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Analytical and Bioanalytical Chemistry (v.388, #4)

Vapor generation for atomic spectroscopy by R. Sturgeon (pp. 733-734).

is currently Principal Research Officer and Group Leader for Chemical Metrology at the Institute for National Measurement Standards, National Research Council Canada, in Ottawa. His scientific interests lie in trace element analysis, vapor generation, instrument development, organometallic speciation and production of Certified Reference Materials with a focus on atomic and mass spectrometric detection. R. Sturgeon is a member of the Advisory Board of Analytical and Bioanalytical Chemistry.

Vapour-generation analytical chemistry: from Marsh to multimode sample-introduction system by Ian D. Brindle (pp. 735-741).

The history and state of knowledge of techniques available to analysts before the development of modern spectrometric techniques are surveyed in this paper. A variety of evaluative methods developed in the 19th century, with relatively minor improvements, remain in the repertoire of analysts even though they are at best semi-quantitative. Interferences with the vapour-generation reaction were identified early, as were the advantages and drawbacks of electrochemical vapour generation. This review attempts to present the earliest descriptions of vapour generation of elements and of the devices that have been used for their determination; phase-separation devices, in particular, are described.

Keywords: Hydride generation; Vapour generation; Interference; Arsenic; Marsh test; Gas–liquid separator

Electrochemical hydride generation as a sample-introduction technique in atomic spectrometry: fundamentals, interferences, and applications by Francisco Laborda; Eduardo Bolea; Juan R. Castillo (pp. 743-751).

Electrochemical hydride generation (EC-HG) has been proposed as a valid alternative to chemical generation as a sample-introduction technique in atomic spectrometry. In this review fundamental aspects of the technique are revised, including designs of electrolytic cells, mechanisms of the generation process, and interferences caused by the presence of different species. Special attention is paid to the role of the configuration of the cathodes and their materials on the efficiency of hydride generation and on interferences from concomitant species. An overview of the application of EC-HG to the analysis of real samples is also given.

Keywords: Electrochemical hydride generation; Atomic spectrometry; Interferences

Chemical vapor generation of noble metals for analytical spectrometry by Pawel Pohl; Bartlomiej Prusisz (pp. 753-762).

As is apparent from the literature devoted to the analytical atomic spectrometry, chemical vapor generation (CVG) of noble metals by reaction with tetrahydroborate in acidic media may enhance the introduction of these elements into different atomic spectrometric sources. Recent developments in the CVG of noble metals species by reaction with tetrahydroborate in acidic medium are surveyed. Different aspects of this novel technique are discussed, including type of instrumentation used for the reaction, separation and transport of the species, effect of chemical and physical factors, identification of the species, and the efficiency of the process. Limitations and future prospects of the CVG technique are discussed.

Keywords: Chemical vapor generation; Noble metals; Analytical spectrometry

The efficiency of chemical vapour generation of transition and noble metals by Tomáš Matoušek (pp. 763-767).

The efficiency data from individual reports on chemical vapour generation (CVG) of transition and noble metals are overviewed with respect to the ways that they were obtained. The values derived from direct measurement of analyte in the gaseous phase or obtained from comparison with other sample introduction techniques reflect well the true chemical vapour generation efficiency. The efficiencies reported this way do not exceed 30%. On the other hand, the percentage efficiency values derived from determination of analyte remaining in the waste liquid, usually in the high tens, can substantially overestimate the efficiency by neglecting the analyte retained within the system.

Keywords: Chemical vapour generation; Metals; Analytical spectrometry; Efficiency

Critical evaluation of the application of photochemical vapor generation in analytical atomic spectrometry by Yihua He; Xiandeng Hou; Chengbin Zheng; Ralph E. Sturgeon (pp. 769-774).

Chemical vapor generation (CVG) is a widely adopted sample introduction method for analytical atomic spectrometry. Nonvolatile precursors (usually ionic, metallic or organometallic species) can be transferred from the condensed phase to the gas phase, yielding the advantages of efficient matrix separation, high analyte transport efficiency, high selectivity, simple instrumentation, and ease of automation. Hydride generation enjoys the greatest popularity as a consequence of its ease of implementation, fast reaction and high yield; but photo-CVG, a newly emerging research field in analytical chemistry, may provide a powerful alternative to conventional CVG due to its simplicity, versatility and cost effectiveness. Although photocatalytic pre-reduction has been used for a number of years, the most attractive aspect of this newly emerging area is the direct generation of volatile species using photochemical reactions. Recent studies undertaken with flow through and batch reactors employing low molecular weight organic acids as photochemical agents are highlighted in this study for such systems as mercury and selenium, as well as reaction mechanisms considered for these processes. Discussion is focused on recent advances in photo-CVG, which we believe will become the subject of intensive future research initiatives.

Keywords: Vapor generation; Photochemical vapor generation; Photocatalysis; Photoreduction; Photooxidation; Photo-CVG

Hydride generation activity of arsenosugars and thioarsenicals by Rajendra Regmi; Bruce F. Milne; Jörg Feldmann (pp. 775-782).

The major arsenosugar compounds have been reported to be hydride-generation-active, however to a lesser extent in comparison with the inorganic arsenicals. We report here for the first time the identity and quantity of the volatile arsenicals generated by As-sugar-SO₃, As-sugar-SO₄, dimethylarsinoyl acetic acid and dimethylarsinoyl ethanol. Only one major volatile compound was identified for all four compounds studied: dimethylarsine. This means that the As–C bond to the longer carbon chain was cleaved during the hydride-generation process. Theoretical calculations at the RHF/6-31G(d,p) ab initio level confirm that this As–C bond is much weaker than the As–CH₃ bonds. Furthermore, it was revealed that the sulphur analogue of dimethylarsinic acid (DMAS ) is hydride-generation-active at pH 7 in contrast to dimethylarsinic acid, despite the fact that arsenic is also pentavalent. This has been substantiated by the calculation of the change in susceptibility of the arsenic towards nucleophilic attack when oxygen is replaced by sulphur. Hence, DMAS can easily be mistaken for a trivalent arsenic species.

Keywords: Arsenic; Hydride generation; Arsenosugars; Thioarsenicals; Inductively coupled plasma mass spectrometry; Cryotrapping; Fukui

Effect of additives on the chemical vapour generation of bismuthane by tetrahydroborate(III) derivatization by Alessandro D’Ulivo; Sebastiano S. T. Battistini; Emanuela Pitzalis; Roberto Zamboni; Zoltan Mester; Ralph E. Sturgeon (pp. 783-791).

The effect of mM concentrations of K₃[Fe(CN)₆], Fe(III), Mo(VI), KSCN and KMnO₄ on the generation of BiH₃ by the reaction of 0.2–10 μg ml⁻¹ Bi(III) with 0.2 M tetrahydroborate(III) at 1 M acidity (HCl or HNO₃) was investigated. Chemical vapour generation (CVG) of BiH₃ was investigated by atomic absorption spectrometry using a continuous flow reaction system (CF–CVG–AAS) and different mixing sequences and reagent reaction times. Gas chromatography–mass spectrometry (GC–MS) was employed in batch generation experiments with NaBD₄. In the absence of additives, the formation of Bi⁰ at high concentrations of Bi(III) caused rollover of calibration curves and limited the linear range to less than 1 μg ml⁻¹ Bi(III). In the presence of additives, the formation of Bi⁰ was not observed and the linear range was increased to 5 μg ml⁻¹ of Bi(III) while rollover was completely removed. GC–MS experiments indicated that the presence of additives did not affect the direct transfer of H from boron to bismuth. Experiments with CF–CVG–AAS and different mixing sequences and reagent reaction times suggest that additives act by preventing the formation of Bi⁰ through the formation of reaction intermediates which evolve towards the formation of BiH₃ at elevated Bi(III)/NaBH₄ ratios.

Keywords: Chemical vapour generation; Atomic absorption spectrometry; Gas chromatography–mass spectrometry; Bismuth; Tetrahydroborate

Arsine and selenium hydride trapping in a novel quartz device for atomic-absorption spectrometry by Jan Kratzer; Jiři Dědina (pp. 793-800).

A novel quartz device has been designed to trap arsine and selenium hydride and subsequently to volatilize the collected analyte and atomize it for atomic-absorption spectrometric detection. The device is actually the multiple microflame quartz-tube atomizer (multiatomizer) with inlet arm modified to serve as the trap and to accommodate the oxygen-delivery capillary used to combust hydrogen during the trapping step. The effect of relevant experimental conditions (trap temperature during trapping and hydrogen flow rate and trap temperature during volatilization) on collection and volatilization efficiency was investigated. Under the optimum conditions collection and volatilization efficiency for arsenic and selenium were 50 and 70%, respectively.

Keywords: Arsenic and selenium hydrides; Atomic-absorption spectrometry; Multiatomizer; Hydride-trapping optimization; Quartz surface

Determination of lead in wine by hydride generation atomic fluorescence spectrometry in the presence of hexacyanoferrate(III) by Irina B. Karadjova; Leonardo Lampugnani; Alessandro D’Ulivo; Massimo Onor; Dimiter L. Tsalev (pp. 801-807).

A rapid, accurate, and precise method is described for the determination of Pb in wine using continuous-flow hydride generation atomic fluorescence spectrometry (CF-HGAFS). Sample pretreatment consists of ten-fold dilution of wine followed by direct plumbane generation in the presence of 0.1 mol L⁻¹ HCl and 1% m/v K₃[Fe(CN)₆] with 1% m/v NaBH₄ as reducing agent. An aqueous standard calibration curve is recommended for Pb quantification in wine sample. The method provides a limit of detection and a limit of quantification of 0.3 μg L⁻¹ and 1 μg L⁻¹, respectively. The relative standard deviation varies between 2–6% (within-run) and 4–11% (between-run) at 3–30 μg L⁻¹ Pb levels in wine. Good agreement has been demonstrated between results obtained by CF-HGAFS and direct electrothermal atomic absorption spectrometry in analyses of red and white wines within the concentration range of 9.2–25.8 μg L⁻¹ Pb.

Keywords: Lead; Wine; Hydride generation atomic fluorescence spectrometry; Hexacyanoferrate (III)

Derivatization of organophosphorus nerve agent degradation products for gas chromatography with ICPMS and TOF-MS detection by Douglas D. Richardson; Joseph A. Caruso (pp. 809-823).

Separation and detection of seven V-type (venomous) and G-type (German) organophosphorus nerve agent degradation products by gas chromatography with inductively coupled plasma mass spectrometry (GC–ICPMS) is described. The nonvolatile alkyl phosphonic acid degradation products of interest included ethyl methylphosphonic acid (EMPA, VX acid), isopropyl methylphosphonic acid (IMPA, GB acid), ethyl hydrogen dimethylamidophosphate sodium salt (EDPA, GA acid), isobutyl hydrogen methylphosphonate (IBMPA, RVX acid), as well as pinacolyl methylphosphonic acid (PMPA), methylphosphonic acid (MPA), and cyclohexyl methylphosphonic acid (CMPA, GF acid). N-(tert-Butyldimethylsilyl)-N-methyltrifluroacetamide with 1% TBDMSCl was utilized to form the volatile TBDMS derivatives of the nerve agent degradation products for separation by GC. Exact mass confirmation of the formation of six of the TBDMS derivatives was obtained by GC–time of flight mass spectrometry (TOF-MS). The method developed here allowed for the separation and detection of all seven TBDMS derivatives as well as phosphate in less than ten minutes. Detection limits for the developed method were less than 5 pg with retention times and peak area precisions of less than 0.01 and 6%, respectively. This method was successfully applied to river water and soil matrices. To date this is the first work describing the analysis of chemical warfare agent (CWA) degradation products by GC–ICPMS. Figure Illustrated here are six parent organophosphorus nerve agents corresponding to the degradation products analyzed by gas chromatography with ICPMS and ToF-MS detection. The authors would like to thank Daisy-Malloy Hamburg and Kevin M. Kubachka for creating this figure

Keywords: GC; Mass spectrometry/ICP–MS; Derivatization; Chemical warfare agent degradation products

Photo-induced cold vapor generation with low molecular weight alcohol, aldehyde, or carboxylic acid for atomic fluorescence spectrometric determination of mercury by Chunfang Han; Chengbin Zheng; Jun Wang; Guanglei Cheng; Yi Lv; Xiandeng Hou (pp. 825-830).

With UV irradiation, Hg²⁺ in aqueous solution can be converted into Hg⁰ cold vapor by low molecular weight alcohols, aldehydes, or carboxylic acids, e.g., methanol, formaldehyde, acetaldehyde, glycol, 1,2-propanediol, glycerol, acetic acid, oxalic acid, or malonic acid. It was found that the presence of nano-TiO₂ more or less improved the efficiency of the photo-induced chemical/cold vapor generation (photo-CVG) with most of the organic reductants. The nano-TiO₂-enhanced photo-CVG systems can be coupled to various analytical atomic spectrometric techniques for the determination of ultratrace mercury. In this work, we evaluated the application of this method to the atomic fluorescence spectrometric (AFS) determination of mercury in cold vapor mode. Under the optimized experimental conditions, the instrumental limits of detection (based on three times the standard deviation of 11 measurements of a blank solution) were around 0.02–0.04 μg L⁻¹, with linear dynamic ranges up to 15 μg L⁻¹. The interference of transition metals and the mechanism of the photo-CVG are briefly discussed. Real sample analysis using the photo-CVG-AFS method revealed that it was promising for water and geological analysis of ultralow levels of mercury. Image of the photo-CVG instrumentation showing the photoreactor inside the water cooling unit

Keywords: Cold vapor generation; Mercury; Alcohol; Aldehyde; Carboxylic acid

A new vapor generation system for mercury species based on the UV irradiation of mercaptoethanol used in the determination of total and methyl mercury in environmental and biological samples by atomic fluorescence spectrometry by Yanmin Yin; Jianhua Qiu; Limin Yang; Qiuquan Wang (pp. 831-836).

A new vapor generation system for mercury (Hg) species based on the irradiation of mercaptoethanol (ME) with UV was developed to provide an effective sample introduction unit for atomic fluorescence spectrometry (AFS). Preliminary investigations of the mechanism of this novel vapor generation system were based on GC–MS and FT–IR studies. Under optimum conditions, the limits of determination for inorganic divalence mercury and methyl mercury were 60 and 50 pg mL⁻¹, respectively. Certified reference materials (BCR 463 tuna fish and BCR 580 estuarine sediment) were used to validate this new method, and the results agreed well with certified values. This new system provides an attractive alternative method of chemical vapor generation (CVG) of mercury species compared to other developed CVG systems (for example, the traditional KBH₄/NaOH–acid system). To our knowledge, this is the first systematic report on UV/ME-based Hg species vapor generation and the determination of total and methyl Hg in environmental and biological samples using UV/ME–AFS. Figure A new vapor generation system for mercury species using mercaptoethanol under UV irradiation was developed as an effective sample introduction unit for atomic fluorescence spectrometry

Keywords: UV-induced metal vapor generation; Mercaptoethanol; Mercury; Methyl mercury; Speciation; Trace elements; Atomic fluorescence spectrometry

Determination of total mercury and methylmercury in biological samples by photochemical vapor generation by Mariana A. Vieira; Anderson S. Ribeiro; Adilson J. Curtius; Ralph E. Sturgeon (pp. 837-847).

Cold vapor atomic absorption spectrometry (CV-AAS) based on photochemical reduction by exposure to UV radiation is described for the determination of methylmercury and total mercury in biological samples. Two approaches were investigated: (a) tissues were digested in either formic acid or tetramethylammonium hydroxide (TMAH), and total mercury was determined following reduction of both species by exposure of the solution to UV irradiation; (b) tissues were solubilized in TMAH, diluted to a final concentration of 0.125% m/v TMAH by addition of 10% v/v acetic acid and CH₃Hg⁺ was selectively quantitated, or the initial digests were diluted to 0.125% m/v TMAH by addition of deionized water, adjusted to pH 0.3 by addition of HCl and CH₃Hg⁺ was selectively quantitated. For each case, the optimum conditions for photochemical vapor generation (photo-CVG) were investigated. The photochemical reduction efficiency was estimated to be ∼95% by comparing the response with traditional SnCl₂ chemical reduction. The method was validated by analysis of several biological Certified Reference Materials, DORM-1, DORM-2, DOLT-2 and DOLT-3, using calibration against aqueous solutions of Hg²⁺; results showed good agreement with the certified values for total and methylmercury in all cases. Limits of detection of 6 ng/g for total mercury using formic acid, 8 ng/g for total mercury and 10 ng/g for methylmercury using TMAH were obtained. The proposed methodology is sensitive, simple and inexpensive, and promotes “green” chemistry. The potential for application to other sample types and analytes is evident.

Keywords: Mercury; Methylmercury; Speciation; Photochemical reduction; Vapor generation; Formic acid; Tetramethylammonium hydroxide

Ultrasound-assisted vapor generation of mercury by Anderson S. Ribeiro; Mariana A. Vieira; Scott Willie; Ralph E. Sturgeon (pp. 849-857).

Cold vapor generation arising from reduction of both Hg²⁺ and CH₃Hg⁺ occurs using ultrasonic (US) fields of sufficient density to achieve both localized heating as well as radical-based attack in solutions of formic and acetic acids and tetramethylammonium hydroxide (TMAH). A batch sonoreactor utilizing an ultrasonic probe as an energy source and a flow through system based on a US bath were optimized for this purpose. Reduction of CH₃Hg⁺ to Hg⁰ occurs only at relatively high US field density (>10 W cm⁻³ of sample solution) and is thus not observed when a conventional US bath is used for cold vapor generation. Speciation of mercury is thus possible by altering the power density during the measurement process. Thermal reduction of Hg²⁺ is efficient in formic acid and TMAH at 70 °C and occurs in the absence of the US field. Room temperature studies with the batch sonoreactor reveal a slow reduction process, producing temporally broad signals having an efficiency of approximately 68% of that arising from use of a conventional SnCl₂ reduction system. Molecular species of mercury are generated at high concentrations of formic and acetic acid. Factors affecting the generation of Hg⁰ were optimized and the batch sonoreactor used for the determination of total mercury in SLRS-4 river water reference material.

Keywords: Mercury; Methylmercury; Ultrasound; Cold vapor generation

Proposed reaction mechanisms for selenium UV photolysis vapor generation by computational methods by Tait Takatani; Neil Fitzgerald; John Morrison Galbraith (pp. 859-862).

The production of volatile analyte species by UV photolysis in the presence of low-molecular-weight organic acids as an alternative to chemical vapor generation has been of recent interest. The mechanism of this process is not well understood. Proposed mechanisms often involve photolytic cleavage of the organic acid as the initial step. Evidence suggests that this may not be the dominant route for UV photolysis vapor generation. In this work computational methods were applied to determine a possible alternative mechanism in the absence of free-radical production. The proposed mechanism specifically focused on selenium vapor generation. An energetically favored mechanism was found for UV photolysis of inorganic selenium in the presence of formic and acetic acids which is consistent with previously reported experimental results.

Keywords: Selenium; UV photolysis; Vapor generation; Reaction mechanisms; Computational methods

Determination of lead in sediments and sewage sludge by on-line hydride-generation axial-view inductively-coupled plasma optical-emission spectrometry using slurry sampling by Eder José dos Santos; Amanda Beatriz Herrmann; Vera Lúcia Azzolin Frescura; Bernhard Welz; Adilson José Curtius (pp. 863-868).

Among the “traditional” hydride-forming elements, lead is probably the most difficult, and its determination in this form has rarely been reported in the literature. In this paper a simple and rapid method, axial-view inductively-coupled plasma optical-emission spectrometry using on-line hydride generation (HG–ICP–OES) from samples prepared as slurry, is proposed for determination of lead in environmental samples. The samples (20–50 mg, particle size ≤120 μm) were treated with 1 mL aqua regia in a 40-kHz ultrasonic bath for 60 min. The slurry was diluted to a final volume of 50 mL with a 10% m/v solution of (NH₄)₂S₂O₈. The concentrations of NaBH₄, tartaric acid, and (NH₄)₂S₂O₈, used for on-line plumbane generation were optimized by means of a complete factorial analysis applied to an aqueous standard solution and to the slurry of a sediment certified reference material (CRM). External calibration against aqueous standards in the concentration range 10–100 μg L⁻¹ was used for analysis of six CRM—three marine sediments, one river sediment, and two sewage sludges. Analysis of the filtered slurry showed that Pb was only partially extracted into the liquid phase. Several major concomitants tested did not affect the Pb signal. The detection limit (3s, n = 10) for 20 mg sample in a final volume of 50 mL was 5.0 μg g⁻¹. Tin was the only other hydride-forming analyte that could be determined satisfactorily with Pb; for tin the detection limit was 1.0 μg g⁻¹. The values obtained for Pb and Sn were not significantly different from the certified concentrations, according to the t-test at the 95% confidence level. Nine river sediments collected locally were also analyzed and the concentrations were in agreement with results obtained after total digestion.

Keywords: Pb; ICP–OES; Slurry sampling; Hydride generation; Sludge and sediments

Imran Ali, Hassan Y. Aboul-Enein: Instrumental methods in metal ion speciation by R. Cornelis (pp. 869-870).

An on-line post-column detection system for the detection of reactive-oxygen-species-producing compounds and antioxidants in mixtures by Jeroen Kool; Sebastiaan M. Van Liempd; Stefan Harmsen; Tim Schenk; Hubertus Irth; Jan N. M. Commandeur; Nico P. E. Vermeulen (pp. 871-879).

Reactive oxygen species (ROS) can damage proteins, cause lipid peroxidation, and react with DNA, ultimately resulting in harmful effects. Antioxidants constitute one of the defense systems used to neutralize pro-oxidants. Since pro-oxidants and antioxidants are found ubiquitously in nature, pro-and antioxidant effects of individual compounds and of mixtures receive much attention in scientific research. A major bottleneck in these studies, however, is the identification of the individual pro-oxidants and antioxidants in mixtures. Here, we describe the development and validation of an on-line post-column biochemical detection system for ROS-producing compounds and antioxidants in mixtures. Inclusion of cytochrome P450s and cytochrome P450 reductase also permitted the screening of compounds that need bioactivation to exert their ROS-producing properties. This pro-oxidant and antioxidant detection system was integrated on-line with gradient HPLC. The resulting high-resolution screening technology was able to separate mixtures of ROS-producing compounds and antioxidants, allowing each species to be characterized rapidly and sensitively.

Keywords: Pro-oxidant; Antioxidant; ROS; Bioactivation; On-line; Biochemical detection

Comparison of GC–MS and LC–MS methods for the analysis of antioxidant phenolic acids in herbs by Maarit Kivilompolo; Vít Obůrka; Tuulia Hyötyläinen (pp. 881-887).

Two methods were developed for the quantitative analysis of phenolic acids in herb extracts. The methods were based on liquid chromatography–time-of-flight mass spectrometry (LC–TOFMS) and gas chromatography–mass spectrometry (GC–MS). The methods were compared in terms of their linearity, repeatability, selectivity, sensitivity and the speed of the analysis. The sensitivity was good for both methods, with limits of detection of <80 ng/ml for most of the compounds. The relative standard deviations (RSD) of the peak areas were on average 7.2% for the LC–TOFMS method and 1.4% for the GC–MS method. Both methods were found to be suitable for the determination of the target analytes, although GC–MS was better suited to the quantitative determination of compounds present at low concentrations.

Keywords: Liquid chromatography; Gas chromatography; Lamiaceae; Phenolic acids; Mass spectrometry

Dicationic ionic liquid stationary phase for GC-MS analysis of volatile compounds in herbal plants by Meiling Qi; Daniel W. Armstrong (pp. 889-899).

The seeming “dual nature” of ionic liquids (ILs) for separating both apolar and polar compounds suggests that ILs may have a great potential for complex samples like essential oils from herbal plants that contain a great variety of compounds. In the present work, a geminal dicationic IL, 1,9-di(3-vinylimidazolium)nonane bis[(trifluoromethyl)sulfonyl]imidate, was investigated for this purpose. To find the best way to achieve satisfactory separations simultaneously for the compounds in essential oils, the dicationic IL was used as the stationary phase for capillary gas chromatography (GC) in two ways, either in its pure state or as a mixed stationary phase with monocationic ILs and a polysiloxane diluent. Interestingly, it was found that the mixed stationary phase exhibited a much better selectivity for polar and nonpolar compounds than either the dicationic IL or the polysiloxane, suggesting that a kind of synergistic effect occurred when these stationary phases were combined in the way described. A comparison with two commercial stationary phases (polar and nonpolar) indicated that this novel mixed stationary phase behaved in a way closer to a polar stationary phase in terms of selectivity and elution order. The present work demonstrates that the mixed stationary phase is efficient and selective and can be an alternative choice for the GC analysis of samples of complex composition. Figure Divinyldiimidazolium-based ionic liquid stationary phase

Keywords: Dicationic ionic liquids; Essential oils; Gas chromatography–mass spectrometry

Detection of antinuclear antibodies by a colloidal gold modified optical fiber: comparison with ELISA by Ning-Sheng Lai; Chun-Chien Wang; Hui-Ling Chiang; Lai-Kwan Chau (pp. 901-907).

A fiberoptic evanescent-wave sensor has been developed for the measurement of antinuclear antibodies in sera from patients and healthy individuals. The sensor was constructed on the basis of modification of the unclad portion of an optical fiber with self-assembled gold colloids, where the colloidal gold surface was further functionalized with extractable nuclear antigens. Results show that detection of antinuclear antibodies by this sensor agrees quantitatively with the clinically accepted enzyme-linked immunosorbent assay (ELISA) method. This sensing platform has the following advantages: label-free and real-time detection capability, simple to construct and use, highly sensitive, and does not require a secondary antibody. The sensitivity of this platform is at least an order of magnitude higher than that of the ELISA method and thus may lead to a new direction in recognition of immune response. Biomolecular binding of antinuclear antibodies (ANA) with extractable nuclear antigens (ENA)-functionalized gold nanoparticles results in a change of surface plasmon absorption. When light propagates in an optical fiber by multiple total internal reflection, such a change in signal can be significantly enhanced.

Keywords: Antinuclear antibodies; Fiberoptic biosensor; Localized surface plasmon resonance; Gold nanoparticles; Enzyme-linked immunosorbent assay

Determination of ¹³C isotopic enrichment of valine and threonine by GC–C–IRMS after formation of the N(O,S)-ethoxycarbonyl ethyl ester derivatives of the amino acids by Jean-Philippe Godin; Magali Faure; Denis Breuille; Gérard Hopfgartner; Laurent-Bernard Fay (pp. 909-918).

We describe a new method of assessing, in a single run, ¹³C isotopic enrichment of both Val and Thr by gas chromatography–combustion–isotope-ratio mass spectrometry (GC–C–IRMS). This method characterised by a rapid one-step derivatisation procedure performed at room temperature to form the N(O,S)-ethoxycarbonyl ethyl ester derivatives, and a polar column for GC. The suitability of this method for Val and Thr in in-vivo samples (mucosal hydrolysate) was demonstrated by studying protein metabolism with two tracers (¹³C-valine or ¹³C-threonine). The intra-day and inter-day repeatability were both assessed either with standards or with in-vivo samples at natural abundance and at low ¹³C isotopic enrichment. For inter-day repeatability CVs were between 0.8 and 1.5% at natural abundance and lower than 5.5% at 0.112 and 0.190 atom% enrichment for Val and Thr, respectively. Overall isotopic precision was studied for eleven standard amino acid derivatives (those of Val, Ala, Leu, Iso, Gly, Pro, Asp, Thr, Ser, Met, and Phe) and was assessed at 0.32‰. The ¹³C isotopic measurement was then extended to the other amino acids (Ala, Val, Leu, Iso, Gly, Pro, Thr, and Phe) at natural abundance for in-vivo samples. The isotopic precision was better than 0.002 atom% per amino acid (for n = 4 rats). This analytical method was finally applied to an animal study to measure Thr utilization in protein synthesis.

Keywords: N(O,S)-ethoxycarbonyl ethyl ester derivative; ¹³C-amino acid derivatives; ¹³C tracer study; GC–C–IRMS

Base sequence- and T _m-dependent DNA oligomer separation by open tubular capillary columns carrying complementary DNA oligomers as probes by Kamakshaiah Charyulu Devarayapalli; Seung Pil Pack; Nagendra Kumar Kamisetty; Mitsuru Nonogawa; Seiya Watanabe; Tsutomu Kodaki; Keisuke Makino (pp. 919-928).

DNA chips prepared on a flat glass surface have unavoidable drawbacks when used for quantitative analysis. In an attempt to overcome this problem, we constructed an HPLC-type system suitable for quantitative analysis that enables base sequence- and T _m-dependent DNA oligomer separation in a flow system. A small open tubular capillary column (300-mm × 100-μm I.D.) was used. The DNA oligomers used as probes had an amino group at the 5′-end and were immobilized on the inner silica surface of the capillary column which had been sequentially treated with 3-aminopropyltriethoxysilane, butyltrimethoxysilane, and disuccinimidylglutarate. Using the combination of probe-immobilized column placed in a column oven equipped with temperature gradient function, a nano-flow-controllable pump, a small sample-loading injector, and a capillary-fitted UV detector, we succeeded in separating complementary and non-complementary DNA oligomers in specific and quantitative modes. We also designed a temperature gradient strategy for efficient separation of target DNA oligomers in DNA mixture samples. Using a column carrying two different probes with similar T _m values, their complementary target DNA oligomers were also separated and detected. The developed DNA open tubular capillary column system investigated in the present study could be further improved as an alternative tool to DNA chips to be used for the quantitative analysis of DNA or mRNA samples.

Keywords: Bioanalytical methods; Chromatography; DNA-immobilized capillary column; DNA oligomer separation

A stripping chronopotentiometric (SCP) method with a gold film electrode for determining inorganic arsenic species in seawater by Jennifer Vandenhecke; Matthieu Waeles; Ricardo D. Riso; Pierre Le Corre (pp. 929-937).

An electrochemical method based on stripping chronopotentiometry (SCP) with a gold film electrode has been developed for determining arsenic in seawater. The detection limits were 0.053 ppb (0.71 nM) and 0.022 ppb (0.29 nM) for total inorganic As (As(T)) and As(III) after deposition times of 60 and 150 s, respectively. Compared to other stripping chronopotentiometric methods that use a gold macroelectrode to perform measurements of arsenic in seawater, the procedure described here exhibits better sensitivity and a fourfold shorter deposition time. Among the SCP methods, our procedure had proven its ability to analyse arsenic(III) in seawater. It therefore allows the concentrations of the various arsenic inorganic species in seawater—i.e. As(T), As(III) and As(V)—to be analysed. The proposed method is reliable, inexpensive and compact. It was successfully applied to the study of arsenic speciation along the salinity gradient of the Penzé estuary (NW France).

Keywords: Arsenic; Stripping chronopotentiometry; Inorganic species; Seawater; Estuary

Sensitive determination of nitric oxide in some rat tissues using polymer monolith microextraction coupled to high-performance liquid chromatography with fluorescence detection by Ke-Jing Huang; Min Zhang; Wan-Zhen Xie; Hua-Shan Zhang; Yu-Qi Feng; Hong Wang (pp. 939-946).

A simple, sensitive, selective, and low-cost method is proposed for rapidly determining nitric oxide (NO) in some rat tissues. Polymer monolith microextraction (PMME) using a poly(methacrylic acid–ethylene glycol dimethacrylate) (MAA-EGDMA) monolithic column was combined with derivatization of NO using 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza-s-indacene (TMDABODIPY), and this was used to analyze the derivatives of NO by high-performance liquid chromatography (HPLC) with fluorescence detection at λ _ex/λ _em = 498/507 nm. The baseline separation of TMDABODIPY and its NO derivative is performed under simple conditions in which a C₁₈ column is used and eluted with 50 mmol L⁻¹ ethanolamine and methanol. The conditions for the extraction of NO derivatives were optimized. The limit of detection of NO was 2 × 10⁻¹² mol L⁻¹ (S/N = 3). The linearity range of the method was 9 × 10⁻¹¹−4.5 × 10⁻⁸ mol L⁻¹. The interday and intraday relative standard deviations were less than 5%. The proposed method was successfully applied to the determination of NO levels in some rat tissue samples including heart, kidney, and liver with recoveries varying from 87.1 to 95.2%.

Keywords: Poly(methacrylic acid–ethylene glycol dimethacrylate) monolith microextraction; Nitric oxide; Derivatization; 1,3,5,7-Tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza-s-indacene (TMDABODIPY); High-performance liquid chromatography (HPLC)

The use of vetiver for remediation of heavy metal soil contamination by Riccarda Antiochia; Luigi Campanella; Paola Ghezzi; K. Movassaghi (pp. 947-956).

The use of Vetiveria zizanioides (vetiver) was studied to evaluate its efficiency for the remediation of soils contaminated by heavy metals. Vetiver plants were tested for Cr, Cu, Pb and Zn. Phytoextraction and bioremediation experiments were carried out by irrigating the vetiver plants and the dry plants with solutions containing suitable amounts of Cr, Cu, Pd and Zn. The concentrations of the heavy metals were determined in both experiments in shoot and root parts of vetiver plants using inductively coupled plasma atomic emission spectroscopy after a mineralization step. Phytoextraction experiments showed a poor efficiency of vetiver for Cr and Cu uptake (both less than 0.1% in shoots and roots after 30 days), but a quite high capability of Pb and Zn uptake (0.4% in shoots and 1% in roots for Pb and 1% both in shoots and in roots for Zn, after 30 days). For these reasons the vetiver plant can be considered a quite good “hyperaccumulator” only for Pb and Zn. As for bioremediation experiments, the vetiver plant showed heavy metal uptake values significantly lower than those obtained with other biological substrates. Figure Vetiver plant

Keywords: Phytoremediation; Vetiver; Chromium; Copper; Lead; Zinc

Optimization of analytical conditions and validation of a fluorescence method for the determination of sulfadiazine in milk by R. Díez; L. Sarabia; M. C. Ortiz (pp. 957-968).

This paper describes optimization and validation of a method for sulfadiazine determination in milk samples based on sulfadiazine derivatization with fluorescamine followed by excitation–emission (fluorescence) measurement. For both the optimization and the validation, a comparison between zero-order and first-order signals has been made, showing the advantages of using first-order signals. In the optimization the effects of the temperature of the derivatization reaction, the amount of fluorescamine and the derivatization time on the instrumental signal (maximum intensity or the net analyte signal) are studied by a factorial experimental design, with the optimal values of these factors which give the highest signal being 22 °C for the reaction temperature, 50 μl fluorescamine and 20 min of derivatization time. The validation of the method under the optimal experimental conditions shows that the analytical method is fit-for-purpose, with values of the capability of detection (CCβ) of 4.3 μg l⁻¹ at a sulfadiazine concentration of zero and with probabilities of a false positive and a false negative of 5%. Around the permitted limit (established for the sulfonamides at 100 μg l⁻¹), CCβ is 112 μg l⁻¹. The precision, as the intermediate reproducibility, was established as 1.2 and 3.3 μg l⁻¹ around 0 and 100 μg l⁻¹, respectively. In the application to milk samples spiked with sulfadiazine a mean recovery of around 90% was obtained with a standard deviation of about 8% (14 samples of different concentrations).

Keywords: Optimization; Sulfadiazine; Fluorescence; Fluorescamine; Decision 2002/657/EC; Validation

Purification of denatured bovine serum albumin coated CdTe quantum dots for sensitive detection of silver(I) ions by Jian-Hao Wang; Hai-Qiao Wang; Hai-Li Zhang; Xiu-Qing Li; Xiao-Feng Hua; Yuan-Cheng Cao; Zhen-Li Huang; Yuan-Di Zhao (pp. 969-974).

CdTe quantum dots (QDs) were synthesized in aqueous solution with 3-mercaptopropionic acid as the stabilizer. Chemically reduced bovine serum albumin (BSA) was used to modify the surface of the QDs. Experimental results showed that the denatured BSA (dBSA) could be effectively conjugated to the surface of CdTe QDs. Column chromatography was used to purify the conjugates and determine the optimal ratio of dBSA to QDs. Further experimental results showed that the conjugation of QDs by dBSA efficiently improved the photoluminescence quantum yield, the chemical stability of QDs and their stability against photobleaching. A facile and sensitive method for determination of silver(I) ions was proposed based on the fluorescence quenching of the dBSA–QDs. Under the optimal conditions, the relative fluorescence intensity decreased linearly with the concentration of the silver(I) ions in the range 0.08–10.66 μM. The detection limit was 0.01 μM. This study provides a new method for the detection of metal cations. Figure In this work, denatured BSA was used to modify the surface of CdTe QDs by a simple and rapid method. And the conjugates of dBSA-QDs were purified by column of Sephadex G-100. After the purification of the conjugates, the sensitivity was greatly increased as silver (I) ions probe.

Keywords: Quantum dots; Denatured bovine serum albumin; Silver(I) ions; Fluorescent probe; Detection

Determination of tributyltin (TBT) in marine sediment using pressurised liquid extraction–gas chromatography–isotope dilution mass spectrometry (PLE–GC–IDMS) with a hexane–tropolone mixture by Piotr Konieczka; Berit Sejerøe-Olsen; Thomas P. J. Linsinger; Heinz Schimmel (pp. 975-978).

Extraction conditions for the determination of tributyltin (TBT) in sediment samples have been developed further. The analytical procedure is based on spiking with isotopically labelled analyte, pressurised liquid extraction (PLE) with a hexane/tropolone mixture, Grignard derivatization and quantification by GC–MS. It was applied to two unknown sediment samples as part of an intercomparison exercise of the Comité Consultatif pour la Quantité de Matière (CCQM). The detection limit was approximately 1.5 ng/g TBT as Sn, while the repeatability and intermediate precision (as the coefficient of variation) were 1.9% and 3.2%, respectively. The expanded uncertainty was 6.2% (coverage factor k = 2), and the accuracy was confirmed by measurement of a certified reference material.

Keywords: Tributyltin; Pressurised liquid extraction (PLE); Isotope dilution; Gas chromatography–mass spectrometry; Uncertainty budget

Several concerns about the primer design in the universal molecular beacon real-time PCR assay and its application in HBV DNA detection by Xiaomin Li; Yong Huang; Chen Song; Meiping Zhao; Yuanzong Li (pp. 979-985).

A universal hepatitis B virus (HBV) DNA detection kit is appealing for the worldwide diagnosis and monitoring of the treatment of different mutant types of hepatitis B virus. A sensitive and reproducible real-time PCR assay based on the universal molecular beacon (U-MB) technique was developed for the detection of HBV DNA in serum. The U-MB probe used in the assay has no interaction with the HBV DNA sequence. The U-MB technique not only reduced the cost of HBV detection but also had the potential for the development of a universal detection kit for different mutant HBV types and other DNA systems. To demonstrate its clinical utility, 90 serum samples were analyzed using the U-MB real-time PCR method. In the experiments we found that several crucial factors needed to be considered in the primer design, such as the avoidance of formation of severe primer–dimer and primer self-hairpin structure. With the optimized primer sets, satisfactory results were obtained for all the tested samples. We concluded that this assay would be an excellent candidate for a universal HBV DNA detection method. Principle of the U-MB real-time PCR method for HBV DNAdetection

Keywords: Universal molecular beacon (U-MB); Real-time PCR; HBV DNA; Primer design; Clinical analysis

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Analytical and Bioanalytical Chemistry (v.388, #4)