is developed, using a homemade nebulizer as the interface. The high resolution power of CE is used for the separation of metal species, whereas ICP-MS is taken for element specific detection with low detection limits. Metal species of standard solutions and real samples are separated and monitored by UV and ICP-MS. After optimization, electropherograms with high resolution were obtained, showing low detection limits around 1 μg/L (e.g. Pt-species) and very high resolution. Typical analysis times were below 22 min. Quality control aspects concerned species stability during the analytical procedure and stability of electrical current during nebulization. A possible interfering suction flow was estimated and found to be negligible.

Storage of aqueous solutions of selenium for speciation at trace level by I. Héninger; Martine Potin-Gautier; I. de Gregori; Hugo Pinochet (pp. 600-610).
 Different studies carried out in recent years on the preservation of trace selenium species in aqueous solutions are reviewed and experimental results showing a 29% oxidation of Se(IV) to Se(VI) in less than one month in acidic and oxygenated medium in the presence of chloride ions are presented. The hypothesis of an oxidation of Se(IV) to Se(VI) at acidic pH by traces of Cl2, obtained by a reaction between chloride ions and dissolved oxygen, followed by chlorine oxidation, is examined.

Certified reference materials for the quality control of EDTA- and acetic acid-extractable contents of trace elements in sewage sludge amended soils (CRMs 483 and 484) by P. Quevauviller; G. Rauret; R. Rubio; J.-F. López-Sánchez; A. Ure; J. Bacon; H. Muntau (pp. 611-618).
 The ecotoxicity and mobility of trace elements in soils are often evaluated through analytical results resulting from operationally-defined determinations (single and sequential extractions), e.g. based on EDTA, acetic acid etc. extractions. The significance and comparability of these results is highly dependent on the procedures used (standardized protocols or standards adopted by international bodies) and their quality control relies on the availability of reference materials certified following these strictly applied procedures. Recognizing the need to harmonize some of the extraction schemes currently used for soil analysis, the Measurements and Testing Programme (formerly BCR) has organized a series of interlaboratory studies, the first aim of which was to evaluate EDTA- and acetic acid-extraction procedures and the second objective was to certify reference materials for their extractable trace element contents. Two sewage amended soils have been prepared for this purpose, originating respectively from Scotland and Catalonia. This paper describes the preparation, homogeneity and stability studies, and gives an overview of the certification campaign.

Highly accurate gas chromatographic analysis of reference gases for use in vehicle emission measurements by D. Schiel; K. Röhker (pp. 619-623).
 A highly accurate gas chromatographic analytical method has been developed for the determination of the composition of gas mixtures. It was tested using a reference gas as an example consisting of 3.5% of CO, 14% of CO2, 0.2% of propane and residual N2 intended for the use in vehicle emission measurements. The method is based on comparison measurements with samples of a calibration gas, whose composition is iteratively adapted to that of the sample investigated using a gravimetric gas mixing method. For the gas chromatographic measurement, a molecular sieve column and a polymer column are used in parallel and in isothermal operation. All gas components can be determined by a single gas chromatographic measurement, and the relative uncertainty of measurement achievable is ?0.4%.

Determination of copper by anodic stripping voltammetry on a glassy carbon electrode using a continuous flow system by J. F. van Staden; M. Matoetoe (pp. 624-628).
 A successful flow-through system was developed for trace analysis of copper using DPASV with a glassy-carbon electrode. Periodical chemical regeneration of the electrode with a 1 mol/L NaOH solution increased sensitivity and precision. The method was shown to be applicable with a detection limit of 0.56 μg/L, with a determination time of less than 7 min per measurement (without deaeration time). The drawback of the system is the 10 min deaeration time. The system gave an accuracy of 0.090±0.005% for a certified reference material of low alloy steel containing 0.090±0.004% Cu. Applicability to various fresh water samples with a Cu content between 1.57 and 13.11 μg/L with an RSD<2.36% is illustrated.

Trace analysis of bromate and bromide with ion chromatography on coated reversed phase materials by U. Böhme; W. Schmidt; P. G. Dietrich; A. Matschi; F. Sacher; H.-J. Brauch (pp. 629-634).
 The ion-chromatographic method for trace analysis of bromate and bromide presented in this paper is based on coating of reversed phase (RP) material with an ionogenic agent, tetrakisdecylammonium bromide, to obtain a pseudo ion-exchange column. The analysis is carried out with usual HPLC pump and UV-detection near 200 nm. Some commercially available RP materials were tested for the coating procedure. The differences between the reversed phases are not significant. All HETP values are calculated between 0.02 and 0.14 mm. The calibration, the sensitivity of the method and the long-time stability of the coated column were tested with one selected RP material. It is shown that the simultaneous trace analysis of bromate and bromide in surface and drinking waters with chloride concentrations up to 50 mg/L is possible without any clean-up on Ag precolumns. A comparison of performance data with a determination method for bromate and bromide employing a commercially available equipment demonstrates the efficiency of the new technique.

Solvent extraction of rare-earth metals with bis(2-ethylhexyl)phosphinic acid by Y. Nagaosa; Yao Binghua (pp. 635-641).
 The extraction behavior of tervalent rare-earth metals (Ln) using a heptane solution containing bis(2-ethylhexyl)phosphinic acid (PIA-8, HR) from 0.1 mol/dm3 sodium perchlorate media was studied. The pH0.5 values and separation factors obtained were compared among the metals. The stoichiometry of the extracted species and the extraction constants for the present aqueous/heptane system were determined by slope analysis. It is demonstrated that the rare-earth metals were extracted as monomers LnR3⋅mHR (m=3, 4, 5 or 6), and the extracted species could be stripped into a relatively low concentrated hydrochloric acid. PIA-8 was found to be the most selective extractant for the mutual separation of rare-earth metals among the other phosphinic acids reported.

Rapid determination of lead, cadmium and thallium in cements using electrothermal atomic absorption spectrometry with slurry sample introduction by I. López-García; E. Navarro; P. Viñas; M. Hernández-Córdoba (pp. 642-646).
 A method is proposed for the determination of Pb, Cd and Tl in cements by ETAAS. The samples are suspended in a medium containing 10% v/v ethanol and 1% v/v both conc. nitric and hydrofluoric acids and are directly introduced into the electrothermal atomizer. The drying stage is performed by programming a 400 °C temperature, a ramp time of 5 s and a hold time of 30 s on the power supply to the atomizer. No ashing step is used. Atomization is carried out at 2100, 1800 and 1700 °C for Pb, Cd and Tl, respectively. For Cd determination, ammonium dihydrogen phosphate is added to the suspension medium. No modifier other than hydrofluoric acid is required for the Pb and Tl determination. It is shown that the results obtained by using direct calibration with aqueous standards for five commercial samples agree with those found by means of the standard additions method.

Determination of traces of uranium and thorium in (Ba, Sr) TiO3 ferroelectrics by inductively coupled plasma mass spectrometry by M. Fukuda; Yasumasa Sayama (pp. 647-651).
 Traces of uranium and thorium in barium(II), strontium(II) titanate ((Ba, Sr)TiO3) ferroelectric materials were determined by inductively coupled plasma mass spectrometry (ICP-MS). Samples were completely dissolved by a mixture of 1.4% H2O2 and 1.0 mol⋅l-1 HNO3. For a complete separation of the analytes from the matrix elements, a two step separation technique involving leaching and anion-exchange was applied. By the leaching step with HNO3 more than 90% of the matrix can be removed whereas the analytes completely remained in the solution. The anion-exchange step was carried out on a BIO⋅RAD AG1-X8 column with a mixture of 1.0 mol⋅l-1 HF and 0.5 mol⋅l-1 HNO3 as eluent. The content of uranium and thorium was subsequently measured by ICP-MS. The detection limits (D.L.) obtained were 0.043 ng g-1 and 0.035 ng g-1 for U and Th, respectively. The reproducibility was satisfactory with a relative standard deviation of less than 3% (at the 1 ng g-1 level, n=5). The matrix concentrations in the final solution were reduced to the sub-μg ml-1 level which is in the range of the detection limits of USN-ICP-AES (ultrasonic nebulization-ICP-atomic emission spectroscopy). The method was successfully applied to the determination of uranium and thorium in three synthetic (Ba, Sr)TiO3 samples spiked with the analytes at levels of 1, 5 and 10 ng g-1 and three (Ba, Sr)TiO3 ferroelectric samples containing sub-ng g-1 levels of the analytes.

Determination of the oxygen content of ceramic materials by Carrier-Gas-Heat-Extraction (CGHE) – feasibility and restrictions of the method by H. P. Beck; H. Müller (pp. 652-655).
 The oxygen content of oxides such as SiO2, ZrO2, Fe2O3, Cr2O3, Co3O4, and of Cr-, Fe- and Co-doped ZrO2 was determined by carrier-gas-heat-extraction. Special attention was given to the accuracy and the precision of the results and to the behaviour of the samples during the process of thermal decomposition. A precision of 0.5 to 1% vol could be achieved.

Determination of bismuth and lead in geological samples by electrothermal AAS Part 1. Comparative study of tungsten containing chemical modifiers by Orhan Acar; A. Rehber Türker; Ziya Kılıç (pp. 656-660).
A comparative study on the efficiency of some tungsten containing chemical modifiers such as W, W+Pd, W+Rh, W+Pt and W+Ru for thermal stabilization of Bi, In, Pb and Sb has been performed systematically by a Zeeman electrothermal atomization atomic absorption spectrometer (ETAAS). The addition of tartaric acid (TA) as a reducing agent additionally to the mixed modifiers was studied. A mixture of W+Pd+TA was found to be a powerful mixed modifier for the determination of Bi, In, Pb and Sb. Pretreatment temperatures could be increased up to 1250–1500° C using this mixed modifier. The use of the mixed modifier results in an enhanced accuracy and precision of the method and recovery rates above 97% for all samples. The W+Pd+TA mixed modifier was applied to the determination of Bi and Pb in dissolved geological reference samples.

Cation-exchange isolation and ICP-AES determination of rare earth elements in geological silicate materials by M. I. Rucandio (pp. 661-669).
An ion-exchange ICP-AES method for the determination of 14 rare earth elements (REEs) and Y in geological materials is described. The separation of REEs from Ba using a Dowex 50W-X8 cation resin is especially considered since Ba is an excellent internal standard for REE determination by this technique. Although total recovery with either HCl or HNO3 may be achieved, it is advantageous to use both acids sequentially. Volume and concentration of the acids are optimized attaining a quantitative separation of REEs from Ba by the introduction of the sample solution in a 1.75 mol/l HCl medium, followed by elution with 2 mol/l HNO3 to remove matrix elements and with 7 mol/l HNO3 to elute the analytes. The total elution volume is significantly reduced without decreasing the efficiency. The behaviour of the matrix constituents under the selected conditions is also studied, evaluating their elution percentages in each step. The final solution obtained contains only the REEs and Y, with the bulk of Sc and minor amounts of Cr, Fe, Hf and Ta. Experimental data for 5 geological reference standards (NIM-G, GSP-1, AGV-1, NIM-L and NIM-S) are reported. Good agreement between the present results and previously accepted values by various analytical techniques is observed.

Determination of reducing carbonyl groups in cellulose in the solvent system LiCl/N,N-dimethylacetamide by M. Strlic˘; Boris Pihlar (pp. 670-675).
 The 2,3,5-triphenyltetrazolium chloride (TTC) method for the determination of reducing carbonyl groups in cellulose in water suspensions has been thoroughly evaluated. By reduction of TTC in alkaline medium, triphenylformazane (formazane) is produced. It is thermally unstable and an unavoidable loss results in a relatively high detection limit for the determination of reducing carbonyl groups in most celluloses with a low content of such groups. Besides, oxidized cellulose is unstable in the alkaline media in which the reaction is performed. The determined content of reducing groups has also been shown to be affected by the amount of sample, indicating that absorption of triphenylformazane takes place. A new method for determination of reducing carbonyl groups in cellulose in homogeneous medium has been developed. Cellulose is dissolved in the solvent system LiCl/N,N-dimethylacetamide and reacts with TTC in the presence of tert-butylamine at 75 °C for 10 min and formazane is subsequently determined spectrophotometrically at 524 nm. None of the systematic errors inherent in the “aqueous” suspension method can be defined. The new procedure is also more reproducible and has a lower detection limit of 7 nmol reducing groups in a given mass of sample. The two procedures have been tested on five differently oxidised cellulose samples and the difference in the determinations are discussed.

Analysis of nitrophenols and other polar nitroaromatic compounds in ammunition wastewater by high-field proton nuclear magnetic resonance (1H-NMR) spectroscopy and chromatographic methods by A. Preiß; U. Lewin; L. Wennrich; M. Findeisen; J. Efer (pp. 676-683).
 It is shown that by using high-field proton nuclear magnetic resonance (1H-NMR) spectroscopy it is possible, without prior separation, to analyse nitrophenols and other acidic nitroaromatic compounds in the “pH 2 extract” of ammunition wastewater. The 1H-NMR chemical shifts data of a variety of reference compounds are presented. Two groundwater samples from the former ammunition plant in Elsnig (Saxony) were analysed by 1H-NMR and also by chromatographic methods (GC/MS, HPLC). The results are compared and discussed.

The high mass range time-of-flight secondary ion mass spectra of different polyarene films on silver by D. Pleul; F. Simon; H.-J. Jacobasch (pp. 684-687).
 Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to investigate thin films of poly(styrene), poly(vinyl napthalene), and poly(4-chlorostyrene) on clean silver substrate surfaces. The mass spectra were taken in the high molecular mass range (m/z>1000 amu). The different fragmentation patterns found are discussed in detail. Obviously, the fragmentation mechanisms are influenced by the electron density of the aryl rings stabilizing or destabilizing the formed cations.

Determination of zinc O,O′-dialkyl dithiophosphate lubricant additives via the corresponding methyl and p-nitrobenzylic ester derivatives using GC-MS, GC-NPD and HPLC-MS by R. Becker; W. Hoffmann; A. Knorr; W. Walther; A. Lehmann (pp. 688-694).
 A quantitative fingerprinting of automotive lubricants with respect to zinc dialkyl dithiophosphates (ZDP), major anti-wear/antioxidant additives, is presented. ZDPs in lubricant solutions are converted into the corresponding methyl and p-nitrobenzylic esters, respectively. After removal of the lubricant matrix the methyl esters are submitted to gas chromatography (GC). Mass spectrometric detection (MS) and comparison with reference methyl esters enable the characterisation of practical ZDP mixtures with respect to alkyl chain length and isomery of the single components. Overall recovery rates are higher than 90% and phosphorus-selective detection (NPD) allows a quantitative determination down to 0.1 pg/μl. The p-nitrobenzylic esters may be analysed by HPLC. Identification and quantification is performed by on-line HPLC-UV and HPLC-MS (APCI) with a determination limit of 20 pg/μl. The ZDP quantification via the methyl esters is applied to seven lubricants from the German market. The method is applicable to used oils allowing the monitoring of ZDP consumption during engine operation.

Separation of nonionic surfactants of the polyoxyethylene type by capillary electrophoresis by K. Heinig; C. Vogt; G. Werner (pp. 695-700).
 Nonionic surfactants are widely used in commercial formulations as complex mixtures requiring efficient and selective separation methods. Capillary electrophoretic separations were carried out in electrolytes containing high amounts of organic solvents and anionic surfactants based on the formation of association complexes between analytes and anionic surfactants without micelle formation. Octyl- and nonylphenol polyethoxylates were separated as their ethoxylate homologues. Influences of the electrophoretic conditions like electrolyte concentration and pH, type and content of anionic surfactant and organic solvents were investigated.

A collaborative study of 209 PCB congeners and 6 Aroclors on 20 different HRGC columns 1. Retention and coelution database by George M. Frame (pp. 701-713).
The elution orders and predicted coelutions of all 209 PCB congeners were obtained for 27 HRGC-ECD or HRGC-MS systems comprising 20 different stationary phases. The resultant database facilitates selection of the columns most suitable for developing particular comprehensive, quantitative, congener-specific PCB analyses, the design of the minimum number of congener mixtures needed to calibrate such analyses, and the testing of retention prediction algorithms based on structure relationships of GC phases and congener substitution patterns.

A collaborative study of 209 PCB congeners and 6 Aroclors on 20 different HRGC columns 2. Semi-quantitative Aroclor congener distributions by George M. Frame (pp. 714-722).
Weight percents of PCB congeners in Aroclors 1221, 1016, 1242, 1254, 1260, and 1262 were determined by separately averaging resolved peaks quantified against standards of all 209 congeners in 9 HRGC-ECD and 9 HRGC-MS systems. A separate pair of systems provided nearly complete profiles of Aroclors 1232 and 1248. The tabulated values lack sufficient accuracy to qualify the Aroclors as secondary standards for comprehensive, quantitative, congener-specific analyses, but they provide more complete and accurate semi-quantitative characterizations of congener distributions for a larger number of Aroclors than prior publications.

Characterization of three Aroclor mixtures using a new cyanobiphenyl stationary phase by B. R. Hillery; James E. Girard; M. M. Schantz; Stephen A. Wise (pp. 723-731).
 The retention characteristics of all 209 polychlorinated biphenyl (PCB) congeners were determined on a new p,p-cyanobiphenyl stationary phase using gas chromatography with electron capture detection (GC-ECD). Response factors were determined relative to decachlorobiphenyl, PCB 209. Several congeners that coelute on the phases routinely used for PCB analysis are separated on this phase, including the hexachlorobiphenyls 138, 163, and 164. The p,p-cyanobiphenyl stationary phase exhibits altered retention for planar congeners, such that the toxic coplanar PCBs 77, 126, and 169 are eluted free from interference. Of the 209 congeners, 61 were separated using the p,p-cyanobiphenyl phase in conjunction with GC-ECD. When analyzed by gas chromatography with mass selective detection (GC-MSD), the number of congeners determined increased to 133. Therefore GC-MSD was used with the p,p-cyanobiphenyl phase to characterize three PCB mixtures: Aroclor 1242, Aroclor 1254, and Aroclor 1260.

Congener-specific method for the determination of ortho and non-ortho polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in foods by carbon-column fractionation and gas chromatography-isotope dilution mass spectrometry by F. Krokos; C. S. Creaser; C. Wright; J. R. Startin (pp. 732-742).
 The chromatographic behavior of ortho and non-ortho polychlorinated biphenyls (PCBs) on supported carbon columns has been investigated and the structure-affinity relationship of activated carbon towards PCB molecules established. Optimisation of the parameters controlling the elution of PCB congeners through the carbon column led to the development of a solvent scheme for the efficient separation of (i) ortho substituted PCBs, (ii) non-ortho substituted PCBs and (iii) polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in three separate fractions. A method for the extraction, clean-up, fractionation and determination of ortho and non-ortho substituted PCBs by GC-isotope dilution MS was developed and validated by analysis of a certified reference material. Possible losses of PCBs during freeze-drying and interferences of aliphatic hydrocarbons during mass spectrometric determination of ortho substituted PCBs are also discussed.

Combination of micellar extraction and GC-ECD for the determination of polychlorinated biphenyls (PCBs) in water by B. Fröschl; G. Stangl; R. Niessner (pp. 743-746).
 The application of the solvent-free micellar extraction as an alternative method to the liquid–liquid extraction for the enrichment of polychlorinated biphenyls (PCBs) from ultrapure and natural water is presented. A nonionic surfactant was used to preconcentrate the PCBs. After a clean-up consisting of two columns (silica gel and Florisil) the analytes were identified and quantified by GC-ECD. Recoveries for spiked water were up to 100%. For highly contaminated seepage water of landfills liquid–liquid extraction is involving great problems with the phase separation of water and solvent. According to our results, the micellar extraction is superior to the liquid–liquid extraction for this difficult kind of aqueous matrix.

Correction of the interference by mixing the reagents in the bioluminescent determination of ATP in environmental samples by an interfaced PC photometer and a robust regression procedure by M. Mecozzi; Marina Amici; Giovanni Visco (pp. 747-751).
 An automated procedure for correcting the interference due to mixing the reagents in the determination of ATP by a bioluminescent technique is described. The measurements were performed by an in-house interfaced PC photometer. An automated procedure based on a robust regression method and outliers detection was applied to exclude the time of the mixing of the reagents from the global time of reaction. In fact the mixing of the reagents is responsible of the poor analytical precision (RSD%>25) and low sensitivity (limit of detection≈2×10-8 mol/l). By this procedure, the precision (RSD%<7) and sensitivity (limit of detection≈8×10-10 mol/l) were improved. The method was applied to the determination of ATP in marine sediments and good recovery within 90–108% was obtained. For non-polluted samples the measurement can be carried out by direct comparison with standard solutions. The standard addition procedure is recommended for polluted samples.

Determination of mercury(II) traces in drinking water by inhibition of an urease reactor in a flow injection analysis (FIA) system by Renbing Shi; K. Stein; Georg Schwedt (pp. 752-755).
 The integration of an urease reactor into a gas diffusion flow injection system was investigated for the determination of urease inhibitors. The enzyme was immobilized by entrapping in polyacrylamide gel. Besides copper and silver ions mercury ions inhibit the conversion of urea to carbon dioxide and ammonia catalysed by urease. The pH change of the carrier solution caused by the ammonia released was measured potentiometrically with a pH electrode. The inhibition behaviour of Hg(II) ions was investigated. A linear range from 2 to 20 μg L-1 Hg(II) was obtained after a 90 s inhibition, with a correlation coefficient of r=0.9997. The relative standard deviation was 1.4% for five measurements of 2 μg L-1Hg(II). A sample frequency of 7 h-1 was achieved. The inhibited enzyme can be reactivated. The method was applied to the determination of Hg(II) in two drinking water samples.

Assessment of organolead species in the Austrian Danube-basin using GC-MIP-AED by M. Paneli; E. Rosenberg; M. Grasserbauer; M. Ceulemans; F. Adams (pp. 756-762).
In order to evaluate the effectiveness of recent restrictions of Austrian government for the consumption of leaded gasoline, ionic organolead species were determined in 13 sampling sites of the Austrian and Slovakian Danube-basin in 4 bimonthyl sampling campaigns. Speciation analysis was performed using a rapid and sensitive method based on Grignard derivatization of the ionic organolead species and a GC-MIP-AED coupling for separation and detection. The operational variables were optimized for chromatographic resolution and detection limits. 100 ml of sample were used for the analyses and the detection limits for trimethyllead were 0.5 ng Pb l–1 and for triethyllead 0.85 ng Pb l–1. In general, absence of organolead induced pollution has been observed for most of the sampling locations and campaigns. Only the part of the river Danube between Vienna (Austria) and Bratislava (Slovakia), which is loaded by various intensive anthropogenic sources, showed in two campaigns the occurrence of very low trimethyl- and triethyllead concentrations, ranging between 1.2–12.0 ng Pb l–1 and 1.6–5.8 ng Pb l–1, respectively.

Direct methylation at the surface of Carbopack B Part I: Determination of phenolic pesticides by J. Nolte; B. Graß; F. Heimlich; D. Klockow (pp. 763-767).
 A procedure for the determination of phenolic pesticides, i.e. the hydroxybenzonitriles bromoxynil and ioxynil and the 2,4-dinitrophenol-derivatives dinoseb, dinosebacetate, dinoterb, dinoterbacetate, dinobuton, binapacryl and DNOC is presented. The herbicides with a free phenolic OH-group as well as the corresponding esters are very strongly adsorbed on Carbopack B, a special graphitized carbon black. In contrast to the esters, which can be removed almost quantitatively, the substances with a free phenolic OH-group cannot be eluted in any significant amount. This effect was used for the derivatization of the herbicides directly on Carbopack B, using diazomethane or TMSH as reagents. The derivatives were eluted with ethylacetate and identified and quantified by GC/MS.For recovery studies, water samples were spiked with the pesticides in concentrations within the range tolerated by the European Drinking Water Guideline.

Anodic voltammetric assay of the herbicide Metamitron on a carbon paste electrode by A. Arranz; M. F. Villalba; S. F. de Betoño; J. M. Moreda; J. F. Arranz (pp. 768-772).
The electrochemical oxidation of Metamitron in Britton-Robinson buffer (pH = 11.70) was examined using a silica modified carbon paste electrode (Si-MCPE). The results proved that the oxidation of Metamitron is irreversible and that the peak has adsorption characteristics. A mechanism, based on the oxidation of the amine group, is proposed. The influence of several instrumental and accumulation variables on the adsorptive stripping response has been evaluated using differential pulse (DPV) and square wave voltammetry (SWV Osteryoung’s method) as redissolution techniques; in both cases, a voltammetric peak is obtained at 0.482 V (DPV) and 0.341 V (SWV). The results from the SWV measurements lead to a poor sensitivity. On the contrary, under optimum conditions the AdS-DPV oxidation peak gave a linear response in the range 8 to 80 × 10–7 mol/l Metamitron solutions with a variation coefficient of 2.26% (4 × 10–6 mol/l, n = 10) and a detection limit of 3.7 × 10–7 mol/l. A method is proposed to determine Metamitron in natural water.

A new method for the determination of complexing agents in river water using HPLC by R. Geschke; M. Zehringer (pp. 773-776).
 An HPLC-method is described for the rapid and sensitive determination of NTA, EDTA and DTPA in surface and ground water at the sub-μg/L level. The analytes are enriched on anion-exchange cartridges, eluted with formic acid and analyzed on RP 8 columns within 6 min. Recoveries for EDTA and NTA were 110% resp. 94% at an interlaboratory test. They are significantly lowered when higher amounts of sulfate are present in the sample. Reproducibility and comparability with other methods are investigated. The new technique is faster than the well known GC-analysis.

Enzymatic interference-free assay for oxalate in urine by P. Cañizares; M. D. Luque de Castro (pp. 777-781).
A potentiometric method for the determination of oxalate in urine is proposed. It is based on the biochemical reaction catalyzed by oxalate decarboxylase/pervaporation/stopped-flow. The method affords a linear determination range between 0.03 and 0.08 mmol/l and has been successfully applied to the determination of oxalate in urine with excellent agreement of the results with those obtained by the conventional method based on precipitation/dissolution and titration. The effectiveness of the pervaporation process makes sample pretreatment other than dilution unnecessary.
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