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Analytical and Bioanalytical Chemistry (v.376, #2)

Spectroscopy Challenge 2 (pp. 143-148).

Specific and sensitive quantification of folate vitamers in foods by stable isotope dilution assays using high-performance liquid chromatography-tandem mass spectrometry by Achim Freisleben; Peter Schieberle; Michael Rychlik (pp. 149-156).

Stable isotope dilution assays were developed for the quantification of the folate vitamers 5-methyltetrahydrofolate, 5-formyltetrahydrofolate, tetrahydrofolate, 10-formylfolate and pteroylglutamic acid in food samples by using deuterated isotopomers as internal standards. Vitamers and their labeled analogues were analyzed simultaneously by HPLC/MS/MS using selected reaction monitoring, which allowed a higher specificity than other methods published previously. Sample preparation involved treatment by protease in sequence with α-amylase and rat serum deconjugase, followed by anion exchange chromatography. The detection limits for 5-methyltetrahydrofolate, 5-formyltetrahydrofolate, tetrahydrofolate, 10-formylfolate and pteroylglutamic acid were found to be 0.5, 1.2, 1.5, 0.6 and 2.6 µg/100 g fresh weight, respectively. Using the new method, folate contents were determined in meat, cereals, and vegetables. Data were in good agreement with literature data, except results for broccoli, which were much lower than reported in previous studies.

Keywords: Electrospray mass spectrometry Folates Food Liquid chromatography/tandem mass spectrometry Stable isotope dilution assay

Analysis of pesticide residues in essential oils of citrus fruit by GC–MS and HPLC–MS after solid-phase extraction by Sami Barrek; Olivier Paisse; Marie-Florence Grenier-Loustalot (pp. 157-161).

A robust reliable method for the analysis of residues of pesticides in citrus groves was developed. Residues of twelve pesticides were extracted from citrus essential oils by SPE, separated by liquid chromatography and analyzed by GC–MS. In addition, ten pesticides were extracted by SPE, separated and analyzed by electrospray HPLC–MS. In the case of lemon essential oils, all twenty residues were separated by liquid/solid extraction on a mixed Florisil–C₁₈ cartridge. The method enabled the analysis of the twenty pesticide residues at levels of 2 to 30 ppm with limits of detection ranging between 0.02 to 0.50 mg L⁻¹.

Keywords: Essential oils Citrus fruit GC–MS HPLC–MS SPE

The influence of the brewing process on the formation of biogenic amines in beers by Roberto Romero; María Gracia Bagur; Mercedes Sánchez-Viñas; Domingo Gázquez (pp. 162-167).

Biogenic amines, as dabsyl derivatives, were determined in beer samples, intermediate products, and raw materials (malt and maize) by HPLC. A procedure for the extraction of the amines from malt and maize with diluted hydrochloric acid was optimised by combining a Response Surface Methodology with a Simultaneous Decision Making Approach. The results of the analysis indicate that, in brewing, technology and hygiene are the decisive factors that determine the amine concentrations in the final product.

Keywords: Biogenic amines Beers Malt Brewing Fermentation Hygiene

Evaluation of the redox properties and anti/pro-oxidant effects of selected flavonoids by means of a DNA-based electrochemical biosensor by Ján Labuda; Miriam Bučková; Ľudmila Heilerová; Stanislav Šilhár; Ivan Štepánek (pp. 168-173).

Quercetin and rutin as well as catechin and epigallocatechin gallate were investigated, as widely distributed representatives of flavonols and flavanols, respectively, regarding their anti/pro-oxidant properties. The flavonoids are irreversibly oxidized at a dsDNA-modified screen-printed electrode within 0.368 to 0.449 V vs. SHE without binding to DNA. Using the DNA biosensor the detection scheme of a DNA prevention/degradation exploits the [Co(phen)₃]³⁺ complex as an electrochemical DNA marker. Antioxidant activity of flavonoids was tested in a model cleavage mixture composed of 5×10⁻⁷ mol L⁻¹ [Cu(phen)₂]²⁺ as the catalyst, 1×10⁻³ mol L⁻¹ ascorbic acid as the chemical reductant and atmospheric oxygen as the natural oxidant where reactive oxygen radicals are generated. The antioxidant activity increases with the concentration of flavonoids reaching a maximum where pro-oxidative behaviour becomes of importance. The pro-oxidant potency of flavonoids depends on the presence of atmospheric oxygen and follows the order quercetin>rutin>epigallocatechin gallate>catechin.

Keywords: Antioxidants Flavonoids Phytochemicals DNA biosensor Screen-printed electrode

Size fractionation of non-volatile dissolved organic compounds and metal species in German white wines by combining on-line tangential-flow multistage ultrafiltration, a home-built carbon analyser, and inductively coupled plasma mass spectrometry by Maria del Mar Castiñeira; P. Burba; N. Jakubowski; J. Andersson (pp. 174-181).

Organic metal species and their size fractions in three German white wines were characterized by combining multistage ultrafiltration (MST-UF), determination of non-volatile dissolved organic carbon (NV-DOC) by a home-built carbon analyser, and metal quantification by inductively coupled plasma mass spectrometry (ICP–MS). First, NV-DOC and metal species in selected "dry" German white wines were fractionated on-line using MST-UF in the size range of >100 kDa to <1 kDa. For this purpose a 20 mL sample of the wine under study diluted 1:10 with high-purity water was processed through a cascade system of hydrophilized polyethersulfone-based flat membranes of decreasing cut-off (100, 50, 10, 5, and 3 kDa). An aliquot of the fraction <3 kDa was additionally processed through a commercial UF tube (MidGee system, cut-off: 1 kDa) to obtain low-molecular size fractions also. A home-built carbon analyser was applied to determine NV-DOC in the wines and their size fractions. The NV-DOC found in a German reference wine and its size fractions was as follows: total NV-DOC: 8.97 mg mL⁻¹; F₁ (>100 kDa), 0.15%; F₂ (50–100 kDa), 0.44%; F₃ (10–50 kDa), 0.74%; F₄ (5–10 kDa), 0.76%; F₅ (5–3 kDa), 0.7%; F*₆ (3–1 kDa), 0.9%; F₇ (<1 kDa), 81.6% (related to total NV-DOC). The NV-DOC recovery was 85.2%. Accordingly, most of the NV-DOC in this wine consists of low-molecular mass organic compounds of <1 kDa, presumably carboxylic acids as typical in wine. Parallel metal determinations in these wines and their fractions were performed by ICP–MS. The measurements showed that the major part of the metals investigated, up to 25 elements, were dissolved in the size fraction of <1 kDa except Ba, Sr and Pb which appeared also in other fractions. In addition, conventional UV–VIS spectroscopy was applied to characterise the studied wines and their size fractions. According to this, the UV absorbance between 254 and 280 nm of these white wines shows a parallel trend to their NV-DOC.

Keywords: Wine Non-volatile dissolved organic carbon Metal species Ultrafiltration ICP–MS

In situ measurement of conformational changes in proteins at liquid interfaces by circular dichroism spectroscopy by Srinivasan Damodaran (pp. 182-188).

A new circular dichroism (CD) spectroscopy technique for studying conformational changes in proteins in situ at the air–water interface is described. By using this technique, conformations of four proteins, viz., β-casein, bovine serum albumin (BSA), lysozyme, and fibrinogen in the adsorbed state at the air–water interface have been studied. β-Casein, which is predominantly in a disordered state in solution, assumes a β-sheet conformation at the air–water interface. On the other hand, lysozyme and fibrinogen, which are α+β-type proteins in solution, become β-type proteins by completely transforming their α-helix structure into β-sheets. Bovine serum albumin, which is an α-type protein in solution, loses its α-helix and becomes a disordered protein at the air–water interface. The results indicated that during unfolding and film formation at the interface, structural changes in proteins, regardless of their initial native state, follow the course of increasing β-sheet and disordered structure and decreasing α-helix content. Although this seems to be the general trend, the exceptional case of BSA suggests, however, that this is not universal.

Keywords: Air–water interface Protein adsorption Protein conformation Circular dichroism Protein conformation at interfaces

Rapid multiresidue determination of organochlorine and organophosphorus compounds in human serum by solid-phase extraction and gas chromatography coupled to tandem mass spectrometry by E. Pitarch; R. Serrano; F. J. López; F. Hernández (pp. 189-197).

A rapid analytical method for the multiresidue determination of several organochlorine and organophosphorus pesticides and polychlorinated biphenyls in human serum samples has been developed. Analytes were isolated by solid-phase extraction using C18 cartridges with subsequent analysis by GC–MS/MS using a glass liner packed with CarboFrit in the GC injection port. Labelled surrogate internal standards (fenitrothion D6, HCB ¹³C6, p,p′-DDE D8 and PCB 138 ¹³C12) were added to the samples before the extraction and were used for quantitation and for quality control in the analysis of real-world samples. Accuracy and precision were evaluated by using serum samples fortified at two concentration levels for the three families of compounds, with satisfactory results in the majority of cases. The high selectivity and sensitivity of GC–MS/MS allowed low detection limits of 0.05–0.5 ng mL⁻¹ for most of the analytes investigated. The developed procedure improves other current methodologies for the analysis of pesticides and PCBs in biological fluids, especially as regards to analysis time and simplicity of sample treatment. The method was applied to several serum samples obtained from farmers devoted to citrus crop production. Chlorpyrifos, HCB, p,p′-DDE and the higher chlorinated PCBs (153, 138 and 180) were the most frequently detected compounds.

Keywords: Organophosphorus pesticides Organochlorine pesticides Polychlorinated biphenyls Serum samples Gas chromatography Tandem mass spectrometry

Platinum determination by inductively coupled plasma–sector field mass spectrometry (ICP–SFMS) in different matrices relevant to human biomonitoring by S. Hann; G. Koellensperger; K. Kanitsar; G. Stingeder; M. Brunner; B. Erovic; M. Müller; C. Reiter (pp. 198-204).

The analytical challenges of Pt determination by ICP–SFMS posed by different human tissues and fluids have been critically assessed. Investigated samples were (1) urine, (2) serum of cancer patients sampled during chemotherapy with carboplatin, (3) microdialysates (20 µL sample volume) collected from tumor and non-tumor tissue, and, finally—for the first time—(4) human lung tissue to study background concentrations of inhaled platinum. Sample preparation involved microwave digestion and open vessel treatment or simple dilution (microdialysates). Depending on the sample preparation and introduction systems used (microconcentric nebulization, ultrasonic nebulization with and without membrane desolvation) excellent procedural detection limits (3s criterion) of 0.35 pg g⁻¹ for urine, 420 pg g⁻¹ for serum, 400 pg g⁻¹ for lung tissue and 13 pg g⁻¹ for microdialysates could be obtained. Ultratrace concentrations of 1–40 pg g⁻¹, and 1000–3000 pg g⁻¹ were measured in urine and human lung tissue, respectively, as typical for samples in environmental studies. Quantification was carried out by IDMS and standard addition in the case of urine samples. Internal standardization could not correct for non-spectral interferences in external calibration. In the serum and microdialysates of patients during chemotherapy with carboplatin, elevated Pt levels ranging between 0.01 and 10 µg g⁻¹ were determined by external calibration (¹⁹⁵Pt isotope). For all investigated samples spectral interferences could be excluded by following different strategies. High-resolution control measurements (¹⁹⁴Pt, ¹⁹⁵Pt) were performed in the case of elevated Pt levels, i.e. for microdialysates and serum samples. An Hf/Pt ratio of 0.4 was determined in human lung samples. An HfO formation ratio of 0.2% was assessed for standard solutions at the present experimental conditions, revealing that the contribution of ¹⁷⁹Hf¹⁶O, ¹⁷⁸Hf¹⁷O, ¹⁷⁷Hf¹⁸O to the ¹⁹⁵Pt isotope signal used for quantification was not significant.

Keywords: Platinum Inductively coupled plasma–sector field mass spectrometry Urine Serum Clinical microdialysis Lung tissue

Direct electrochemistry of DNA, guanine and adenine at a nanostructured film-modified electrode by Kangbing Wu; Junjie Fei; Wen Bai; Shengshui Hu (pp. 205-209).

A nanostructured film electrode, a multi-wall carbon nanotubes (MWNT)-modified glassy carbon electrode (GCE), is described for the simultaneous determination of guanine and adenine. The properties of the MWNT-modified GCE were investigated by scanning electron microscopy (SEM) and cyclic voltammetry. The oxidation peak currents of guanine and adenine increased significantly at the MWNT-modified GCE in contrast to those at the bare GCE. The experimental parameters were optimized and a direct electrochemical method for the simultaneous determination of guanine and adenine was proposed. Using the MWNT-modified GCE, a sensitive and direct electrochemical technique for the measurement of native DNA was also developed, and the value of (G+C)/(A+T) of HCl-digested DNA was detected.

Keywords: Carbon nanotubes Guanine Adenine DNA Modified electrode

Capillary electrophoresis with field-enhanced stacking for rapid and sensitive determination of strychnine and brucine by Jiyou Zhang; Shufang Wang; Xingguo Chen; Zhide Hu; Xiao Ma (pp. 210-213).

A new capillary electrophoresis procedure with field-enhanced stacking concentration for the analysis of strychnine and brucine is established. After optimization of the separation and concentration conditions, the two alkaloids can be separated within 5 min and quantified with high sensitivity (The detection limits were 1.0 ng mL⁻¹ for strychnine and 1.4 ng mL⁻¹ for brucine). The method was useful for qualitative and quantitative analysis of strychnine and brucine in Strychnos nux-vomica L with recovery of 105.1% for strychnine and 98.4% for brucine.

Keywords: Capillary electrophoresis Field-enhanced stacking Strychnine Brucine

Carbon paste electrode modified with copper(II) phosphate immobilized in a polyester resin for voltammetric determination of l -ascorbic acid in pharmaceutical formulations by Marcos F. S. Teixeira; Luiz A. Ramos; Orlando Fatibello-Filho; Éder T. G. Cavalheiro (pp. 214-219).

A carbon paste electrode modified with copper(II) phosphate immobilized in a polyester resin (CuP-Poly) is proposed for voltammetric determination of l -ascorbic acid in pharmaceutical formulations. The modified electrode allows the detection of l -ascorbic acid at lower anodic potentials than observed at unmodified electrodes. Several parameters that can influence the voltammetric response of the proposed electrode such as carbon paste composition, pH, scan rate, and possible interference were investigated. The peak current was proportional to the concentration of ascorbic acid in the range 2.0×10⁻⁵ to 3.2×10⁻³ mol L⁻¹ with a detection limit of 1.0×10⁻⁵ mol L⁻¹. The stability and repeatability of the electrode for the determination of l -ascorbic acid are also discussed. Amperometric response was also recorded for electrocatalytic oxidation of the l -ascorbic acid. Concentrations of the vitamin C in pharmaceutical formulations (tablets) measured using the modified electrode and a titrimetric method are in agreement at the 95% confidence level and within an acceptable range of error.

Keywords: Modified carbon paste electrode Copper(II) phosphate immobilized Voltammetric determination l -Ascorbic acid

Square-wave adsorptive cathodic stripping voltammetric determination of anti-inflammatory indomethacin drug in tablets and human serum at a mercury electrode by G. B. El-Hefnawy; I. S. El-Hallag; E M. Ghoneim; M. M. Ghoneim (pp. 220-225).

Indomethacin is a non-steroidal anti-inflammatory drug possessing anti-pyretic and analgesic properties. A fully validated square-wave adsorptive cathodic stripping voltammetric procedure is described for determination of indomethacin. The procedure was based on the reduction of the C=O double bond of the drug molecule in Britton-Robinson buffer (pH 4) after its preconcentration onto the mercury electrode surface. The optimized conditions of the procedure were: frequency 120 Hz, scan increment 10 mV, pulse amplitude 50 mV, preconcentration potential −0.9 V (vs. Ag/AgCl/KCl_s) and preconcentration time 90 s. The proposed procedure was successfully applied for determination of the drug in tablets and human serum with good recoveries. The limits of detection in bulk form and human serum were 6.7 x10^-10 mol L^-1 and 8.1×10^-10 mol L^-1, respectively.

Keywords: Assay of indomethacin Tablet Human serum Cyclic voltammetry Square-wave adsorptive cathodic stripping voltammetry

Validation, using a chemometric approach, of gas chromatography–inductively coupled plasma–atomic emission spectrometry (GC–ICP–AES) for organotin determination by Sandrine Aguerre; Christophe Pécheyran; Gaëtane Lespes (pp. 226-235).

The coupling between gas chromatography (GC) and inductively coupled plasma–atomic emission spectrometry (ICP–AES) has been optimised using experimental designs. Four factors were considered in order to assist the crucial part of the coupling which is the analytes passing through the transfer line. The methodological approach based on the planning of fractional designs is described and justified according to an optimal experimentation. Then, the GC–ICP–AES-based method has been validated by means of statistical tests performed on calibration curves and evaluation of accuracy, precision and limits of detection (LOD), according to ISO standards and IUPAC recommendations. The absolute LOD are found to be quite similar to those obtained using flame photometer. Relative LOD ranged between 20 and 80 ng (Sn) L⁻¹ after liquid–liquid extraction of the analytes. When solid phase micro-extraction (SPME) is used, LOD are sub 10 ng (Sn) L⁻¹. The repeatability is 3–10%, according to the extraction used. Analyses of reference sediment, fresh and waste waters confirm the suitability and capabilities of GC–ICP–AES for organotin determination in the environment. The statistical approach has been demonstrated to be a powerful methodological tool, enhancing the experimental part by providing reliable analytical results.

Keywords: GC ICP–AES Experimental design Organotin Speciation

Speciation analysis of tellurium by solid-phase extraction in the presence of ammonium pyrrolidine dithiocarbamate and inductively coupled plasma mass spectrometry by Chunhai Yu; Qiantao Cai; Zhong-Xian Guo; Zhaoguang Yang; Soo Beng Khoo (pp. 236-242).

Under acidic conditions tellurium(IV) formed a complex with ammonium pyrrolidine dithiocarbamate (APDC). The tellurium(IV) complex was completely retained on a non-polar Isolute silica-based octadecyl (C₁₈) sorbent-containing solid-phase extraction (SPE) cartridge, while the uncomplexed Te(VI) passed through the cartridge and remained as a free species in the solution. Only partial Te(IV) was retained on the SPE cartridge for samples without addition of APDC. On the basis of different retention behaviours of the complexed Te(IV) and uncomplexed Te(VI), a simple and highly sensitive method is proposed for the determination of total tellurium and Te(VI) by SPE separation and inductively coupled plasma mass spectrometry (ICP–MS) detection. The Te(IV) concentration was calculated as the difference between total tellurium and Te(VI) concentrations. The detection limit (3σ) is 3 ng L⁻¹ tellurium. Factors affecting the separation and detection of tellurium species were investigated. Coexisting ions did not show significant interferences with the Te(IV)–APDC complex retention and the subsequent ICP–MS detection of Te. The method has been successfully applied to the tellurium speciation analysis in waters with spiked recoveries for Te(IV) and Te(VI) of 86.0–108% and 87.1–97.4%, respectively.

Keywords: Tellurium speciation Solid-phase extraction Ammonium pyrrolidine dithiocarbamate ICP–MS Water analysis

Comparison of three sequential extraction procedures used to study trace metal distribution in an acidic sandy soil by Corinne Parat; Jean Lévêque; Sylvie Dousset; Rémi Chaussod; Francis Andreux (pp. 243-247).

On an acid sandy soil contaminated with trace metals (Fe, Mn, Cu, Pb and Zn), three sequential extraction procedures were compared to determine the efficiency of the reagents used and the effects of the step order on the fractionation of metal species. In all cases, a magnesium nitrate solution (MgNIT) was previously used to extract exchangeable forms. In the first procedure (I), the next extraction step was performed with sodium acetate buffer (NaOAc), as used on calcareous soils, to dissolve active calcium carbonate. Then trace metals bound to different forms of oxi-hydroxides (NH₂OH, TAMOx and TAMAs fractions) were extracted before organic matter/sulfide oxidation with hydrogen peroxide at pH 2.0 in nitric acid medium (OMHyd). Finally, residual bound metals (RESID) in each procedure were extracted with a nitric–hydrofluoric–perchloric acid mixture. The second procedure (II) was the same as I, but without the NaOAc step, because of the absence of carbonate in the study soil. In procedure III, the NaOAc step was omitted and the oxidizable organic/sulfide fraction was extracted with sodium hypochlorite at pH 8.5 (OMOCl) before the reducible fractions. This study first showed that NaOAc may remove considerable amounts of metals (especially Mn and Zn) in other forms than exchangeable ones. Procedures II and III give similar results for Fe, Mn and Zn forms, which were mainly found in fractions of inorganic soil components, but not for Cu and Pb. Copper distribution was affected by the position of the oxidation step in the sequence. In procedure II, where the oxidation step (OMHyd) ended the sequence, Cu was mainly recovered in the TAMOx fraction. However, in procedure III, where the oxidation step (OMOCl) preceded the NH₂OH, TAMOx and TAMAs steps, Cu was found in both OMOCl and TAMOx fractions. Lead distribution varied with oxidation reagent: it was partly removed in the OMHyd fraction of procedures I and II, and to a much lower extent in the OMOCl fraction of procedure III, probably due to the alkaline pH of the reagent in the latter case.

Keywords: Sequential extraction procedure Trace metals Acidic sandy soil

Relationships between phosphorus fractionation and major components in sediments using the SMT harmonised extraction procedure by P. Pardo; J. F. López-Sánchez; G. Rauret (pp. 248-254).

Leaching procedures are one of the most widely used approaches to determine phosphorus fractionation in soils and sediments. Within the framework of the Standards, Measurements and Testing programme (SMT), an extraction protocol, based on the Williams procedure, was harmonised in order to improve reproducibility among laboratories. The so called SMT protocol was then used for the certification of a reference material (BCR 684) in five phosphorus fractions: non-apatite, apatite, inorganic, organic and total phosphorus. In the present paper, the SMT protocol has been applied to sediments of different composition (organic, calcareous and Fe-rich sediments). The P, Al, Ca, Fe and Mn contents extracted in each fraction were determined. The relations among these elements and the organic matter content in the samples were studied. The results obtained support the SMT protocol as a valuable tool for the study of phosphorus fractionation in sediments.

Keywords: Phosphorus Sediments SMT fractionation procedure Eutrophication

AES and SIMS analysis of non-metallic inclusions in a low-carbon Chromium-steel by Katharina Gammer; M. Rosner; G. Poeckl; H. Hutter (pp. 255-259).

In the final step of secondary metallurgical steel processing, calcium is added. Besides Mg, Ca is the most powerful deoxidiser and desulfurisation agent. It reacts with dissolved oxygen and sulfur and reduces oxides and sulfides thereby forming non-metallic inclusions. Within this paper we present the analysis of such inclusions in a low-carbon chromium-steel. Depending on the time of quenching of the steel sample, different structures were revealed by REM, Auger and SIMS: If the steel was quenched immediately after Ca-addition, non-metallic inclusions that appeared to have "cavities" could be detected with SEM. SIMS investigations of these particles showed ring-shaped structures and revealed that the ring is made up of Al, Ca, Mg, O and S. No secondary ions however could be retrieved from the core inside the ring, thus leaving the nature of the "cavities" unclear. If the steel sample was quenched 3 min after Ca addition, inclusions did not have a ring-shaped structure but a compact one.

Keywords: Non-metallic inclusions Low-carbon chromium-steel Ring-shaped structures SIMS AES SEM

The determination of water in crude oil and transformer oil reference materials by Sam A. Margolis; Charles Hagwood (pp. 260-269).

The measurement of the amount of water in oils is of significant economic importance to the industrial community, particularly to the electric power and crude oil industries. The amount of water in transformer oils is critical to their normal function and the amount of water in crude oils affects the cost of the crude oil at the well head, the pipeline, and the refinery. Water in oil Certified Reference Materials (CRM) are essential for the accurate calibration of instruments that are used by these industries. Three NIST Standard Reference Materials (SRMs) have been prepared for this purpose. The water in these oils has been measured by both coulometric and volumetric Karl Fischer methods. The compounds (such as sulfur compounds) that interfere with the Karl Fischer reaction (interfering substances) and inflate the values for water by also reacting with iodine have been measured coulometrically. The measured water content of Reference Material (RM) 8506a Transformer Oil is 12.1±1.9 mg kg⁻¹ (plus an additional 6.2±0.9 mg kg⁻¹ of interfering substances). The measured water content of SRM 2722 Sweet Crude Oil, is 99±6 mg kg⁻¹ (plus an additional 5±2 mg kg⁻¹ of interfering substances). The measured water content of SRM 2721 Sour Crude Oil, is 134±18 mg kg⁻¹ plus an additional 807±43 mg kg⁻¹ of interfering substances. Interlaboratory studies conducted with these oil samples (using SRM 2890, water saturated 1-octanol, as a calibrant) are reported. Some of the possible sources of bias in these measurements were identified, These include: improperly calibrated instruments, inability to measure the calibrant accurately, Karl Fischer reagent selection, and volatilization of the interfering substances in SRM 2721.

Keywords: Karl Fischer Water Crude oil Transformer oil Interfering substances Bias in laboratory measurement.

Rapid and simple determination of selenium in blood serum by inductively coupled plasma–mass spectrometry (ICP–MS) by L. Labat; B. Dehon; M. Lhermitte (pp. 270-273).

An inductively coupled plasma mass spectrometer (ICP–MS) with a rapid sample-preparative procedure was used for the determination of selenium in blood serum. Blood serum was prepared by dilution in an acidic solution consisting of nitric acid (1%), X-triton (0.1%) and 1-butanol (0.8%). A calibration curve was established for 1–40 µg mL⁻¹ (r²>0.99). The limit of detection was 0.5 µg mL⁻¹. Repeatability and intermediate precision were satisfactory with relative standard deviations (RSD) of 2.0% and 3.2%, respectively. This method was easily applied to reference materials with satisfactory accuracy. Good correlation (r²=0.96) was observed between ICP–MS and atomic absorption spectrometry (AAS) for the determination of ⁸²Se in blood serum from 23 patients. These results suggest that the sample preparative procedure coupled with ICP–MS can be used for the routine determination of ⁸²Se in human blood serum.

Keywords: Selenium Inductively coupled plasma mass spectrometry (ICP–MS) Blood serum

Introduction of high carbon content solvents into inductively coupled plasma mass spectrometry by a direct injection high efficiency nebuliser by Erik Björn; Wolfgang Frech (pp. 274-278).

A preliminary investigation on the introduction of high carbon content solvents into inductively coupled plasma mass spectrometry (ICP-MS) by a direct injection high efficiency nebuliser (DIHEN) is presented. Ethanol, hexane, toluene and a natural gas condensate were introduced using a flow injection system. The performance for determinations of total concentrations of mercury present in organic solvents as different species was evaluated. The most critical operating parameters were the nebuliser gas flow rate and amount of oxygen added to the plasma. For the DIHEN a nebuliser gas flow rate of 0.3 L min⁻¹ and 50 mL min⁻¹ of oxygen added to the plasma auxiliary gas flow gave stable conditions and high analyte sensitivity. Species recoveries for HgCl₂, CH₃HgCl, (CH₃)₂Hg and Hg⁰ in hexane were 99±4, 101±4, 95±4 and 104±7%, respectively. Detection limit for mercury in hexane was 85 pg mL⁻¹ based on 3σ of a ²⁰¹Hg-spiked blank. A gradual deposition was observed at the nebuliser tip, partly blocking the gas annulus. The rate of deposition seemed to be related to the amount of carbon introduced through the nebuliser. With the optimised conditions used in this work, the nebuliser could be used for approximately 50 hexane samples before cleaning was necessary.

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Analytical and Bioanalytical Chemistry (v.376, #2)