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Analytical and Bioanalytical Chemistry (v.382, #7)

Robert de Levie: Advanced Excel for Scientific Data Analysis by Michael Kumpf (pp. 1445-1446).

E. Heftmann: Chromatography, 6th edition. Fundamentals and applications of chromatography and related differential migration methods. Part A: Fundamentals and techniques by Catherine Rimmer (pp. 1447-1448).

Changing hats....becoming a supervisor or manager by John Fetzer (pp. 1449-1450).

Monitoring enzymatic conversions by mass spectrometry: a critical review by André Liesener; Uwe Karst (pp. 1451-1464).

This review highlights recent advances in the application of electrospray ionisation and matrix-assisted laser desorption/ionisation mass spectrometry (MS) to study enzymatic reactions. Several assay schemes for different fields of application are presented. The employment of MS as a means of detection in pre-steady-state kinetic studies by rapid-mixing direct analysis and rapid-mixing quench flow techniques is discussed. Several steady-state kinetic studies of a broad range of different enzymatic systems are presented as well as enzyme inhibition studies for various target enzymes. As a promising new development multiplex assays, which monitor the conversion of several substrates simultaneously in one experiment, are described. This assay type has been used for competition studies, enzymatic activity screenings and for diagnostic purposes in clinical chemistry. Generally, it can be concluded that mass spectrometry offers an intriguing alternative as detection methodology in enzymatic bioassays. Its applicability for the monitoring the conversion of naturally occurring substrates and its overall versatility make MS an especially promising tool for the study of enzyme-catalysed processes.

Keywords: Electrospray ionisation; Matrix-assisted laser desorption/ionisation; Mass spectrometry; Enzymatic bioassays; Enzyme inhibition; Multiplex assay

Contact-angle, ellipsometric, and spin-diffusion solid-state nuclear magnetic resonance spectroscopic investigations of copolymeric stationary phases immobilized on SiO₂ surfaces by Christoph Meyer; Stefan Busche; Norbert Welsch; Jürgen Wegmann; Günter Gauglitz; Klaus Albert (pp. 1465-1471).

SiO₂ surfaces—silica gel particles and silica wafers—were modified by covalently immobilizing three poly(ethylene-co-acrylic acid) copolymers, (−CH₂CH₂−)_x[CH₂CH/(CO₂H)−]_y, with different chain lengths and mass fractions of acrylic acid. ¹³C solid-state NMR spectroscopy on the modified silica gel particles revealed both mobile gauche and rigid trans aligned alkyl chains in the copolymers. For copolymers attached to silica wafers via a 3-aminopropyltriethoxysilane spacer molecule, ellipsometric measurements revealed a mean value of the layer thickness distribution of 6.5 and 4.3 nm, respectively, for the more acidic and the shorter copolymers with mobile alkyl chains mostly in the gauche conformation. For the longest and least acidic copolymer with more rigid trans ordered alkyl chains, however, a mean phase thickness of 10.6 nm was found. When this copolymer was immobilized via a 3-glycidoxypropyltrimethoxysilane spacer molecule we measured a mean layer thickness of 9.9 nm. A model of the surface morphology of this immobilization strategy was derived using spin-diffusion ¹³C NMR measurements on the corresponding modified silica. It was thereby proven that the trans and gauche-aligned alkyl chains occur in distinct domains of certain sizes on the silica surface. The surface polarity of all modified silica wafers was also investigated by measurement of contact-angle.

Keywords: Poly(ethylene-co-acrylic acid) copolymers; Spin-diffusion solid-state nuclear magnetic resonance spectroscopy; Ellipsometry; Contact-angle measurements

Determination of reactive oxygen species in single human erythrocytes using microfluidic chip electrophoresis by Yue Sun; Xue-Feng Yin; Yun-Yang Ling; Zhao-Lun Fang (pp. 1472-1476).

Reactive oxygen species (ROS) are known to not only mediate the damage of cellular constituents but also to regulate cellular signaling. Analysis of ROS is essential if we wish to understand the mechanisms of cellular alterations. In this paper, a microfluidic chip-based approach to the determination of ROS in single erythrocyte was developed by using a simple crossed-channel glass chip with integrated operational functions, including cell sampling, single cell loading, docking, lysing, and capillary electrophoretic (CE) separation with laser-induced fluorescence (LIF) detection. Non-fluorescent dihydrorhodamine 123 (DHR 123), which can be oxidized intracellularly by ROS to the fluorescent rhodamine 123 (Rh 123), was used as the fluorogenic reagent. The effect of pH on the migration time of Rh 123 and detection sensitivity was discussed. The present method minimized dilution of intracellular ROS during reaction with DHR 123 and determination. As a result, an extremely low detection limit of 0.8 amol has been achieved. The time required for complete analysis of one human erythrocyte was less than 3 min. A migration time precision of 4.1% RSD was obtained for six consecutively-injected cells. Upon stimulation with 4 mmol/l H₂O₂ for 10 min, the intracellular ROS concentration was found to increase on average by about a factor of 8.4.

Keywords: Single-cell analysis; Microfluidic chip-based electrophoresis; Laser-induced fluorescence; Reactive oxygen species; Erythrocyte

Specific molecule localization in microchannel laminar flow and its application for non-immobilized-probe analysis by Kenichi Yamashita; Daisuke Ogura; Yoshiko Yamaguchi; Masaya Miyazaki; Maria Portia Briones; Hiroyuki Nakamura; Hideaki Maeda (pp. 1477-1483).

Microfluidic systems enable superior control of fluidics. We have developed a novel size-separation method utilizing secondary flow within a microchannel. Using confocal fluorescence microscopy and computer simulation, we confirmed that separation occurred as a result of specific molecular localization in the curving part of the microchannel. Maximum separation efficiency was achieved by optimizing microchannel design and flow rate for individual separation targets. In addition, more effective separation was achieved by use of plural microchannel curves. This method was used for sequence-selective DNA sensing. Double-stranded DNA formed by hybridization between target DNA and a complementary probe had different elution profiles from those of the single-stranded non-complementary sequence. Moreover, the response depends on the length of the DNA molecules. This method does not require immobilization of either probe or target DNA, because all reactions occurred in the solution phase. Such features may reduce experimental error and the difference between data from different operators.

Keywords: Microreactor; Laminar flow; μ-TAS; Lab on a chip; Microfluidic; DNA sensing

Determination of oxaliplatin in human plasma and plasma ultrafiltrate by graphite-furnace atomic-absorption spectrometry by E. E. M. Brouwers; M. M. Tibben; M. Joerger; O. van Tellingen; H. Rosing; J. H. M. Schellens; J. H. Beijnen (pp. 1484-1490).

A method for sensitive determination of the anti-cancer agent oxaliplatin in human plasma and human plasma ultrafiltrate (pUF) is presented. The method is based on the quantification of platinum by graphite-furnace atomic-absorption spectrometry, with Zeeman correction and an atomisation temperature of 2,700°C. Sample pretreatment involves dilution of the samples with a solution containing 0.15 mol L⁻¹ NaCl and 0.20 mol L⁻¹ HCl in water. Validation was performed in accordance with the most recent FDA guidelines for bioanalytical method validation. All results were within requirements. The validated ranges of quantification were 0.10–400 μmol L⁻¹ for human pUF and 0.50–400 μmol L⁻¹ for plasma. The assay is now successfully used to support pharmacokinetic studies of cancer patients treated with oxaliplatin.

Keywords: Oxaliplatin; GF-AAS; Quantitative; Validation; Platinum; Anti-cancer drugs

Enzyme-catalyzed amplified immunoassay for the detection of Toxoplasma gondii-specific IgG using Faradaic impedance spectroscopy, CV and QCM by Yanjun Ding; Hua Wang; Guoli Shen; Ruqin Yu (pp. 1491-1499).

A highly sensitive electrochemical immunoassay for Toxoplasma gondii-specific IgG (Tg-IgG) in human serum has been developed that is based on an enzyme-catalyzed amplification due to the formation of an insoluble precipitate on the surface of a quartz crystal microbalance (QCM). T. gondii antigen (TgAg) was immobilized on the surface of a gold electrode in order to bind Tg-IgG, and this was followed by the addition of anti-Tg-IgG horseradish peroxidase conjugate (anti-Tg-IgG-HRP). Subsequent exposure to 3,3′-diaminobenzidine (DAB) led to the enzymatically-catalyzed amplified deposition of the oxidation products on the QCM surface in the presence of H₂O₂. The transduction methods electrochemical Faradaic impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to assay the resistance to electron transfer at the conductive support upon accumulation of the insoluble products. The precipitation process was monitored in real time by QCM. The assay conditions, including the concentration of immobilized TgAg and the dosage of anti-Tg-IgG-HRP conjugate, were optimized. It was found that the amount of precipitate that accumulated on the conductive QCM surface was determined by the concentration of the target analyte Tg-IgG and the time permitted for biocatalyzed precipitation. The technique was shown to give a linear electron transfer resistance response (as measured by EIS) for Tg-IgG dilutions ranging between 1:8000 and 1:200, and a detection limit of 1:9600 dilution.

Keywords: Toxoplasma gondii-specific IgG; Amplification strategy; Faradaic impedance spectroscopy; Cyclic voltammetry; Quartz crystal microbalance

Ultra-trace analysis of platinum in human tissue samples by Elisabeth Rudolph; Stephan Hann; Gerhard Stingeder; Christian Reiter (pp. 1500-1506).

Background levels of platinum were determined in human autopsy tissues taken from five individuals. The investigated specimens were lung, liver and kidney. Sample preparation involved microwave digestion followed by an open vessel treatment. Inductively-coupled plasma sector field mass spectrometry (ICP-SFMS) was applied in combination with an ultrasonic nebulization/membrane desolvation system for sample introduction. Isotope dilution analysis was employed for accurate quantification of platinum. Excellent procedural detection limits (3 s validation) of 20, 20 and 34 pg g⁻¹ dry weight were obtained for lung, liver and kidney tissue, respectively. Due to the lack of appropriate biological reference material, road dust (BCR-723) was used for method validation. Platinum levels ranging between 0.03 and 1.42 ng g⁻¹ were determined in the investigated samples. The platinum concentrations observed in human lung tissue may reflect the increasing atmospheric background levels of platinum originating from car catalysts. The presence of platinum in kidney and liver tissue samples clearly indicates the bioavailability of the element.

Keywords: Platinum; Inductively-coupled plasma sector field mass spectrometry; Autopsy tissue; Lung; Liver; Kidney

Determination of traces of bismuth by quenching of solid-substrate room-temperature phosphorescence from morin-labeled silicon dioxide nano-particles by Jia-ming Liu; Shi-Rong Hu; Xiu-mei He; Xue-lin Li; Feng-ping Zhan; Li-qing Zeng; Long-Di Li; Guo-hui Zhu; Xiao-mei Huang (pp. 1507-1512).

Silicon dioxide nano-particles, diameter 50 nm, containing morin (morin–SiO₂) have been synthesized by the sol–gel method. They emit strong and stable room-temperature phosphorescence (SS-RTP) on filter paper as substrate, and bismuth can quench the intensity of the SS-RTP. On this basis a new morin–SiO₂ solid-substrate room-temperature phosphorescence-quenching method has been established for determination of traces of bismuth. Reduction of phosphorescence intensity (ΔI_p) is directly proportional to the concentration of bismuth in the working range 0.16–14.4 ag spot⁻¹ (sample volume 0.40 μL spot⁻¹, corresponding to the concentration range 0.40–36.0 fg mL⁻¹). The regression equation of the working curve is ΔI_p=14.86+5.279×[Bi³⁺] (ag spot⁻¹) (n=6, r=0.9982). The detection limit of this method is 0.026 ag spot⁻¹ (corresponding to a concentration of 6.5×10⁻¹⁷ g mL⁻¹).This sensitive, reproducible and accurate method has been used for successful analysis of real samples.

Keywords: Bismuth; Solid-substrate room-temperature phosphorescence-quenching method; Silicon dioxide nano-particle containing morin (morin–SiO₂)

Investigating the binding interaction of azur A with hyaluronic acid via spectrophotometry and its analytical application by Q. Chen; X. L. Li; Q. Liu; Q. C. Jiao; W. G. Cao; H. Wan (pp. 1513-1519).

The interaction between azur A (AA) and hyaluronic acid (HA) at AA concentrations from 3.430×10⁻⁵ to 8.575×10⁻⁵ M and sodium chloride concentrations from 0 to 0.01 M was investigated spectrophotometrically at 620 nm at temperatures from 0 to 50 °C. AA was shown to be a useful spectroscopic probe for detecting carboxyl groups in HA macromolecules. The interaction between AA and HA was temperature sensitive and little AA–HA interaction was observed at temperatures higher than 30 °C. The interaction of HA with AA was seen to be electrostatic in nature. The maximum binding number decreased with decreasing NaCl concentration, and the absorbance sensitivity decreased with increasing NaCl concentration in aqueous solution. Self-interference from the AA in the AA–HA interaction caused an overestimate of the molar mass of hyaluronic acid. An improved method was proposed to estimate the molar mass of HA, and a molar mass of 1.219×10⁶ Da was obtained with this improved method for HA.

Keywords: Glycosaminoglycan; Hyaluronic acid; Azur A; Spectroscopic probe; Molar mass; Maximum binding number

Animal glues in mixtures of natural binding media used in artistic and historic objects: identification by capillary zone electrophoresis by Sabine M. Harrison; Isabella Kaml; Vendula Prokoratova; Michael Mazanek; Ernst Kenndler (pp. 1520-1526).

Animal glues were often used in historic and artistic objects, e.g. as paint ground, as binders for pigments, or as adhesives. The sources were egg, casein, or different collagens. For restoration and conservation purposes it is important to know which kind of animal glue a museum object contains. Capillary electrophoresis can deliver such information, because it enables differentiation among the three proteinaceous glue classes according to their different amino acid patterns after hydrolysis. This work deals with the most relevant problem in practice, whether this identification is obstructed by the presence of other binders, with which they are mixed in many real samples; in particular, interference from plant gums and drying oils was investigated. Capillary electrophoresis of the hydrolysates (after reaction with 6 mol L⁻¹ HCl) was performed with an acidic background electrolyte consisting of chloroacetic acid (51.9 mmol L⁻¹) adjusted with LiOH to pH 2.26. The underivatised analytes were detected with a contactless conductivity detector. It was found that the constituents of the plant gums (monosaccharides) or drying oils (long-chain fatty acids and short-chain dicarboxylic acids) never interfered with identification of the animal glues, as shown for artificial mixtures of the different binders even at tenfold excess over the animal glue, and for egg tempera samples. The method was used to identify the filling material from a statue from the eighteenth century.

Keywords: Museum objects; Artefacts; Binder; Natural binding media; Proteinaceous binder; Animal glues; Plant gums; Drying oils; Fatty acid; Analysis

Photoisomerization kinetics of trifloxystrobin by Kaushik Banerjee; Axel Patrick Ligon; Michael Spiteller (pp. 1527-1533).

The photoisomerization kinetics of trifloxystrobin (TFS) in acetone under artificial sunlight is reported. HPLC analysis showed the TFS, a strobilurine fungicide of EE conformation, was converted into an equilibrium mixture of four isomers after illumination for 7 h. The isomers were identified as EZ, EE, ZZ, and ZE and were separated in the crystalline form by preparative HPLC and characterized by use of a variety of spectroscopic techniques. The quantum yield and reaction constants for the isomerization reactions were determined. The detailed spectral features of the individual isomers measured by UV, IR, Raman, NMR and mass spectroscopy are presented and compared. The spectra of the isomers were found to be very characteristic, with good analytical significance.

Keywords: Trifloxystrobin; Isomerization kinetics; HPLC; UV; NMR; Mass spectroscopy

Molecularly-imprinted polypyrrole-modified stainless steel frits for selective solid phase preconcentration of ochratoxin A by Jorn C. C. Yu; Svetla Krushkova; Edward P. C. Lai; Ewa Dabek-Zlotorzynska (pp. 1534-1540).

A molecularly-imprinted polymer (MIP) was prepared by electropolymerization of pyrrole (Py) onto a stainless steel frit, using ochratoxin A (OTA) as the template, in order to make a micro solid phase preconcentration (μSPP) device. The OTA template was removed with 1% triethylamine (TEA) in methanol. Compared to non-imprinted polypyrrole (PPy), the molecularly-imprinted polypyrrole (MIPPy) enhanced the selective binding of OTA. The percentage recovery improved from 0 to 40% when the OTA sample solution was acidified with 1 M HCl (1% by volume). At a flow rate of 0.2 mL/min, maximum OTA binding was reached in 6 min after a total loading of 3.2 ng OTA. Final elution of the OTA was analyzed by high performance liquid chromatography (HPLC) with fluorescence detection, using 20:80 v/v acetonitrile–ammonia buffer (NH₄Cl/NH₃, 20 mM, pH 9.2) as the mobile phase. The MIPPy-μSPP-HPLC results clearly demonstrated that the MIPPy-μSPP device afforded selective preconcentration of OTA from red wine samples, at OTA concentration levels as low as 0.05 ppb, prior to HPLC analysis.

Keywords: Electro-imprinting; Molecularly-imprinted polymer; Polypyrrole; Stainless steel frit; Micro solid phase preconcentration; Ochratoxin A

Analysis of sorption and bioavailability of different species of mercury on model soil components using XAS techniques and sensor bacteria by Anna Bernaus; Xavier Gaona; Angela Ivask; Anne Kahru; Manuel Valiente (pp. 1541-1548).

The present work studies the adsorption behaviour of mercury species on different soil components (montmorillonite, kaolinite and humic acid) spiked with CH₃HgCl and CH₃HgOH at different pH values, by using XAS techniques and bacterial mercury sensors in order to evaluate the availability of methyl mercury on soil components. The study details and discusses different aspects of the adsorption process, including sample preparation (with analysis of adsorbed methyl mercury by ICP-OES), the various adsorption conditions, and the characterization of spiked samples by XAS techniques performed at two synchrotron facilities (ESRF in Grenoble, France and HASYLAB in Hamburg, Germany), as well as bioavailability studies using mercury-specific sensor bacteria. Results show that XAS is a valuable qualitative technique that can be used to identify the bonding character of the Hg in mercury environment. The amount of methyl in mercury adsorbed to montmorillonite was pH-dependent while for all soil components studied, the bond character was not affected by pH. On the other hand, clays exhibited more ionic bonding character than humic acids did with methyl mercury. This interaction has a higher covalent character and so it is more stable for CH₃HgOH than for CH₃HgCl, due to the higher reactivity of the hydroxyl group arising from the possible formation of hydrogen bonds.The bioavailability of methyl mercury adsorbed to montmorillonite, kaolinite and humic acids was measured using recombinant luminescent sensor bacterium Escherichia coli MC1061 (pmerBR_BSluc). In case of contact exposure (suspension assays), the results showed that the bioavailability was higher than it was for exposure to particle-free extracts prepared from these suspensions. The highest bioavailability of methyl mercury was found in suspensions of montmorillonite (about 50% of the total amount), while the bioavailabilities of kaolinite and humic acids were five times lower (about 10%). The behaviour of methyl mercury in the presence of montmorillonite could be explained by the more ionic bonding character of this system, in contrast to the more covalent bonding character observed for humic acids. Thus, XAS techniques seem to provide promising tools for investigating the mechanisms behind the observed bioavailabilities of metals in various environmental matrices, an important topic in environmental toxicology.

Keywords: Methyl mercury adsorption; Bonding type; Synchrotron; XANES; Recombinant luminescent mercury sensor bacteria

Development of a PLS based method for determination of the quality of beers by use of NIR: spectral ranges and sample-introduction considerations by Fernando A. Iñón; Rafael Llario; Salvador Garrigues; Miguel de la Guardia (pp. 1549-1561).

Near infrared spectroscopy (NIR) has been used to determine important indicators of the quality of beers, for example original and real extract and alcohol content, using a partial least squares (PLS) calibration approach. A population of 43 samples, obtained commercially in Spain and including different types of beer, was used. Cluster hierarchical analysis was used to select calibration and validation data sets. Absorbance sample spectra, in transmission mode, were obtained in triplicate by using a 1-mm pathlength quartz flow cell and glass chromatography vials of 6.5 mm internal diameter. The two methods of sample introduction were compared critically, on the basis of spectral reproducibility for triplicate measurements and after careful selection of the best spectral pre-processing and the spectral range for building the PLS model, to obtain the best predictive capability. For each mode of sample introduction two calibration sets were assayed, one based on the use of 15 samples and a second extended based on use of 30 samples, thus leaving 28 and 13 samples, respectively, for validation. The best results were obtained for 1 mm flow cell measurements. For this method original zero-order spectra data in the ranges 2220–2221 and 2250–2350 nm were chosen. For the real extract, original extract, and alcohol d_x-y and s_x-y values of −0.04 and 0.07% w/w, −0.01 and 0.13% w/w, and −0.01 and 0.1% v/v, respectively, were obtained. The maximum errors in the prediction of any of these three indicators for a new sample were 2.2, 1.2, and 1.9%, respectively. This method compares favorably with the automatic reference method in terms of speed, reagent consumed, and waste generated.

Keywords: Determination; Original and real extract; Alcohol content; Beers; Hierarchical cluster analysis; PLS

Uncertainty in aflatoxin B₁ analysis using information from proficiency tests by Alicia Maroto; Ricard Boqué; Jordi Riu; Itziar Ruisánchez; Marta Òdena (pp. 1562-1566).

We describe how to calculate uncertainty in the determination of aflatoxin B₁ in nuts and maize using an HPLC method with prederivatisation with trifluoroacetic acid and fluorescence detection. The uncertainty is easily calculated using the information obtained from the participation in several proficiency tests. All the sources of uncertainty are grouped in two terms: (1) matrix variability, intermediate precision and sample heterogeneity, and (2) method concordance. This methodology has the advantage that no extra work needs to be done because all the information to calculate uncertainty comes from proficiency tests. The uncertainty values were calculated using samples whose concentration ranged between 2 and 20 μg L⁻¹. The relative standard uncertainty computed for aflatoxin B₁ was 16.3%.

Keywords: Measurement uncertainty; Proficiency tests; Aflatoxin analysis

Determination of platinum-group metals and lead in vegetable environmental bio-monitors by voltammetric and spectroscopic techniques: critical comparison by Clinio Locatelli; Dora Melucci; Giancarlo Torsi (pp. 1567-1573).

This paper reports voltammetric sequential determination of Pt(II), Pd(II), and Rh(III), by square-wave adsorption stripping voltammetry (SWAdSV), and Pb(II), by square-wave anodic stripping voltammetry (SWASV), in vegetable environmental matrices. Analytical procedures were verified by the analysis of the standard reference materials: Olive Leaves BCR-CRM 062 and Tomato Leaves NIST-SRM 1573a. Precision and accuracy, expressed as relative standard deviation and relative error, respectively, were always less than 6% and the limits of detection (LOD) for each element were below 0.096 μg g⁻¹. Once set up on the standard reference materials, the analytical procedure was transferred and applied to laurel leaves sampled in proximity to a superhighway and in the Po river mouth area. A critical comparison with spectroscopic measurements is discussed.

Keywords: Platinum-group metals; Lead; Voltammetry; Spectroscopy; Vegetables

Pressurised solvent extraction for organotin speciation in vegetable matrices by Christophe Marcic; Gaëtane Lespes; Martine Potin-Gautier (pp. 1574-1583).

Because organotin compounds (OTC) are widely used in many fields of activity, they have become an ubiquitous environmental presence. The presence of organotins in the environment impacts upon food safety, making it important to monitor the levels of organotin pesticides in fruits and vegetables. Nevertheless, only a few studies have been published on organotin speciation in plants. The objective of the present study was to evaluate and optimise a specific procedure based on pressurised solvent extraction (PSE) that is suitable for monitoring organotin content in vegetables. In ASE, solvents are used at elevated temperatures and pressures to increase the rate and efficiency of the extraction process. The results from this procedure were compared to those from the technique usually employed, solid/liquid extraction (SLE) performed in an acidic solvent by mechanical shaking. Three extracting solutions were tested—methanol, ethyl acetate and a mixture of methanol and ethyl acetate—and the mixture was found to give the most quantitative results while preserving the speciation. French bean and lettuce leaves as well as potato tubers were used as the plant materials. These vegetables were considered because they are the vegatables consumed in the most quantities in Europe. The study focuses on trisubstituted OTCs, which are the most toxic tin species. The samples were spiked with four trisubstituted organotins: tributyltin (TBT), triphenyltin (TPhT), tricyclohexyltin (TcHexT) and trioctyltin (TOcT). The influence of the pressure and the temperature of the PSE on the quantitativity of the process and on species preservation was evaluated using the experimental design methodology. The optimised PSE allowed detection limits down to 1–2 ng (Sn) g⁻¹ to be reached. These are higher than those obtained by SLE (0.1–1 ng (Sn) g⁻¹). Although the repeatability is similar for both PSE and SLE (2–12% for triorganotin compounds), this appears to be highly time-dependent in the case of SLE. Comparison with SLE confirms that PSE is an interesting tool for vegetable analysis considering the satisfactory OTC preservation and repeatability obtained for a relatively short extraction duration (only 15 min against 2–12 h for SLE).

Keywords: Pressurised solvent extraction; Organotins; Speciation; Vegetables

Use of a stopped-flow technique for investigation and determination of thiourea and its N-methyl derivatives as inducers of the iodine–azide reaction by Jan Kurzawa; Krystyna Janowicz (pp. 1584-1589).

A stopped-flow technique has been used to investigate the behaviour of 2-thiourea, 1-methyl-2-thiourea, 1,3-dimethyl-2-thiourea, and 1,1,3,3-tetramethyl-2-thiourea in the induced iodine–azide reaction. This technique enables the progress of the reaction to be followed by monitoring the decrease in the absorbance of the iodine–starch complex at 595 nm. The effect of the concentration of the reagents on the rate of the reaction was investigated and a kinetic method for determination of the compounds is proposed. 2-Thiourea, 1-methyl-2-thiourea, and 1,3-dimethyl-2-thiourea can be determined in the range 3–75 μmol L⁻¹ and 1,1,3,3-tetramethyl-2-thiourea in the range 2–200 μmol L⁻¹.

Keywords: ThioureaN-methylthiourea; Stopped-flow; Iodine–azide reaction

Preparation of strong anion-exchange chromatographic packings based on monodisperse polymeric beads and their application in the separation of biopolymers by Bolin Gong; Long Li; Jinxia Zhu (pp. 1590-1594).

A new hydrophilic strong anion-exchange (SAX) stationary phase for HPLC has been synthesized by chemical modification of macroporous 8.0-μm monodisperse poly(glycidylmethacrylate-co-ethylenedimethacrylate) beads (P_GMA/EDMA). The stationary phase was evaluated in detail to determine its ion-exchange properties, separability, reproducibility, hydrophilicity, and the effect of column loading and pH on the separation and retention of proteins. It was found to have an ion-exchange chromatographic (IEC) retention mechanism. The highest dynamic protein loading capacity of the synthesized SAX packing for BSA was 22.6 mg g⁻¹. Five proteins were separated within 6.0 min using the synthesized SAX resin. The SAX resin was also used for rapid separation and purification of recombinant human stem cell factor (rhSCF) from a crude extract solution in only one step. The purity of the purified of rhSCF was >92.4%.

Keywords: Monodisperse poly(glycidylmethacrylate-co-ethylenedimethacrylate) resins; Strong anion-exchange chromatography; Protein separation; Recombinant human stem cell factor

A sensitive and specific HPLC-MS method for the determination of sophoridine, sophocarpine and matrine in rabbit plasma by Yong-jiang Wu; Jian-jun Chen; Yi-yu Cheng (pp. 1595-1600).

A sensitive and specific method was developed for the determination of sophoridine (SRI), sophocarpine (SC) and matrine (MT) in rabbit plasma by HPLC-MS. After an administration of Kuhuang by injection, blood samples were collected and extracted with methanol. The extract solutions were analysed by HPLC-MS method. The separation was performed on a ZORBAX Extend-C18 column using methanol/water/diethylamine (50:50:0.07, v/v/v) as mobile phase. The quinolizidine alkaloids were detected by using mass spectrometry in the SIM mode. There was a good linear relationship between peak area and concentration of analytes over the concentration range of 13.2–995.0 ng mL⁻¹ for SRI, 7.0–530.0 ng mL⁻¹ for SC and 8.8–655.0 ng mL⁻¹ for MT, respectively. The absolute recovery of this method was more than 57% for SRI, 87% for SC and 91% for MT. The accuracy of assay was more than 90%. The limits of detection (LODs) were 6.8 ng mL⁻¹ for SRI, 3.5 ng mL⁻¹ for SC and 4.2 ng mL⁻¹ for MT, respectively. The limits of quantitation (LOQs) were 13.2 ng mL⁻¹ for SRI, 7.0 ng mL⁻¹ for SC and 8.8 ng mL⁻¹ for MT, respectively. The intra-day and inter-day coefficients of variation (RSDs) were less than 10.1, 6.3 and 5.8% for SRI, SC and MT, respectively. The developed method was applied to determine the concentration–time profiles of SRI, SC and MT in rabbit plasma after injection of Kuhuang.

Keywords: Sophoridine; Sophocarpine; Matrine; High-performance liquid chromatography; Mass spectrometry; Pharmacokinetics

Simultaneous determination of DTPA, EDTA, and NTA by UV–visible spectrometry and HPLC by Pirita Laine; Rose Matilainen (pp. 1601-1609).

In this study, UV–visible spectrophotometry (UV–Vis) and high-performance liquid chromatography (HPLC) were used for simultaneous analysis of chelating agents diethylenetriamine pentaacetic acid (DTPA), ethylenediamine tetraacetic acid (EDTA), and nitrilotriacetic acid (NTA), as their metal chelates in dishwashing detergents, natural waters, and pulp mill water. The total amounts of the chelating agents in dishwashing detergents were verified by potentiometric titration with Fe(III) solution. Nickel(II) chelates were determined by UV–Vis and iron(III)chelates by HPLC and titration. Recoveries of DTPA, EDTA, and NTA from a standard mixture of analytes by UV–Vis were 107±7, 101±12 and 94±13%, respectively, and the recovery of the total amount of complexing agents was 99±4%. The limits of detection for DTPA, EDTA, and NTA were 667, 324, and 739 μmol L⁻¹, respectively. In HPLC measurements the optimized mobile phase contained 0.03 mol L⁻¹ sodium acetate, 0.002 mol L⁻¹ tetrabutylammonium bromide, and 5% methanol at pH 3.15 and the detection was by UV–Vis detection at 254 nm. All three complexing agents could be separated from each other in a simultaneous analysis in less than 5 min. The limits of detection were 0.34, 0.27, and 0.62 μmol L⁻¹ for DTPA, EDTA, and NTA, respectively. The total amounts of the analytes measured in the dishwashing detergents by the three techniques were found to be highly comparable (ANOVA: F=0.04, P=0.96). R² values were 0.99 for EDTA, 0.99 for NTA, and 0.99 for all the results when UV–Vis and HPLC determinations were compared using regression lines. The UV–Vis and HPLC methods were proved to be viable also for analyses of natural and pulp mill waters. The absence of matrix interferences was verified by the standard addition technique.

Keywords: Complexing agents; Spectrophotometry; High-performance liquid chromatography; Water; Detergent

Determination of saikosaponins a, c, and d in Bupleurum Chinese DC from different areas by capillary zone electrophoresis by Xiuli Lin; Ling Xue; Huiyun Zhang; Chenfu Zhu (pp. 1610-1615).

A fast capillary zone electrophoresis (CZE) method was developed for the determination and separation of saikosaponins a, c, and d in Chinese herbal extracts of Bupleurum Chinese DC from different areas. Detection at 214 nm with a system containing sodium borate buffer and mono-3-phenylcarbamoyl-β-CD was found to be the most suitable approach for this analysis. Saikosaponins a, c, and d could be easily determined within 8 min. The effect of the concentration of mono-3-phenylcarbamoyl-β-CD, the concentration of the running buffer and buffer pH value on the migration behavior of the saikosaponins is discussed.

Keywords: SaikosaponinsBupleurum Chinese DC; Capillary zone electrophoresis

Determination of jasmonic acid in bark extracts from Hevea brasiliensis by capillary electrophoresis with laser-induced fluorescence detection by Zhi-Li Zhang; Xin Liu; Dian-Fan Li; Ying-Tang Lu (pp. 1616-1619).

A simple and sensitive method is described for determination of jasmonic acid (JA) in plant tissues. The method is based on derivatization of JA with 5-bromomethylfluorescein (5-BMF) and separation and quantification of the resulting 5-BMF–JA derivative by capillary electrophoresis coupled to laser-induced fluorescence detection (CE–LIF). The derivatization conditions were studied in detail. Our results indicated that 5-BMF-labeled JA could be well separated from other plant hormones present in the sample by use of 20 mmol L⁻¹ borate buffer (pH 8.5). The response to JA was a linear function of concentration in the range 1 to 100 μmol L⁻¹, with a correlation of 0.9986. Our preliminary work showed that the proposed method had fairly good selectivity and sensitivity. Only small amounts of plant sample are needed to complete the analysis. This described method enables the analysis of JA in crude extracts without extra purification and enrichment procedures.

Keywords: Derivatization; Jasmonic acid; 5-Bromomethylfluorescein; Capillary electrophoresis laser induced fluorescent detection

Quantification of free and total salicylic acid in plants by solid-phase extraction and isocratic high-performance anion-exchange chromatography by Wilfried Rozhon; Elena Petutschnig; Michael Wrzaczek; Claudia Jonak (pp. 1620-1627).

Salicylic acid (SA) is an important signaling compound in plants and is involved in various defense responses. Here we report a new method for quantification of free and total soluble SA in Arabidopsis thaliana with 5-fluorosalicylic acid (5-FSA) as internal standard. The SA was isolated from leaf extracts by solid-phase extraction with phenyl-phase cartridges and selectively eluted as the cationic iron(III)-complex. Recoveries of SA and 5-FSA were equal and exceeded 90%. Free SA was subsequently released from the iron(III)-complex by addition of 2,2′-bipyridyl and high-performance anion-exchange chromatography was performed on an NH₂ column. The SA appeared as last peak with a retention time of 15 min, baseline-separated from other substances. On-line detection was performed fluorimetrically for both SA and 5-FSA at an excitation wavelength of 300 nm and an emission wavelength of 410 nm, because both substances give similar fluorescence spectra. The detection limit for SA was 5 ng g⁻¹ FW for a sample size of 100 mg. Thus the main advantages of the method are highly selective sample preparation, increased sensitivity, reduced analysis time compared with reversed-phase HPLC, and use of a novel internal standard detectable under the same conditions as SA. The techniques described are applicable to other plant materials.

Keywords: Arabidopsis5-Fluorosalicylic acid; High-performance anion-exchange chromatography; Salicylic acid; Solid-phase extraction

Optochemical sensor for determining ozone based on novel soluble indigo dyes immobilised in a highly permeable polymeric film by Marcin Alexy; Gundula Voss; Jürgen Heinze (pp. 1628-1641).

An optochemical ozone sensor is described that has been manufactured by immobilisation of novel soluble indigo derivatives in permeable transparent polymeric films of polydimethylsiloxane–polycarbonate copolymer. From a number of investigated indigo derivatives, 4,4′,7,7′-tetraalkoxyindigo 9 has been selected for optimal sensitivity and specificity of ozone detection. A linear calibration for ozone can be obtained in the range between 0.01 and 0.5 ppm. The limit of quantitation is 0.03 ppm, and the accuracy exceeds 8%. It takes about 134 s to measure the relatively low occupational exposure concentration of 0.1 ppm. A reduction of the sensor response time could be achieved through application of double-sided coated sensors instead of single-sided variants. The stability of the sensors and the effect of external parameters like relative humidity (RH), temperature and gas flow on the sensor response have been investigated. The sensor response is affected by varying the gas flow or temperature; however, humidity in the range between 0 and 90% RH does not affect sensor response. The indigo derivative 9 remained stable inside the polymeric film and no chemical reaction, crystallisation or leaching occurred during 10 months of observation. Proper choice of indicator dye and polymeric material and successful application of kinetic evaluation method for the exposure experiments determine the desired features of the sensor.

Keywords: Gas sensor; Optochemical sensor; Indigo derivatives; Ozone detection; UV–Vis spectroscopy

Transport properties and electroanalytical response characteristics of drotaverine ion-selective sensors by Sergey V. Kharitonov (pp. 1642-1651).

The construction and electroanalytical response characteristics of poly(vinyl chloride) matrix ion-selective sensors (ISSs) for drotaverine hydrochloride are described. The membranes incorporate ion-association complexes of drotaverine with tetraphenylborate, picrate, tetraiodomercurate, tetraiodobismuthate, Reinecke salt, and heteropolycompounds of Keggin structure—molybdophosphoric acid, tungstophosphoric acid, molybdosiliconic acid and tungstosiliconic acid as electroactive materials for ionometric sensor controls. These ISSs have a linear response to drotaverine hydrochloride over the range 8×10⁻⁶ to 5×10⁻² mol L⁻¹ with cationic slopes from 51 to 58 mV per concentration decade. These ISSs have a fast response time (up to 1 min), a low determination limit (down to 4.3×10⁻⁶ mol L⁻¹), good stability (3–5 weeks), and reasonable selectivity. Permeabilities and ion fluxes through a membrane were calculated for major and interfering ions. Dependences of the transport properties of the membranes on the concentrations of the ion exchanger and near-membrane solution and their electrochemical characteristics are presented. The ISSs were used for direct potentiometry and potentiometric titration (sodium tetraphenylborate) of drotaverine hydrochloride. Results with mean accuracy of 99.1±1.0% of nominal were obtained which corresponded well to data obtained by use of high-performance liquid chromatography.

Keywords: Drotaverine hydrochloride; Ion-selective electrodes; Permeability coefficient; Ion flux

Application of cause-and-effect analysis to potentiometric titration by A. Kufelnicki; S. Lis; G. Meinrath (pp. 1652-1661).

A first attempt has been made to interpret physicochemical data from potentiometric titration analysis in accordance with the complete measurement-uncertainty budget approach (bottom-up) of ISO and Eurachem. A cause-and-effect diagram is established and discussed. Titration data for arsenazo III are used as a basis for this discussion. The commercial software Superquad is used and applied within a computer-intensive resampling framework. The cause-and-effect diagram is applied to evaluation of seven protonation constants of arsenazo III in the pH range 2–10.7. The data interpretation is based on empirical probability distributions and their analysis by second-order correct confidence estimates. The evaluated data are applied in the calculation of a speciation diagram including uncertainty estimates using the probabilistic speciation software Ljungskile.

Keywords: Metrology in chemistry; Measurement uncertainty budget; Protonation constants; Speciation; Arsenazo III; Computer-intensive resampling methods

Electroanalytical study of fluvoxamine by Henri P. A. Nouws; Cristina Delerue-Matos; Aquiles A. Barros; José A. Rodrigues; Alice Santos-Silva (pp. 1662-1668).

Fluvoxamine (FVX) can be reduced at a mercury-drop electrode, with a maximum peak current intensity being obtained at a potential of −0.7 V vs. Ag/AgCl, in an aqueous electrolyte solution of pH 2. The compound was determined in a pharmaceutical product and in spiked human serum by square-wave adsorptive-stripping voltammetry (SWAdSV) after accumulation at the electrode surface, under batch conditions. Because the presence of dissolved oxygen did not interfere significantly with the analysis, it was also possible to determine FVX in the pharmaceutical product by use of a flow-injection analysis (FIA) system with SWAdSV detection. The methods developed were validated and successfully applied to the quantification of FVX in a pharmaceutical product. Recoveries between 76 and 89% were obtained in serum analysis. The FIA–SWAdSV method enabled analysis of up to 120 samples per hour at reduced cost, implying the possibility of competing with the chromatographic methods usually used for this analysis.

Keywords: Fluvoxamine; Square-wave adsorptive-stripping voltammetry; Flow-injection analysis; Electrochemical detection; Pharmaceuticals; Serum

Electrochemical behavior of a covalently modified glassy carbon electrode with aspartic acid and its use for voltammetric differentiation of dopamine and ascorbic acid by Lei Zhang; Xiangqin Lin (pp. 1669-1677).

Aspartic acid was covalently grafted on to a glassy carbon electrode (GCE) by amine cation radical formation in the electrooxidation of the amino-containing compound. X-ray photoelectron spectroscopic (XPS) measurement and cyclic voltammetric experiments proved the aspartic acid was immobilized as a monolayer on the GCE. Electron transfer to Fe(CN)₆⁴⁻ in solution of different pH was studied by cyclic voltammetry. Changes in solution pH resulted in the variation of the charge state of the terminal group; surface pK_a values were estimated on the basis of these results. Because of electrostatic interactions between the negatively charged groups on the electrode surface and dopamine (DA) and ascorbic acid (AA), the modified electrode was used for electrochemical differentiation between DA and AA. The peak current for DA at the modified electrode was greatly enhanced and that for AA was significantly reduced, which enabled determination of DA in the presence of AA. The differential pulse voltammetric (DPV) peak current was linearly dependent on DA concentration over the range 1.8×10⁻⁶–4.6×10⁻⁴ mol L⁻¹ with slope (nA μmol⁻¹ L) and intercept (nA) of 47.6 and 49.2, respectively. The detection limit (3δ) was 1.2×10⁻⁶ mol L⁻¹. The high selectivity and sensitivity for dopamine was attributed to charge discrimination and analyte accumulation. The modified electrode has been used for determination of DA in samples, in the presence of AA, with satisfactory results.

Keywords: Electrocatalytic oxidation; Monolayer; Chemically modified electrode; Aspartic acid; Dopamine

Determination of subnanomolar concentrations of cobalt by adsorptive stripping voltammetry at a bismuth film electrode by Mieczyslaw Korolczuk; Aleksandra Moroziewicz; Malgorzata Grabarczyk (pp. 1678-1682).

Procedures for trace cobalt determinations by adsorptive stripping voltammetry at in situ and ex situ plated bismuth film electrodes are presented. These exploit the enhancement of the cobalt peak obtained by using the Co(II)–dimethylglyoxime–cetyltrimethylammonium bromide–piperazine-N,N′-bis(2-ethanesulfonic acid) system. The calibration graph for an accumulation time of 120 s was linear from 2 × 10^–10 to 2 × 10^–8 mol L⁻¹. The relative standard deviation from five determinations of cobalt at a concentration of 5 × 10^–9 mol L⁻¹ was 5.2%. The detection limit for an accumulation time of 300 s was 1.8 × 10^–11 mol L⁻¹. The proposed procedure was applied to cobalt determination in certified reference materials and in tap and river water samples.

Keywords: Cobalt; Determination; Bismuth film electrode

Investigations into the electrooxidation of guanosine-5′-triphosphate at the pyrolytic graphite electrode by Rajendra N. Goyal; Anuradha Tyagi (pp. 1683-1690).

The electrochemical oxidation of guanosine-5′-triphosphate has been investigated in phosphate-containing electrolytes in the pH range 1.5–10.9 at a pyrolytic graphite electrode by cyclic sweep voltammetry, spectral studies, bulk electrolysis and related techniques. In this pH range, the oxidation occurred in a single well-defined peak (I_a). The peak potential of oxidation peaks (E_p) was found to be dependent on pH, concentration and sweep rate. The kinetics of the UV-absorbing intermediates was followed spectrophotometrically and the decay of the intermediate occurred in a pseudo-first-order reaction. The first-order rate constants for the disappearance of the UV-absorbing intermediate have also been calculated. The products of the electrode reaction were characterized by HPLC and GC/MS. A tentative mechanism for the formation of the products has also been suggested.

Keywords: Guanosine-5′-triphosphate; Electrooxidation; Purine nucleotides; Voltammetric studies

Application of a bismuth film electrode to the voltammetric determination of trace iron using a Fe(III)–TEA–BrO₃⁻ catalytic system by A. Bobrowski; K. Nowak; J. Zarębski (pp. 1691-1697).

A sensitive catalytic voltammetric method for determining trace iron at a bismuth film electrode (BiFE) is described. The method is based on the cathodic reduction of the Fe(III)–triethanolamine (TEA) complex to Fe(II). It has been proved that the addition of KBrO₃ causes rapid oxidation of Fe(II) and TEA, and therefore results in a large increase in the analytical signal from Fe(III) when TEA is placed in alkaline solution. When TEA was present in the solution, operating the BiFE under optimized conditions yielded a stable catalytic voltammetric response for iron, with high sensitivity (0.88 μA μM⁻¹), good precision (RSD=3.9%) and a low detection limit (7.7×10⁻⁹ M), obtained without any preconcentration procedure. Possible interferences from the coexisting ions and surface-active substances were investigated. Finally, the method was applied with satisfactory results to the determination of iron in certified reference river water samples.

Keywords: Voltammetry; Catalytic effect; Iron; Bismuth film electrode

Preparation of a novel molecularly imprinted polymer using a water-soluble crosslinking agent by Takuya Kubo; Ken Hosoya; Makoto Nomachi; Nobuo Tanaka; Kunimitsu Kaya (pp. 1698-1701).

A molecularly imprinted polymer was prepared using a water-soluble crosslinking agent. An ionic complex was utilized as the assembly for the template molecule and the functional monomer, and water as porogenic solvent during preparation of the imprinted polymer. The results of chromatographic evaluations for the prepared polymer suggested that the polymer had much lower hydrophobicity compared with usual octadecyl group bonded silica or the usual molecular imprinted polymer prepared from ethyleneglycol dimethacrylate, and the selective recognition ability for template molecule in the completely aqueous condition.

Keywords: Molecularly imprinted polymer; Water-soluble crosslinking agent; Ionic complex; Lower hydrophobicity; Selective recognition

One-milliliter wet-digestion for inductively coupled plasma mass spectrometry (ICP-MS): determination of platinum-DNA adducts in cells treated with platinum(II) complexes by Kanae Yamada; Naoyuki Kato; Akimitsu Takagi; Minoru Koi; Hiromichi Hemmi (pp. 1702-1707).

Platinum (Pt)–DNA adducts formed by the anti-tumor agent cisplatin are recognized by the DNA mismatch repair (MMR) system. To investigate the involvement of MMR proteins including hMLH1 in the removal of these adducts, we developed a mL-scale wet-digestion method for inductively coupled plasma mass spectrometry (ICP-MS). The detection limit was 0.01 ng mL⁻¹ Pt, which corresponded to 2 pg Pt/μg DNA when 10 μg of DNA was used. The mean relative errors were 5.4% or better for a dynamic range of 0.01–10 ng mL⁻¹ Pt. DNA (~500 μg) had no matrix effect. To improve the accuracy, DNA preparations were treated with ribonuclease and the apparent reduction in the concentration of Pt was corrected using cellular DNA levels, which were determined with Hoechst 33258. No significant differences were observed, in terms of the formation of Pt–DNA adducts or their removal over 6 h, between hMLH1-deficient HCT116 cells, a human colorectal cancer cell line, and hMLH1-complemented HCT116+ch3 cells (n=5; P>0.05), indicating that the hMLH1-dependent DNA repair systems contribute to neither the formation nor the removal of the adducts at detectable levels. In addition, approximately 19% of the adducts were removed within 6 h in both cell lines. A time course analysis (~24 h) suggested that the removal of cisplatin-generated Pt–DNA adducts follows first-order kinetics (t_1/2=32 h). The amount of Pt–DNA adduct formed by oxaliplatin in 1 h was 56% (ratio of means) of that generated by an equimolar concentration of cisplatin in HCT116. The proposed procedure could be useful for determining Pt–DNA adducts formed by Pt(II) complexes.

Keywords: Cisplatin; Platinum; DNA adducts; Mismatch repair; Inductively-coupled plasma mass spectrometry; Wet digestion

Colorimetric detection of oligonucleotides using a polydiacetylene vesicle sensor by Chungang Wang; Zhanfang Ma (pp. 1708-1710).

A new system for the colorimetric detection of oligonucleotides was developed using polydiacetylene vesicles, which play the dual role of an indicator of color transition and an amplification tag. The results are of significance in understanding the mechanism of color transition of biological recognition in polydiacetylene systems and in designing new biosensors.

Keywords: Polydiacetylene vesicles; Oligonucleotide detection

Application of a chemometric method for simultaneous determination of acetaminophen and diclofenac in content-uniformity and drug-dissolution studies by Patricia M. Castellano; Silvana E. Vignaduzzo; Rubén M. Maggio; Teodoro S. Kaufman (pp. 1711-1714).

A new, repeatable, and rapid method has been developed for resolution of binary mixtures of acetaminophen and diclofenac with minimum sample pretreatment and without separation of the analytes. The method, based on the PLS1 processing of absorbance data in the UV region, was successfully used for quantification of the drug content of three tablet preparations. The results obtained were in good agreement with HPLC recovery data. The method also enabled determination of drug-dissolution profiles of these commercial tablets, by simultaneous determination of both analytes during the dissolution test.

Keywords: Chemometric method; Acetaminophen; Diclofenac; PLS; Dissolution

Mercury depth profiles in river and marine sediments measured by the diffusive gradients in thin films technique with two different specific resins by P. Diviš; M. Leermakers; H. Dočekalová; Y. Gao (pp. 1715-1719).

The diffusive gradients in thin films technique (DGT) was used to measure depth profiles of mercury in river and marine sediments in situ to a spatial resolution of 0.5 cm. Agarose gel was used as the diffusive gel in the DGT probes. Two different selective resins—Chelex 100 with iminodiacetic groups and Spheron-Thiol with thiol groups incorporated in the polyacrylamide resin gel—were tested. The different capture efficiencies of the two adsorbents enabled the fractions of mercury bound in different species in sediment pore water to be estimated. Mercury concentrations obtained by DGT with Spheron-Thiol resin were very similar to those obtained after centrifugation. This indicates that DGT with Sheron-Thiol resin reports on total dissolved mercury levels. The concentration of mercury measured by DGT with Chelex-100 resin was much lower (by a factor of 5–20) for the same sediment samples. Chelex-100 does not have such a high affinity to mercury as Spheron-Thiol, and so it only reports on the content of labile mercury species, such as inorganic ions and weak complexes. The content of labile mercury species in the river sediment was approximately 20% of the total dissolved mercury in pore water, whereas in marine sediment only 7% of the mercury was present as labile species.

Keywords: Diffusive gradients in thin films technique (DGT); Mercury; Sediment; Pore water

Electroanalytical method for determination of the pesticide dichlorvos using gold-disk microelectrodes by Djenaine De Souza; Sergio A. S. Machado (pp. 1720-1725).

This paper reports the use of laboratory-prepared gold microelectrodes and square-wave voltammetry for analytical determination of low concentrations of the pesticide dichlorvos in pure and natural water samples. After optimization of the experimental and voltammetric conditions, the best voltammetric responses—current intensity and voltammetric profile—were obtained in 0.1 mol L⁻¹ NaClO₄ with f=100 s⁻¹, a=50 mV, and ΔE_s=2 mV. The observed detection and quantification limits in pure water were 7.8 and 26.0 μg L⁻¹, respectively. The reproducibility and repeatability of the method were also determined; the results were 1.4% (n=5) and 1.2% (n=10), respectively. Possible interfering effects were evaluated in natural water samples collected at different points with different levels of contamination from agricultural, domestic, or industrial waste from an urban stream. Results showed that the detection and quantification limits increased as a function of the quantity of organic matter present in the samples. Nonetheless, the values observed for these method characteristics were below the maximum value allowed by the Brazilian code for organophosphorus pesticides in water samples. Recovery curves constructed using the standard addition method were shown to be satisfactory compared with those obtained from high-performance liquid chromatography, confirming the suitability of the method for analysis of natural water samples. Finally, when the method was used to determine dichlorvos in spiked cows’ milk samples, satisfactory recovery and relative standard deviations were obtained.

Keywords: Microelectrodes; Dichlorvos pesticide; Square-wave voltammetry

2006 Bunsen–Kirchhoff Award for Analytical Spectroscopy by Hugo M. Ortner (pp. 1726-1726).

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Analytical and Bioanalytical Chemistry (v.382, #7)

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Analytical and Bioanalytical Chemistry (v.382, #7)