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Analytical and Bioanalytical Chemistry (v.390, #2)

John L. Holmes, Christiane Aubry and Paul M. Mayer: Assigning structures to ions in mass spectrometry by Dietmar Kuck (pp. 429-431).

Isotope ratios in analytical chemistry by Klaus G. Heumann; Frank Vanhaecke (pp. 433-435).

is retired Professor of Analytical Chemistry at the Johannes Gutenberg-University Mainz, Germany. Dr. Heumann’s research interests focus on development and application of analytical methods for the determination of trace elements and trace amounts of elemental species, using ICP-MS, TIMS, different types of optical atomic spectrometry, and electroanalysis as detection methods, and HPLC, CE, or capillary GC as separation methods. His research group has considerable experience in isotope dilution mass spectrometry (IDMS). They were the first to use IDMS in combination with negative thermal ionization mass spectrometry (NTI-MS) and with laser ablation ICP-MS for trace element analysis and the first to introduce online ICP-IDMS into hyphenated techniques for elemental speciation. Their method for precise NTI-MS isotope ratio measurements of osmium opened the door for the Re/Os-dating method which is now used in many geochemical laboratories all over the world. Investigations of the global distribution of alkylated heavy metals and alkylated halogens and their biogenic formation is another important research subject. Since his retirement in 2005 he has continued his research with a small group at the university and has been elected technical consultant for expert services of the German Research Council (DFG). He is also Editor of Analyical and Bioanalytical Chemistry. In 2004 he received the Clemens Winkler Medal of the Analytical Section of the German Chemical Society and at the 2007 European Winter Conference on Plasma Spectrochemistry in Taormina he was honored with the European Award for Plasma Spectrochemistry. Klaus G. Heumann is author or co-author of about 225 research papers in international journals.obtained his PhD degree in 1992 from Ghent University (Belgium). He continued carrying out scientific research as a post-doctoral fellow at the same university and also enjoyed a post-doctoral stay at the Johannes Gutenberg University of Mainz (Germany). Since 1998, Frank has been Professor of Analytical Chemistry at Ghent University. His research interests are the determination, speciation, and isotopic analysis of trace elements using ICP mass spectrometry. Special attention is devoted to the direct analysis of solid materials using both ETV-ICPMS and LA-ICPMS, chemical and high mass resolution for overcoming spectral interferences, and isotope ratio determination using single- and multi-collector ICPMS in the context of elemental assay via isotope dilution, tracer experiments with stable isotopes, and the use of small natural variations in the isotopic composition of metals and metalloids for unraveling geological and biological processes. He is (co-)author of more than 100 journal papers and of more than 200 conference presentations. He is a member of the editorial board of JAAS and of the international advisory board of Analytical and Bioanalytical Chemistry.

Isotope ratios in analytical chemistry by Klaus G. Heumann; Frank Vanhaecke (pp. 433-435).

The evolution and applications of multicollector ICPMS (MC-ICPMS) by C. B. Douthitt (pp. 437-440).

Selected isotope ratio measurements of light metallic elements (Li, Mg, Ca, and Cu) by multiple collector ICP-MS by Thomas I. Platzner; Irina Segal; Ludwik Halicz (pp. 441-450).

The unique capabilities of multiple collector inductively coupled mass spectrometry (MC-ICP-MS) for high precision isotope ratio measurements in light elements as Li, Mg, Ca, and Cu are reviewed in this paper. These elements have been intensively studied at the Geological Survey of Israel (GSI) and other laboratories over the past few years, and the methods used to obtain high precision isotope analyses are discussed in detail. The scientific study of isotopic fractionation of these elements is significant for achieving a better understanding of geochemical and biochemical processes in nature and the environment.

Keywords: Light elements; Isotope ratio; MC-ICP-MS

Selected isotope ratio measurements of light metallic elements (Li, Mg, Ca, and Cu) by multiple collector ICP-MS by Thomas I. Platzner; Irina Segal; Ludwik Halicz (pp. 441-450).

Keywords: Light elements; Isotope ratio; MC-ICP-MS

Variation in the isotopic composition of zinc in the natural environment and the use of zinc isotopes in biogeosciences: a review by Christophe Cloquet; Jean Carignan; Moritz F. Lehmann; Frank Vanhaecke (pp. 451-463).

Zinc (Zn) is a trace element that is, as a building block in various enzymes, of vital importance for all living organisms. Zn concentrations are widely determined in dietary, biological and environmental studies. Recent papers report on the first efforts to use stable Zn isotopes in environmental studies, and initial results point to significant Zn isotope fractionation during various biological and chemical processes, and thus highlight their potential as valuable biogeochemical tracers. In this article, we discuss the state-of-the-art analytical methods for isotopic analysis of Zn and the procedures used to obtain accurate Zn isotope ratio results. We then review recent applications of Zn isotope measurements in environmental and life sciences, emphasizing the mechanisms and causes responsible for observed natural variation in the isotopic composition of Zn. We first discuss the Zn isotope variability in extraterrestrial and geological samples. We then focus on biological processes inducing Zn isotope fractionation in plants, animals and humans, and we assess the potential of Zn isotope ratio determination for elucidating sources of atmospheric particles and contamination. Finally, we discuss possible impediments and limitations of the application of Zn isotopes in (geo-) environmental studies and provide an outlook regarding future directions of Zn isotope research.

Keywords: Zn isotopes; Isotopic variation; Biogeosciences; Source tracer; Fractionation mechanisms

Problems in obtaining precise and accurate Sr isotope analysis from geological materials using laser ablation MC-ICPMS by P. Z. Vroon; B. van der Wagt; J. M. Koornneef; G. R. Davies (pp. 465-476).

This paper reviews the problems encountered in eleven studies of Sr isotope analysis using laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) in the period 1995–2006. This technique has been shown to have great potential, but the accuracy and precision are limited by: (1) large instrumental mass discrimination, (2) laser-induced isotopic and elemental fractionations and (3) molecular interferences. The most important isobaric interferences are Kr and Rb, whereas Ca dimer/argides and doubly charged rare earth elements (REE) are limited to sample materials which contain substantial amounts of these elements. With modern laser (193 nm) and MC-ICPMS equipment, minerals with >500 ppm Sr content can be analysed with a precision of better than 100 ppm and a spatial resolution (spot size) of approximately 100 μm. The LA MC-ICPMS analysis of ⁸⁷Sr/⁸⁶Sr of both carbonate material and plagioclase is successful in all reported studies, although the higher ⁸⁴Sr/⁸⁶Sr ratios do suggest in some cases an influence of Ca dimer and/or argides. High Rb/Sr (>0.01) materials have been successfully analysed by carefully measuring the ⁸⁵Rb/⁸⁷Rb in standard material and by applying the standard-sample bracketing method for accurate Rb corrections. However, published LA-MC-ICPMS data on clinopyroxene, apatite and sphene records differences when compared with ⁸⁷Sr/⁸⁶Sr measured by thermal ionisation mass spectrometry (TIMS) and solution MC-ICPMS. This suggests that further studies are required to ensure that the most optimal correction methods are applied for all isobaric interferences.

Keywords: Laser ablation; MC-ICPMS; Sr isotopes; In situ analysis; Interferences

Problems in obtaining precise and accurate Sr isotope analysis from geological materials using laser ablation MC-ICPMS by P. Z. Vroon; B. van der Wagt; J. M. Koornneef; G. R. Davies (pp. 465-476).

Keywords: Laser ablation; MC-ICPMS; Sr isotopes; In situ analysis; Interferences

Lead isotopic analysis of infant bone tissue dating from the Roman era via multicollector ICP–mass spectrometry by David De Muynck; Christophe Cloquet; Elisabeth Smits; Frederik A. de Wolff; Ghylaine Quitté; Luc Moens; Frank Vanhaecke (pp. 477-486).

Archaeological samples originating from a cemetery of a Roman settlement, Pretorium Agrippinae (1st–3rd century A.D.), excavated near Valkenburg (The Netherlands) have been subjected to Pb isotopic analysis. The set of samples analysed consisted of infant bone tissue and possible sources of bone lead, such as the surrounding soil, garum, and lead objects (e.g., water pipes). After sample digestion with quantitative Pb recovery and subsequent quantitative and pure isolation of lead, the Pb isotopic composition was determined via multicollector ICP–mass spectrometry. The Pb isotope ratio results allowed distinction of three groups: bone, soil, and lead objects + garum. The ²⁰⁸Pb/²⁰⁶Pb ratio ranges were between 2.059 and 2.081 for the soils, between 2.067 and 2.085 for the bones, and between 2.087 and 2.088 for the lead objects. The garum sample is characterised by a ²⁰⁸Pb/²⁰⁶Pb ratio of 2.085. The bone group is situated on the mixing line between the soil and lead object groups, allowing the statement that diagenesis is not the main cause of the Pb found in the bones.

Keywords: Multicollector ICP–MS; Pb isotopic analysis; Bone tissue; Soil; Roman era

Identification of Marchfeld asparagus using Sr isotope ratio measurements by MC-ICP-MS by S. Swoboda; M. Brunner; S. F. Boulyga; P. Galler; M. Horacek; T. Prohaska (pp. 487-494).

This work focuses on testing and application of Sr isotope signatures for the fast and reliable authentication and traceability of Asparagus officinalis originating from Marchfeld, Austria, using multicollector inductively coupled plasma mass spectrometry after optimised Rb/Sr separation. The major sample pool comprises freeze-dried and microwave-digested asparagus samples from Hungary and Slovakia which are compared with Austrian asparagus originating from the Marchfeld region, which is a protected geographical indication. Additional samples from Peru, the Netherlands and Germany were limited in number and allowed therefore only restricted statistical evaluation. Asparagus samples from Marchfeld were harvested within two subsequent years in order to investigate the annual variation. The results show that the Sr isotope ratio is consistent within these 2 years of investigation. Moreover, the Sr isotope ratio of total Sr in soil was found to be significantly higher than in an NH₄NO₃ extract, reflecting the mobile (bioavailable) phase. The isotope composition in the latter extract corresponds well to the range found in the asparagus samples in Marchfeld, even though the concentration of Sr in asparagus shows no direct correlation to the concentration of Sr in the mobile phase of the soil. The major question was whether the ‘Marchfelder Spargel’ can be distinguished from samples from the neighbouring countries of Hungary and Slovakia. According to our findings, they can be clearly (100%) singled out from the Hungarian samples and can be distinguished from the Slovakian asparagus samples with a probability of more than 80%.

Keywords: Food authentication; Strontium isotope ratio measurements; Multicollector inductively coupled plasma mass spectrometry delimeter Asparagus; Soil

Identification of Marchfeld asparagus using Sr isotope ratio measurements by MC-ICP-MS by S. Swoboda; M. Brunner; S. F. Boulyga; P. Galler; M. Horacek; T. Prohaska (pp. 487-494).

Keywords: Food authentication; Strontium isotope ratio measurements; Multicollector inductively coupled plasma mass spectrometry delimeter Asparagus; Soil

Simultaneous determination of picogram per gram concentrations of Ba, Pb and Pb isotopes in Greenland ice by thermal ionisation mass spectrometry by Salah I. Jimi; Kevin J. R. Rosman; Sungmin Hong; Jean-Pierre Candelone; Laurie J. Burn; Claude F. Boutron (pp. 495-501).

A technique has been developed to simultaneously measure picogram per gram concentrations of Ba and Pb by isotope dilution mass spectrometry, as well as Pb isotopic ratios in polar ice by thermal ionisation mass spectrometry. $$ { ext{BaPO}}^{ + }_{{ ext{2}}} $$ and Pb⁺ ions were employed for these determinations. A calibrated mixture of enriched ²⁰⁵Pb and ¹³⁷Ba was added to the samples providing an accuracy of better than approximately 2% for Pb/Ba element ratio determinations. Interference by molecular ions in the Pb mass spectrum occurred only at ²⁰⁴Pb and ²⁰⁵Pb, but these contributions were negligible in terms of precisions expected on picogram-sized Pb samples. The technique is illustrated with measurements on Greenland firn, using a drill-core section that includes the Laki volcanic eruption of 1783–1784. The data show deviations from the element concentrations indicating volatile metal enrichments, but the Pb isotopic signature of the Laki lava could not be identified.

Keywords: TIMS; Barium; Lead isotopes; Ice cores; Laki; Volcanoes

Characterization of nuclear fuels by ICP mass-spectrometric techniques by Ines Günther-Leopold; Niko Kivel; Judith Kobler Waldis; Beat Wernli (pp. 503-510).

Isotopic analyses of radioactive materials such as irradiated nuclear fuel are of major importance for the optimization of the nuclear fuel cycle and for safeguard aspects. Among the mass-spectrometric techniques available, inductively coupled plasma mass spectrometry (ICP-MS) and thermal ionization mass spectrometry are the most frequently applied methods for nuclear applications. Because of the low detection limits, the ability to analyze the isotopic composition of the elements and the applicability of the techniques for measuring stable as well as radioactive nuclides with similar sensitivity, both mass-spectrometric techniques are an excellent amendment to classical radioactivity counting methods. The paper describes selected applications of multicollector ICP-MS in combination with chromatographic separation techniques and laser ablation for the isotopic analysis of irradiated nuclear fuels. The advantages and limitations of the selected analytical technique for the characterization of such a heterogeneous sample matrix are discussed.

Keywords: Inductively coupled plasma mass spectrometry; High-performance liquid chromatography; Laser ablation; Nuclear fuel; Isotope ratios; Fission products

Characterization of nuclear fuels by ICP mass-spectrometric techniques by Ines Günther-Leopold; Niko Kivel; Judith Kobler Waldis; Beat Wernli (pp. 503-510).

Keywords: Inductively coupled plasma mass spectrometry; High-performance liquid chromatography; Laser ablation; Nuclear fuel; Isotope ratios; Fission products

Ultratrace-level radium-226 determination in seawater samples by isotope dilution inductively coupled plasma mass spectrometry by Zsolt Varga (pp. 511-519).

An improved and novel sample preparation method for ²²⁶Ra determination in liquid samples by isotope dilution inductively coupled plasma sector field mass spectrometry using laboratory-prepared ²²⁸Ra tracer has been developed. The procedure involves a selective preconcentration achieved by applying laboratory-prepared MnO₂ resin followed by cation exchange chromatographic separation. In order to completely eliminate possible molecular interferences, medium mass resolution (R = 4,000) combined with chemical separation was found to be a good compromise that enhanced the reliability of the method. The detection limit of 0.084 fg g⁻¹ (3.1 mBq kg⁻¹) achieved is comparable to that of the emanation method or alpha spectrometry and is suitable for low-level environmental measurements. The chemical recovery of the sample preparation method ranged from 72 to 94%. The proposed method enables a rapid, accurate and less labor-intensive approach to routine environmental ²²⁶Ra determination than the radioanalytical techniques conventionally applied.

Keywords: Radium; Inductively coupled plasma mass spectrometry; Liquid samples; Seawater; Environmental analysis

Ultratrace-level radium-226 determination in seawater samples by isotope dilution inductively coupled plasma mass spectrometry by Zsolt Varga (pp. 511-519).

Keywords: Radium; Inductively coupled plasma mass spectrometry; Liquid samples; Seawater; Environmental analysis

^{239, 240, 241}Pu fingerprinting of plutonium in western US soils using ICPMS: solution and laser ablation measurements by James V. Cizdziel; Michael E. Ketterer; Dennis Farmer; Scott H. Faller; Vernon F. Hodge (pp. 521-530).

Sector field inductively coupled plasma mass spectrometry (SF-ICPMS) has been used with analysis of solution samples and laser ablation (LA) of electrodeposited alpha sources to characterize plutonium activities and atom ratios prevalent in the western USA. A large set of surface soils and attic dusts were previously collected from many locations in the states of Nevada, Utah, Arizona, and Colorado; specific samples were analyzed herein to characterize the relative contributions of stratospheric fallout vs. Nevada Test Site (NTS) plutonium. This study illustrates two different ICPMS-based analytical strategies that are successful in fingerprinting Pu in environmental soils and dusts. Two specific datasets have been generated: (1) soils are leached with HNO₃-HCl, converted into electrodeposited alpha sources, counted by alpha spectrometry, then re-analyzed using laser ablation SF-ICPMS; (2) samples are completely dissolved by treatment with HNO₃-HF-H₃BO₃, Pu fractions are prepared by extraction chromatography, and analyzed by SF-ICPMS. Optimal laser ablation and ICPMS conditions were determined for the re-analysis of archived alpha spectrometry “planchette” sources. The best ablation results were obtained using a large spot size (200 μm), a defocused beam, full repetition rate (20 Hz) and scan rate (200 μm s⁻¹); LA-ICPMS data were collected with a rapid electrostatic sector scanning experiment. Less than 10% of the electroplated surface area is consumed in the LA-ICPMS analysis, which would allow for multiple re-analyses. Excellent agreement was found between ^239+240Pu activities determined by LA-ICPMS vs. activity results obtained by alpha spectrometry for the same samples ten years earlier. LA-ICPMS atom ratios for ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu range from 0.038–0.132 and 0.00034–0.00168, respectively, and plot along a two-component mixing line (²⁴¹Pu/²³⁹Pu = 0.013 [²⁴⁰Pu/²³⁹Pu] – 0.0001; r ² = 0.971) with NTS and global fallout end-members. A rapid total dissolution procedure, followed by extraction chromatography and SF-ICPMS solution Pu analysis, generates excellent agreement with certified ^239+240Pu activities for standard reference materials NIST 4350b, NIST 4353, NIST 4357, and IAEA 385. ^239+240Pu activities and atom ratios determined by total dissolution reveal isotopic information in agreement with the LA-ICPMS dataset regarding the ubiquitous mixing of NTS and stratospheric fallout Pu sources in the regional environment. For several specific samples, the total dissolution method reveals that Pu is incompletely recovered by simpler HNO₃-HCl leaching procedures, since some of the Pu originating from the NTS is contained in refractory siliceous particles.

Keywords: Plutonium isotopes; Laser ablation; ICPMS; Nevada Test Site; Stratospheric fallout; Attic dust

Determining the isotopic compositions of uranium and fission products in radioactive environmental microsamples using laser ablation ICP–MS with multiple ion counters by Sergei F. Boulyga; Thomas Prohaska (pp. 531-539).

This paper presents the application of a multicollector inductively coupled plasma mass spectrometer (MC–ICP–MS)—a Nu Plasma HR—equipped with three ion-counting multipliers and coupled to a laser ablation system (LA) for the rapid and sensitive determination of the ²³⁵U/²³⁸U, ²³⁶U/²³⁸U, ¹⁴⁵Nd/¹⁴³Nd, ¹⁴⁶Nd/¹⁴³Nd, ¹⁰¹Ru/(⁹⁹Ru+⁹⁹Tc) and ¹⁰²Ru/(⁹⁹Ru+⁹⁹Tc) isotope ratios in microsamples collected in the vicinity of Chernobyl. Microsamples with dimensions ranging from a hundred μm to about 1 mm and with surface alpha activities of 3–38 mBq were first identified using nuclear track radiography. U, Nd and Ru isotope systems were then measured sequentially for the same microsample by LA–MC–ICP–MS. The application of a zoom ion optic for aligning the ion beams into the ion counters allows fast switching between different isotope systems, which enables all of the abovementioned isotope ratios to be measured for the same microsample within a total analysis time of 15–20 min (excluding MC–ICP–MS optimization and calibration). The ¹⁰¹Ru/(⁹⁹Ru+⁹⁹Tc) and ¹⁰²Ru/(⁹⁹Ru+⁹⁹Tc) isotope ratios were measured for four microsamples and were found to be significantly lower than the natural ratios, indicating that the microsamples were contaminated with the corresponding fission products (Ru and Tc). A slight depletion in ¹⁴⁶Nd of about 3–5% was observed in the contaminated samples, but the Nd isotopic ratios measured in the contaminated samples coincided with natural isotopic composition within the measurement uncertainty, as most of the Nd in the analyzed samples originates from the natural soil load of this element. The ²³⁵U/²³⁸U and ²³⁶U/²³⁸U isotope ratios were the most sensitive indicators of irradiated uranium. The present work yielded a significant variation in uranium isotope ratios in microsamples, in contrast with previously published results from the bulk analysis of contaminated samples originating from the vicinity of Chernobyl. Thus, the ²³⁵U/²³⁸U ratios measured in ten microsamples varied in the range from 0.0073 (corresponding to the natural uranium isotopic composition) to 0.023 (corresponding to initial ²³⁵U enrichment in reactor fuel). An inverse correlation was observed between the ²³⁶U/²³⁸U and ²³⁵U/²³⁸U isotope ratios, except in the case of one sample with natural uranium. The heterogeneity of the uranium isotope composition is attributed to the different burn-up grades of uranium in the fuel rods from which the microsamples originated.

Keywords: Laser ablation inductively coupled plasma mass spectrometry; Isotope analysis; Uranium; Fission products; Hot particles; Environmental analysis

Application of enriched stable isotopes as tracers in biological systems: a critical review by Stefan Stürup; Helle Rüsz Hansen; Bente Gammelgaard (pp. 541-554).

The application of enriched stable isotopes of minerals and trace elements as tracers in biological systems is a rapidly growing research field that benefits from the many new developments in inorganic mass spectrometric instrumentation, primarily within inductively coupled plasma mass spectrometry (ICP-MS) instrumentation, such as reaction/collision cell ICP-MS and multicollector ICP-MS with improved isotope ratio measurement and interference removal capabilities. Adaptation and refinement of radioisotope tracer experiment methodologies for enriched stable isotope experiments, and the development of new methodologies coupled with more advanced compartmental and mathematical models for the distribution of elements in living organisms has enabled a broader use of enriched stable isotope experiments in the biological sciences. This review discusses the current and future uses of enriched stable isotope experiments in biological systems.

Keywords: Bioanalytical methods; Mass spectrometry/ICP-MS; Trace elements

Application of enriched stable isotopes as tracers in biological systems: a critical review by Stefan Stürup; Helle Rüsz Hansen; Bente Gammelgaard (pp. 541-554).

Keywords: Bioanalytical methods; Mass spectrometry/ICP-MS; Trace elements

Development of a method for assessing the relative contribution of waterborne and dietary exposure to zinc bioaccumulation in Daphnia magna by using isotopically enriched tracers and ICP–MS detection by Lieve I. L. Balcaen; Karel A. C. De Schamphelaere; Colin R. Janssen; Luc Moens; Frank Vanhaecke (pp. 555-569).

In order to study the effect of anthropogenic substances on freshwater and marine ecosystems and to develop methods to derive water-quality criteria, ecotoxicological testing is required. While toxicity assessments are traditionally based on dissolved metal concentrations, assuming that toxicity is caused by waterborne metal only, it was recently pointed out that also the dietary exposure route should be carefully considered and interpreted in regulatory assessments of zinc. In this context, the aim of this experimental study was to develop a method which allows the uptake of waterborne and dietary zinc by Daphnia magna and the interaction between both exposure routes to be studied. Therefore, the setup of a dual isotopic tracer study was required. During several days, daphnids were exposed to ⁶⁷Zn and ⁶⁸Zn via the dietary and the waterborne routes, respectively, and after several time intervals the daphnids were sampled and subjected to isotopic analysis by means of inductively coupled plasma mass spectrometry (ICP–MS). In order to obtain reliable and accurate results for zinc, special care was taken to prevent contamination and to deal with the spectral interferences traditionally hindering the determination of zinc. The figures of merit of both a quadrupole-based ICP–MS instrument equipped with a dynamic reaction cell, and a sector field ICP–MS unit were studied, and it was concluded that by using a sector field mass spectrometer operated at medium mass resolution all interferences could be overcome adequately. Although the set-up of the exposure experiments seems to be rather simple at first sight, it was shown in this work that several (dynamic) variables can have an influence on the results obtained and on the subsequent data interpretation. The importance of these confounding factors was examined, and on the basis of preliminary calculations it became clear that not only the isotopic composition of the daphnids has to be studied—adequate monitoring of the isotopic composition of the dissolved phase and the algae during the exposure of the daphnids is also required to accurately discriminate between uptake from water and from food.

Keywords: Isotopic analysis; Tracer study; ICP–mass spectrometry; Interferences; Ecotoxicology

Measuring magnesium, calcium and potassium isotope ratios using ICP-QMS with an octopole collision cell in tracer studies of nutrient uptake and translocation in plants by J. S. Becker; K. Füllner; U. D. Seeling; G. Fornalczyk; A. J. Kuhn (pp. 571-578).

The ability of a quadrupole-based ICP-MS with an octopole collision cell to obtain precise and accurate measurements of isotope ratios of magnesium, calcium and potassium was evaluated. Hydrogen and helium were used as collision/reaction gases for ICP-MS isotope ratio measurements of calcium and potassium in order to avoid isobaric interference with the analyte ions from (mainly) argon ions ⁴⁰Ar⁺ and argon hydride ions ⁴⁰Ar¹H⁺. Mass discrimination factors determined for the isotope ratios ²⁵Mg/²⁴Mg, ⁴⁰Ca/⁴⁴Ca and ³⁹K/⁴¹K under optimized experimental conditions varied between 0.044 and 0.075. The measurement precisions for ²⁵Mg/²⁴Mg, ⁴⁰Ca/⁴⁴Ca and ³⁹K/⁴¹K were found to be 0.09%, 0.43% and 1.4%, respectively. This analytical method that uses ICP-QMS with a collision cell to obtain isotope ratio measurements of magnesium, calcium and potassium was used in routine mode to characterize biological samples (nutrient solution and small amounts of digested plant samples). The mass spectrometric technique was employed to study the dynamics of nutrient uptake and translocation in barley plants at different root temperatures (10 °C and 20 °C) using enriched stable isotopes (²⁵Mg, ⁴⁴Ca and ⁴¹K) as tracers. For instance, the mass spectrometric results of tracer experiments demonstrated enhanced ²⁵Mg and ⁴⁴Ca uptake and translocation into shoots at a root temperature of 20 °C 24 h after isotope spiking. In contrast, results obtained from ⁴¹K tracer experiments showed the highest ⁴¹K contents in plants spiked at a root temperature of 10 °C.

Keywords: Calcium; Isotope ratio measurements; ICP-QMS; Magnesium; Nutrient uptake and transport; Octopole collision/reaction cell; Plants; Potassium; Tracer experiments

Isotope pattern deconvolution as a tool to study iron metabolism in plants by José Ángel Rodríguez-Castrillón; Mariella Moldovan; J. Ignacio García Alonso; Juan José Lucena; Maria Luisa García-Tomé; Lourdes Hernández-Apaolaza (pp. 579-590).

Isotope pattern deconvolution is a mathematical technique for isolating distinct isotope signatures from mixtures of natural abundance and enriched tracers. In iron metabolism studies measurement of all four isotopes of the element by high-resolution multicollector or collision cell ICP–MS allows the determination of the tracer/tracee ratio with simultaneous internal mass bias correction and lower uncertainties. This technique was applied here for the first time to study iron uptake by cucumber plants using ⁵⁷Fe-enriched iron chelates of the o,o and o,p isomers of ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA) and ethylenediamine tetraacetic acid (EDTA). Samples of root, stem, leaves, and xylem sap, after exposure of the cucumber plants to the mentioned ⁵⁷Fe chelates, were collected, dried, and digested using nitric acid. The isotopic composition of iron in the samples was measured by ICP–MS using a high-resolution multicollector instrument. Mass bias correction was computed using both a natural abundance iron standard and by internal correction using isotope pattern deconvolution. It was observed that, for plants with low ⁵⁷Fe enrichment, isotope pattern deconvolution provided lower tracer/tracee ratio uncertainties than the traditional method applying external mass bias correction. The total amount of the element in the plants was determined by isotope dilution analysis, using a collision cell quadrupole ICP–MS instrument, after addition of ⁵⁷Fe or natural abundance Fe in a known amount which depended on the isotopic composition of the sample.

Keywords: Iron metabolism; Plants; Iron isotope ratios; Isotope pattern deconvolution; Multicollector ICP–MS

Pitfalls in compound-specific isotope analysis of environmental samples by Michaela Blessing; Maik A. Jochmann; Torsten C. Schmidt (pp. 591-603).

In the last decade compound-specific stable isotope analysis (CSIA) has evolved as a valuable technique in the field of environmental science, especially in contaminated site assessment. Instrumentation and methods exist for highly precise measurements of the isotopic composition of organic contaminants even in a very low concentration range. Nevertheless, the determination of precise and accurate isotope data of environmental samples can be a challenge. Since CSIA is gaining more and more popularity in the assessment of in situ biodegradation of organic contaminants, an increasing number of authorities and environmental consulting offices are interested in the application of the method for contaminated site remediation. Because of this, it is important to demonstrate the problems and limitations associated with compound-specific isotope measurements of environmental samples. In this review, potential pitfalls of the analytical procedure are critically discussed and strategies to avoid possible sources of error are provided. In order to maintain the analytical quality and to ensure the basis for reliable stable isotope data, recommendations on groundwater sampling, and sample preservation and storage are given. Important aspects of sample preparation and preconcentration techniques to improve sensitivity are highlighted. Problems related to chromatographic resolution and matrix interference are discussed that have to be considered in order to achieve accurate gas chromatography/isotope ratio mass spectrometry measurements. As a result, the need for a thorough investigation of compound-specific isotope fractionation effects introduced by any step of the overall analytical method by standards with known isotopic composition is emphasized. Finally, we address some important points that have to be considered when interpreting data from field investigations. Figure CSIA Principal (Carbon)

Keywords: Compound-specific isotope analysis; Gas chromatography/isotope ratio mass spectrometry; Isotope ratio monitoring; Environmental forensics; Environmental analysis; Hydrocarbons (halogenated/polycyclic)

Pitfalls in compound-specific isotope analysis of environmental samples by Michaela Blessing; Maik A. Jochmann; Torsten C. Schmidt (pp. 591-603).

The role of sulfur and sulfur isotope dilution analysis in quantitative protein analysis by Christina Rappel; Dirk Schaumlöffel (pp. 605-615).

The element sulfur is almost omnipresent in all natural proteomes and plays a key role in protein quantification. Incorporated in the amino acids cysteine and methionine, it has been served as target for many protein-labeling reactions in classic quantitative proteomic approaches based on electrospray or MALDI mass spectrometry. This critical review discusses the potential and limitations of sulfur isotope dilution analysis (IDA) by inductively coupled plasma—mass spectrometry (ICP-MS) for absolute protein quantification. The development of this approach was made possible due to the improved sensitivity and accuracy of sulfur isotope ratio measurement by ICP-MS in recent years. The unique feature of ICP-MS, compound-independent ionization, enables compound (species)-unspecific sulfur IDA. This has the main advantage that only one generic sulfur standard (i.e., one isotopically labeled sulfur spike) is required to quantify each peptide or protein in a sample provided that they are completely separated in chromatography or electrophoresis and that their identities are known. The principles of this approach are illustrated with selected examples from the literature. The discussion includes also related fields of P/S and metal/S ratio measurements for the determination of phosphorylation degrees of proteins and stoichiometries in metalloproteins, respectively. Emerging new areas and future trends such as protein derivatization with metal tags for improved sensitivity of protein detection in ICP-MS are discussed. Figure The key role of sulfur in protein quantification

Keywords: Sulfur; Quantitative protein analysis; ICP-MS; Isotope dilution analysis; Protein labeling; Metal tags; Phosphorylation degree; Metalloprotein stoichiometry

The role of sulfur and sulfur isotope dilution analysis in quantitative protein analysis by Christina Rappel; Dirk Schaumlöffel (pp. 605-615).

Keywords: Sulfur; Quantitative protein analysis; ICP-MS; Isotope dilution analysis; Protein labeling; Metal tags; Phosphorylation degree; Metalloprotein stoichiometry

Stable isotope dilution assays in mycotoxin analysis by Michael Rychlik; Stefan Asam (pp. 617-628).

The principle and applications of stable isotope dilution assays (SIDAs) in mycotoxin analysis are critically reviewed. The general section includes historical aspects of SIDAs, the prerequisites and limitations of the use of stable isotopically labelled internal standards, and possible calibration procedures. In the application section actual SIDAs for the analysis of trichothecenes, zearalenone, fumonisins, patulin, and ochratoxin A are presented. The syntheses and availability of labelled mycotoxins for use as internal standards is reviewed and specific advances in food analysis and toxicology are demonstrated. The review indicates that LC–MS applications, in particular, require the use of stable isotopically labelled standards to compensate for losses during clean-up and for discrimination due to ion suppression. As the commercial availability of these compounds continues to increase, SIDAs can be expected to find expanding use in mycotoxin analysis.

Keywords: LC–MS–MS; Mycotoxins; Ochratoxin A; Patulin; Stable isotope dilution assay; Trichothecenes

Stable isotope dilution assays in mycotoxin analysis by Michael Rychlik; Stefan Asam (pp. 617-628).

Keywords: LC–MS–MS; Mycotoxins; Ochratoxin A; Patulin; Stable isotope dilution assay; Trichothecenes

Total selenium and selenomethionine in pharmaceutical yeast tablets: assessment of the state of the art of measurement capabilities through international intercomparison CCQM-P86 by H. Goenaga-Infante; R. Sturgeon; J. Turner; R. Hearn; M. Sargent; P. Maxwell; L. Yang; A. Barzev; Z. Pedrero; C. Cámara; V. Díaz Huerta; M. L. Fernández Sánchez; A. Sanz-Medel; K. Emese; P. Fodor; W. Wolf; R. Goldschmidt; V. Vacchina; J. Szpunar; L. Valiente; R. Huertas; G. Labarraque; C. Davis; R. Zeisler; G. Turk; E. Rizzio; L. G. Mackay; R. B. Myors; D. L. Saxby; S. Askew; W. Chao; W. Jun (pp. 629-642).

Results of an international intercomparison study (CCQM-P86) to assess the analytical capabilities of national metrology institutes (NMIs) and selected expert laboratories worldwide to accurately quantitate the mass fraction of selenomethionine (SeMet) and total Se in pharmaceutical tablets of selenised-yeast supplements (produced by Pharma Nord, Denmark) are presented. The study, jointly coordinated by LGC Ltd., UK, and the Institute for National Measurement Standards, National Research Council of Canada (NRCC), was conducted under the auspices of the Comité Consultatif pour la Quantité de Matière (CCQM) Inorganic Analysis Working Group and involved 15 laboratories (from 12 countries), of which ten were NMIs. Apart from a protocol for determination of moisture content and the provision of the certified reference material (CRM) SELM-1 to be used as the quality control sample, no sample preparation/extraction method was prescribed. A variety of approaches was thus used, including single-step and multiple-step enzymatic hydrolysis, enzymatic probe sonication and hydrolysis with methanesulfonic acid for SeMet, as well as microwave-assisted acid digestion and enzymatic probe sonication for total Se. For total Se, detection techniques included inductively coupled plasma (ICP) mass spectrometry (MS) with external calibration, standard additions or isotope dilution MS (IDMS), inductively coupled plasma optical emission spectrometry , flame atomic absorption spectrometry and instrumental neutron activation analysis. For determination of SeMet in the tablets, five NMIs and three academic/institute laboratories (of a total of five) relied upon measurements using IDMS. For species-specific IDMS measurements, an isotopically enriched standard of SeMet (⁷⁶Se-enriched SeMet) was made available. A novel aspect of this study relies on the approach used to distinguish any errors which arise during analysis of a SeMet calibration solution from those which occur during analysis of the matrix. To help those participants undertaking SeMet analysis to do this, a blind sample in the form of a standard solution of natural abundance SeMet in 0.1 M HCl (with an expected value of 956 mg kg⁻¹ SeMet) was provided. Both high-performance liquid chromatography (HPLC)–ICP-MS or gas chromatography (GC)–ICP-MS and GC-MS techniques were used for quantitation of SeMet. Several advances in analytical methods for determination of SeMet were identified, including the combined use of double IDMS with HPLC-ICP-MS following extraction with methanesulfonic acid and simplified two-step enzymatic hydrolysis with protease/lipase/driselase followed by HPLC-ICP-IDMS, both using a species-specific IDMS approach. Overall, satisfactory agreement amongst participants was achieved; results averaged 337.6 mg kg⁻¹ (n = 13, with a standard deviation of 9.7 mg kg⁻¹) and 561.5 mg kg⁻¹(n = 11, with a standard deviation of 44.3 mg kg⁻¹) with median values of 337.6 and 575.0 mg kg⁻¹ for total Se and SeMet, respectively. Recovery of SeMet from SELM-1 averaged 95.0% (n = 9). The ability of NMIs and expert laboratories worldwide to deliver accurate results for total Se and SeMet in such materials (selensied-yeast tablets containing approximately 300 mg kg⁻¹ Se) with 10% expanded uncertainty was demonstrated. The problems addressed in achieving accurate quantitation of SeMet in this product are representative of those encountered with a wide range of organometallic species in a number of common matrices. Figure Looking into the quantitative speciation of selenium in pharmaceutical supplements Photo courtesy of LGC.

Keywords: Pilot study CCQM-P86; Pharmaceutical tablets; Selenised-yeast supplements; Selenomethionine; Total selenium; Isotope dilution mass spectrometry

Development of a species-specific isotope dilution GC-ICP-MS method for the determination of thiophene derivates in petroleum products by Jens Heilmann; Klaus G. Heumann (pp. 643-653).

A species-specific isotope dilution technique for accurate determination of sulfur species in low- and high-boiling petroleum products was developed by coupling capillary gas chromatography with quadrupole ICP-MS (GC-ICP-IDMS). For the isotope dilution step ³⁴S-labeled thiophene, dibenzothiophene, and mixed dibenzothiophene/4-methyldibenzothiophene spike compounds were synthesized on the milligram scale from elemental ³⁴S-enriched sulfur. Thiophene was determined in gasoline, ‘sulfur-free’ gasoline, and naphtha. By analyzing reference material NIST SRM 2296, the accuracy of species-specific GC-ICP-IDMS was demonstrated by an excellent agreement with the certified value. The detection limit is always limited by the background noise of the isotope chromatograms and was determined for thiophene to be 7 pg absolute, which corresponds to 7 ng sulfur/g sample under the experimental conditions used. Dibenzothiophene and 4-methyldibenzothiophene were determined in different high-boiling petroleum products like gas oil, diesel fuel, and heating oil. In this case a large concentration range from about < 0.04 to more than 2,000 μg g⁻¹ was covered for both sulfur species. By parallel GC-ICP-MS and GC-EI-MS experiments (EI-MS electron impact ionization mass spectrometry) the substantial influence of co-eluting hydrocarbons on the ICP-MS sulfur signal was demonstrated, which can significantly affect results obtained by external calibration but not those by the isotope dilution technique.

Keywords: Species-specific isotope dilution mass spectrometry; GC-ICP-MS; Sulfur species; Gasoline; Diesel fuel

Development of a species-specific isotope dilution GC-ICP-MS method for the determination of thiophene derivates in petroleum products by Jens Heilmann; Klaus G. Heumann (pp. 643-653).

Keywords: Species-specific isotope dilution mass spectrometry; GC-ICP-MS; Sulfur species; Gasoline; Diesel fuel

Evaluating the potential and limitations of double-spiking species-specific isotope dilution analysis for the accurate quantification of mercury species in different environmental matrices by Mathilde Monperrus; Pablo Rodriguez Gonzalez; David Amouroux; J. Ignacio Garcia Alonso; Olivier F. X. Donard (pp. 655-666).

A new double-spiking approach, based on a multiple-spiking numerical methodology, has been developed and applied for the accurate quantification of inorganic mercury (IHg) and methylmercury (MeHg) by GC–ICPMS in different environmental matrices such as water, sediments and a wide range of biological tissues. For this purpose, two enriched mercury species (²⁰¹MeHg and ¹⁹⁹IHg) were added to the samples before sample preparation in order to quantify the extents of the methylation and demethylation processes, and thereby correct the final species concentrations. A critical evaluation of the applicability of this methodology was performed for each type of matrix, highlighting its main advantages and limitations when correcting for the conversion reactions of the species throughout the whole sample preparation procedure. The double-spike isotope dilution (DSIDA) methodology was evaluated by comparing it with conventional species specific isotope dilution (IDA) when analysing both certified reference materials and environmental samples (water, biotissues and sediment). The results demonstrate that this methodology is able to provide both accurate and precise results for IHg and MeHg when their relative concentrations are not too different (ratio MeHg/IHg > 0.05), a condition that holds for most natural waters and biotissues. Significant limitations on the accurate and precise determination of the demethylation factor are however observed, especially for real sediment samples in which the relative concentrations of the species are substantially different (ratio MeHg/IHg < 0.05). A determination of the sources of uncertainty in the methylation/demethylation factors has demonstrated that the accurate and precise measurement of the isotope ratios in the species involved in the transformations is crucial when quantifying the extents of these reactions. Although the double-spike methodology is established as a reference approach that permits the correction of most analytical biases and the accurate quantification of Hg species, some limitations have been identified for the first time in this work.

Keywords: Mercury speciation; Species-specific isotope dilution; Environmental matrices

Studies on the analytical performance of a non-covalent coating with N,N-didodecyl-N,N-dimethylammonium bromide for separation of basic proteins by capillary electrophoresis in acidic buffers in 25-and 50-μm capillaries by S. Mohabbati; S. Hjertén; D. Westerlund (pp. 667-678).

Capillaries (25-and 50-μm inner diameter) coated with a double-alkyl-chain cationic surfactant N,N-didodecyl-N,N-dimethylammonium bromide (DDAB) were used for the separation of four basic standard proteins in buffers of pH 4 at various ionic strengths. The choice of buffer is critical for the analytical performance. Ammonium ions must be avoided in the buffer used in the non-covalent coating procedure owing to competition with the surfactant. Phosphate buffer gave a better separation performance than some volatile buffers; the reason seems to be a complex formation between the proteins and dihydrogenphosphate ions, which decreases tendencies for adsorption to the capillary surface. The DDAB coating was easy to produce and stable enough to permit, without recoating, consecutive separations of the proteins for up to 100 min with good precision in migration times and peak areas. A strong electroosmotic flow gives rapid separations, which is of special importance when commercial instruments are used, since the choice of the length of the capillary is restricted. Figure EOF stability in 25 micrometer i.d. capillaries. Consecutive injections of mesityloxide performed after an initial coating with 1.0

Keywords: Non-covalent coating; Anodic electroosmotic flow; Protein–buffer interaction; Zone sharpening; Validation data

The structural modification of DNA nucleosides by nonenzymatic glycation: an in vitro study based on the reactions of glyoxal and methylglyoxal with 2′-deoxyguanosine by Yuyuan Li; Menashi A. Cohenford; Udayan Dutta; Joel A. Dain (pp. 679-688).

Methylglyoxal and glyoxal are generated from the oxidation of carbohydrates and lipids, and like d-glucose have been shown to nonenzymatically react with proteins to form advanced glycation end products (AGEs). AGEs can occur both in vitro and in vivo, and these compounds have been shown to exacerbate many of the long-term complications of diabetes. Earlier studies in our laboratory reported d-glucose, d-galactose, and d/l-glyceraldehyde formed AGEs with nucleosides. The objective of this study was to focus on purines and pyrimidines and to analyze these DNA nucleoside derived AGE adducts with glyoxal or methylglyoxal using a combination of analytical techniques. Studies using UV and fluorescence spectroscopy along with mass spectrometry provided for a thorough analysis of the nucleoside AGEs and demonstrated that methylglyoxal and glyoxal reacted with 2′-deoxyguanosine via the classic Amadori pathway, and did not react appreciably with 2′-deoxyadenosine, 2′-deoxythymidine, and 2′-deoxycytidine. Additional findings revealed that methylglyoxal was more reactive than glyoxal.

Keywords: Advanced glycation end products; Maillard reaction products; Glyoxal; Methylglyoxal; 2′-Deoxyguanosine

A simplified hollow-fibre supported liquid membrane extraction method for quantification of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in urine and plasma samples by Jon Lezamiz; Thaer Barri; Jan Åke Jönsson; Kerstin Skog (pp. 689-696).

A simple and easy-to-use extraction procedure has been optimised, validated, and applied for extraction of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in urine and spiked plasma samples. PhIP is a carcinogenic and mutagenic heterocyclic aromatic amine that is formed during cooking of meat and fish. The novelty of the extraction procedure lies in using a short piece of narrow capillary-like microporous hollow-fibre (HF) membrane as extraction device. The HF membrane was filled with a few microlitres of acidic solution and the membrane pores were impregnated with an organic extraction solvent. Therefore, the technique was called hollow-fibre supported liquid membrane (HF-SLM) extraction. The HF extraction device was then supported by a syringe needle and directly immersed in urine (1.4 mL) or plasma (0.3 mL) previously made alkaline by adding 0.5 mol L⁻¹ NaOH solution to give a final volume of 1.6 mL. The operation of the HF-SLM extraction at the optimal conditions resulted in a PhIP extraction efficiency of 74% from both spiked urine and plasma, corresponding to enrichment factors of 126 and 27, respectively. For 90 min extraction time, limits of detection and quantification were, respectively, 8 and 25 pg mL⁻¹ for urine and 6 and 11 pg mL⁻¹ for plasma. Within-day repeatability (n = 6) and between-day reproducibility (n = 3) were, respectively, 5% and 13% for urine and 6% and 7% for plasma. Analysis of urine samples collected for 12 h after a volunteer had eaten 250 g well-done chicken showed the PhIP concentration was 124 ± 21 pg mL⁻¹, calculated assuming an extraction efficiency of 74%.

Keywords: Heterocyclic aromatic amines; 2-Amino-1-methyl-6-phenylimidazo[4, 5-b]pyridine (PhIP); Plasma; Urine; Hollow-fibre supported liquid membrane extraction

Direct eicosanoid profiling of the hypoxic lung by comprehensive analysis via capillary liquid chromatography with dual online photodiode-array and tandem mass-spectrometric detection by Ladislau Kiss; Yasmin Röder; Jens Bier; Norbert Weissmann; Werner Seeger; Friedrich Grimminger (pp. 697-714).

Eicosanoids are arachidonic acid-derived mediators, with partly contradictory, incompletely elucidated actions. Thus, epoxyeicosatrienoic acids (EETs) are controversially discussed as putative vasodilatative endothelium-derived hyperpolarizing factors in the cardiovascular compartment but reported as vasoconstrictors in the lung. Inconsistent findings concerning eicosanoid physiology may be because previous methods were lacking sensitivity, identification reliability, and/or have focused on special eicosanoid groups only, ignoring the overall mediator context, and thus limiting the correlation accuracy between autacoid formation and bioactivity profile. Therefore, we developed an approach which enables the simultaneous assessment of 44 eicosanoids, including all representatives of the arachidonic acid cascade, i.e., cytochrome P450, lipoxygenase, cyclooxygenase products, and free isoprostanes as in vivo markers of oxidative stress, in one 50-minute chromatographic run. The approach combines (i) source-specific sample extraction, (ii) rugged isocratic and high-sensitivity capillary liquid-chromatographic separation, and (iii) reliable dual online photodiode-array and electrospray ionization tandem mass-spectrometric identification and quantitation. High sensitivity with limits of quantification in the femtogram range was achieved by use of capillary columns with typical high peak efficiency, due to small inner diameters, and virtually complete substance transfer to the mass spectrometer, due to flow rates in the low microliter range, instead of large inner diameter columns with low chromatographic signal and only partial analyte transfer employed by previous methods. This expeditious, global and sensitive technique provides the prerequisite for new, accurate insights regarding the physiology of specific mediators, for example EETs, in the context of all relevant vasoactive autacoids under varying conditions of oxidative stress by direct comparison of all eicosanoid generation profiles. Indeed, application of comprehensive “eicoprofiling” to hypoxically ventilated rabbit lungs revealed at a glance the enhanced biosynthesis of free EETs in the overall mediator generation context, thus suggesting their hypothetical contribution to hypoxic pulmonary vasoconstriction.

Keywords: Eicosanoid profiling; Isocratic capillary liquid chromatography; Photodiode-array detection; Tandem mass-spectrometric detection; Multiple reaction monitoring; Extracted ion chromatogram

Profiling of 3,4-methylenedioxymethamphetamine by means of high-performance liquid chromatography by Bogumiła Byrska; Dariusz Zuba (pp. 715-722).

An impurity-profiling method for 3,4-methylenedioxymethamphetamine (MDMA) is presented. The impurities of interest were extracted by solid-phase extraction (SPE) on Bakerbond C₁₈ spe columns from a weakly alkaline solution (pH 8.5). Development of the extraction conditions covered selection of the buffer for dissolution of the sample and the volume of the eluent used to elute the impurities. An important part of the studies was to optimise the separation conditions, and the simplex method was used for this purpose. Cluster analysis was applied for comparison of samples and its grouping. The developed method was based on the areas of 33 selected peaks corresponding to MDMA impurities. All examined samples were correctly classified into clusters corresponding to the synthetic route.

Profiling of 3,4-methylenedioxymethamphetamine by means of high-performance liquid chromatography by Bogumiła Byrska; Dariusz Zuba (pp. 715-722).

Novel gel-based rapid test for non-instrumental detection of ochratoxin A in beer by I. Y. Goryacheva; E. Y. Basova; C. Van Peteghem; S. A. Eremin; L. Pussemier; J.-C. Motte; S. De Saeger (pp. 723-727).

A rapid easy-to-use immunoassay was optimised for the non-instrumental detection of ochratoxin A (OTA) in beer. The analytical method involves preconcentration on the immunoaffinity layer inside a column followed by direct competitive ELISA detection in the same layer. The visual cut-off value, i.e. the lowest OTA concentration resulting in no colour development, was 0.2 μg L^-1. Assay validation was performed using samples spiked with OTA. Thirty-seven naturally contaminated samples were screened with the gel-based method developed and no false-negative results were obtained. The method described offers a simple, rapid and cost-effective screening tool, thus contributing to better health protection of consumers. Figure Gel-based immunoassay of spiked beer samples.

Keywords: Immunoassay; Screening; Mycotoxin; Food control; Visual detection; Beer; Ochratoxin A

Assisted solvent extraction and ion-trap tandem mass spectrometry for the determination of polychlorinated biphenyls in mussels. Comparison with other extraction techniques by I. García; M. Ignacio; A. Mouteira; J. Cobas; N. Carro (pp. 729-737).

A selective and sensitive analytical method for determination of ten congeners of polychlorinated biphenyls (PCBs 31, 28, 52, 101, 118, 153, 105, 138, 156, and 180) in mussel samples (Mytilus galloprovincialis) based on accelerated solvent extraction (ASE) and gas chromatography–tandem mass spectrometry (GC–MS–MS) is presented in this work. Extraction conditions were optimised using a Plackett–Burman factorial design. The final extracts were analysed after cleanup on alumina columns. The optimised extraction parameters were solvent percentage, sample amount, extraction temperature, pressure, static extraction time, flush percentage, and purge time. The results suggest that PCBs 118, 105, and 180 extractions appeared affected by only one statistically significant factor, pressure, solvent percentage and static extraction time, respectively. Extraction of PCBs 138 and 156 was affected by amount of sample. PCB 138 extraction was also statistically affected by static extraction time and purge time. Quantitative recoveries (64.8–120.3%) were achieved for all PCBs and method precision (RSD < 19%) was satisfactory.

Keywords: PCBs; Mytilus galloprovincialis ; Accelerated solvent extraction; GC–MS–MS; Factorial design

Use of experimental design in the optimisation of stir bar sorptive extraction followed by thermal desorption for the determination of brominated flame retardants in water samples by A. Prieto; O. Zuloaga; A. Usobiaga; N. Etxebarria; L. A. Fernández (pp. 739-748).

A method for the determination of polybrominated diphenyl ethers (PBDEs) and polybrominated biphenyls (PBBs) in water samples is proposed. The method involving stir bar sorptive extraction (SBSE) and thermal desorption followed by gas chromatography coupled with mass spectrometry was optimised using statistical design of experiments. In the first place, the influence of different polydimethylsiloxane stir bars was studied. A Plackett–Burman design was chosen to estimate the influence of five factors on the efficiency of the SBSE process: desorption time (5–10 min), desorption temperature (250–300 °C), desorption flow (50–100 mL min⁻¹), cryofocusing temperature (-130 to 40 °C) and vent pressure (0–12.8 psi). Afterwards, two central composite designs were used to find the optimal process settings that were applied to the optimisation of both desorption and extraction efficiency. In the case of the desorption parameters, long desorption times (10 min) and desorption flows lower than 70 mL min^-1 yielded the best signals for the majority of compounds. However, different behaviour among the analytes was observed for the vent pressure and we decided to fix it at an intermediate value (7 psi). In the case of extraction parameters, the sample volume and the addition of NaCl did not have a significant effect, while the addition of methanol yielded better extraction responses. Remarkable recovery (82–106%) and repeatability (less than 18%) were attained. Furthermore, excellent regression coefficients (r ² = 0.991–0.999) and low detection limits (1.1–6.0 ng L⁻¹) were also achieved for the congeners studied. The proposed method was applied to the analyses of PBDEs and PBBs in waters from the Basque Country, Spain.

Keywords: Experimental design; Polybrominated diphenyl ethers; Polybrominated biphenyls; Stir bar sorptive extraction; Thermal desorption; Water samples

Combination of ¹³C/¹¹³Cd NMR, potentiometry, and voltammetry in characterizing the interactions between Cd and two models of the main components of soil organic matter by V. Lenoble; C. Garnier; A. Masion; F. Ziarelli; J. M. Garnier (pp. 749-757).

This work allowed the characterization of the Cd-binding sites of two compounds taken as models for exudates, the main components of soil organic matter (SOM). The studied compounds were exopolysaccharides (EPS), specifically exudates of roots (polygalacturonic acid) and of soil bacteria (Phytagel). Potentiometric acid–base titrations were performed and fitting of the obtained results indicated the presence of two main classes of acidic sites, defined by their pK _a values, for both EPS but of a different nature when comparing the two compounds. The two studied exopolysaccharides presented different acidic/basic site ratios: 0.15 for Phytagel and 0.76 for polygalacturonic acid. Spectroscopic techniques (¹³C/¹¹³Cd NMR, FTIR) distinguished different Cd surroundings for each of the studied EPS, which is in agreement with the titration results. Furthermore, these analyses indicated the presence of –COOH and –OH groups in various proportions for each exopolysaccharide, which should be linked to their reactivity towards cadmium. Cadmium titrations (voltammetric measurements) also differentiated different binding sites for each compound and allowed the determination of the strength of the Cd-binding site of the EPS. Fitting of the results of such voltammetric measurements was performed using PROSECE (Programme d’Optimisation et de Speciation Chimique dans l’Environnement), a software coupling chemical speciation calculation and binding parameter optimization. The fitting, taking into account the Cd²⁺/H⁺ competition towards exopolysaccharides, confirmed the acid-base titrations and spectroscopic analyses by revealing two classes of binding sites: (i) one defined as a strong complexant regarding its Cd²⁺–EPS association (logK = 9–10.4) and with basic functionality regarding H⁺–EPS association (pK _a = 11.3–11.7), and (ii) one defined as a weak complexant (logK = 7.1–8.2) and with acidic functionality (pK _a = 3.7–4.0). Therefore the combination of spectroscopic analyses, voltammetry, and fitting allowed the precise characterization of the binding sites of the studied exopolysaccharides, mimicking the main SOM components. Furthermore, the binding parameters obtained by fitting can be used in biogeochemical models to better define the role of key SOM compounds like exudates of roots and of soil bacteria on trace metal transport or assimilation.

Keywords: Cadmium complexation; Soil organic matter; Complexation modeling; ¹³C/¹¹³Cd NMR; Voltammetry

Multiresidue determination of chlorophenoxy acid herbicides in human urine samples by use of solid-phase extraction and capillary LC–UV detection by N. Rosales-Conrado; M. E. León-González; L. V. Pérez-Arribas; L. M. Polo-Díez (pp. 759-768).

Chlorophenoxy acid herbicides are intensively applied to get rid of unwanted plants because of their low cost and selectivity. Due to their toxicity, which depends on their chemical form, the European Community has established legal directives to restrict their use and to control their maximum residue levels in several matrices. Determination of chlorophenoxy acids—2,4-dichlorophenoxyacetic acid (2,4-D), 4-chloro-2-methylphenoxyacetic acid (MCPA), 2-(2,4-dichlorophenoxy)propanoic acid (2,4-DP), 2-(4-chloro-2-methylphenoxy)propanoic acid (MCPP), 4-(4-chloro-2-methylphenoxy)butanoic acid (MCPB) and 2-(2,4,5-trichlorophenoxy)propanoic acid (2,4,5-TP) in spiked human urine samples has been carried out by capillary LC, after solid-phase extraction on a column packed with silica C₁₈ restricted-access material. Chromatographic analysis was performed in gradient-elution mode at 25 °C, with injection of 20 μL low-organic-solvent composition herbicide solutions for focusing purposes on the head of the capillary column, and diode array detection at 232 nm. Urine samples collected during 24 h from healthy and unexposed volunteers were spiked in the concentration range 25–150 μg L⁻¹; recoveries obtained were between 66 and 100% (n = 6 for each spiked level) and RSDs (relative standard deviations) were between 1 and 5%. Detection limits in the urine samples from volunteers were between 3.5 and 6.0 μg L⁻¹. The developed methodology has allowed the clean-up and preconcentration of low volumes of untreated human urine without previous treatment, showing the effectiveness of the employed SPE sorbent for extracting the target analytes and ultimately resulting in the reduction of the sample-preparation time.

Keywords: Chlorophenoxy acid herbicides; Capillary liquid chromatography; Preconcentration and sample clean-up; Restricted-access material; Urine

Alternating current anodic stripping voltammetry in the study of cadmium complexation by a reference Suwannee river fulvic acid: a model case with strong electrode adsorption and weak binding by Anna Maria Garrigosa; Cristina Ariño; José Manuel Díaz-Cruz; Miquel Esteban (pp. 769-776).

The possibilities of anodic stripping voltammetry (ASV) using an alternating current (AC) scan in the stripping step have been checked through the study of the complexation of cadmium by Suwannee river fulvic acid (SRFA), a reference fulvic acid from the International Humic Substances Society. Because of the strong electrode adsorption of SRFA, AC mode appears to be a good approach to the study when proper selection of the phase angle is made. The goodness of AC mode in ASV has been demonstrated, and the complexation constant of 3.71 ± 0.04 determined is in good agreement with the value of the constant obtained by the reference technique of reverse pulse polarography. Some particularities of SRFA have been observed, among them its homofunctional and strongly heterogeneous behaviour in cadmium complexation and the impossibility of avoiding electrode adsorption problems in ASV measurements at very low metal concentrations. Figure DP anodic stripping and AC anodic stripping voltammograms at −12° and −65° during the titration of a 10⁻⁷ mol L⁻¹ Cd(II) solution with SRFA at pH 7.5 in 0.05 L⁻¹ Tris

Keywords: Phase-sensitive alternating current techniques; Anodic stripping voltammetry; Complex formation constants; Cadmium; Electrode adsorption; Swannee river fulvic acid

Regular variations in organic matrix composition of small yellow croaker (Pseudociaena polyactis) otoliths: an in situ Raman microspectroscopy and mapping study by Fenfen Zhang; Weiying Cai; Zhenrong Sun; Jing Zhang (pp. 777-782).

The stonelike otoliths from the ears of fish consist of calcium carbonate crystallites embedded in an organic matrix framework. The organic matrix has long been known to play a pivotal role in the biomineralization of otoliths, and different methods have been used to conduct investigations on it. A new sensitive method for the in situ study of the regular variations in the organic matrix composition of serial small yellow croaker otoliths by Raman microspectroscopy and mapping is described. The major collagen bands were always observed around 1,272 cm^-1 (amide III) and 1600–1690 cm^-1 (amide I), and 1443 and 2800–3100 cm^-1 (bending and stretching modes of CH groups, respectively). Aromatic amino acids, such as phenylalanine and tyrosine, were identified at 1,003 cm^-1 and at 830 and 853 cm^-1. Tryptophan was assigned at 1,555 cm^-1, and it was firstly found in otoliths. A regular calcification process in otoliths was observed in Raman spectral mapping results. Corresponding changes were clearly seen in the concentrations of the organic matrix and aragonite (CaCO₃) in otoliths.

Keywords: Otolith; Organic matrix; Aromatic amino acid; Raman microspectroscopy; Raman spectral mapping

Brassicaceae seed oil identified as illuminant in Nilotic shells from a first millennium AD Coptic church in Bawit, Egypt by Kerlijne Romanus; Wim Van Neer; Elena Marinova; Kristin Verbeke; Anja Luypaerts; Sabina Accardo; Ive Hermans; Pierre Jacobs; Dirk De Vos; Marc Waelkens (pp. 783-793).

Burned greasy deposits were found inside shells of the large Nile bivalve Chambardia rubens, excavated in an eight- to tenth- century AD church of the Coptic monastery of Bawit, Egypt, and supposedly used as oil lamps. The residues were subjected to a combination of chromatographic residue analysis techniques. The rather high concentrations of unsaturated fatty acids, as analysed by gas chromatography (GC) in the methylated extract, suggest the presence of a vegetal oil. Analysis of the stable carbon isotopes (δ ¹³C values) of the methyl esters also favoured plants over animals as the lipid source. In the search for biomarkers by GC coupled to mass spectrometry on a silylated extract, a range of diacids together with high concentrations of 13,14-dihydroxydocosanoate and 11,12-dihydroxyeicosanoate were found. These compounds are oxidation products of erucic acid and gondoic acid, which are abundantly present in seeds of Brassicaceae plants. Liquid chromatography coupled to mass spectrometry analysis showed low concentrations of unaltered triglycerides, but revealed sizeable amounts of triglycerides with at least one dihydroxylated acyl chain. The unusual preservation of dihydroxylated triglycerides and α,ω-dicarboxylic acids can be related to the dry preservation conditions. Analysis of the stereoisomers of the dihydroxylated fatty acids allows one to determine whether oxidation took place during burning of the fuel or afterwards. The results prove that the oil of rapeseed (Brassica napus L.) or radish (Raphanus sativus L.) was used as illuminant in early Islamic Egypt, and that not only ceramic lamps but also mollusk shells were used as fuel containers.

Keywords: Residue analysis; Egyptian lamp shells; HPLC-MS; GC-C-IRMS; GC-MS; Brassicaceae seed oil

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Analytical and Bioanalytical Chemistry (v.390, #2)