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Analytica Chimica Acta (v.530, #2)

Contents (pp. iii-iv).

Filler Ad.: ACAEES (pp. ii).

Calendar of forthcoming meetings (pp. n5-n7).

Outside front cover - Editorial Board (pp. co1).

Investigation of sera from various species by using lectin affinity arrays and scanning ellipsometry by Jenny Carlsson; Michael Mecklenburg; Ingemar Lundstr�m; Bengt Danielsson; Fredrik Winquist (pp. 167-171).

Serum proteins of different species and of different human blood groups exhibit various protein glycosylation patterns. Sera from human, pig, sheep and guinea pig have been applied to a panel of eight different lectins immobilized on a gold wafer. The biorecognition has been evaluated with scanning ellipsometry and the two-dimensional matrices obtained have been treated with image analysis and MVDA for evaluation. The results showed a clear difference in protein binding pattern between the different species and thereby separation of the different sera could be made. Dendograms indicate that human and pig sera are the most related of the four different sera investigated.

Keywords: Serum proteins; Lectins; Scanning ellipsometry; Image analysis; Multivariate data analysis

Multilevel component analysis of time-resolved metabolic fingerprinting data by Jeroen J. Jansen; Huub C.J. Hoefsloot; Jan van der Greef; Marieke E. Timmerman; Age K. Smilde (pp. 173-183).

Genomics-based technologies in systems biology have gained a lot of popularity in recent years. These technologies generate large amounts of data. To obtain information from this data, multivariate data analysis methods are required. Many of the datasets generated in genomics are multilevel datasets, in which the variation occurs on different levels simultaneously (e.g. variation between organisms and variation in time). We introduce multilevel component analysis (MCA) into the field of metabolic fingerprinting to separate these different types of variation. This is in contrast to the commonly used principal component analysis (PCA) that is not capable of doing this: in a PCA model the different types of variation in a multilevel dataset are confounded.MCA generates different submodels for different types of variation. These submodels are lower-dimensional component models in which the variation is approximated. These models are easier to interpret than the original data. Multilevel simultaneous component analysis (MSCA) is a method within the class of MCA models with increased interpretability, due to the fact that the time-resolved variation of all individuals is expressed in the same subspace.MSCA is applied on a time-resolved metabolomics dataset. This dataset contains¹H NMR spectra of urine collected from 10 monkeys at 29 time-points during 2 months. The MSCA model contains a submodel describing the biorhythms in the urine composition and a submodel describing the variation between the animals. Using MSCA the largest biorhythms in the urine composition and the largest variation between the animals are identified.Comparison of the MSCA model to a PCA model of this data shows that the MSCA model is better interpretable: the MSCA model gives a better view on the different types of variation in the data since they are not confounded.

Keywords: NMR; Principal component analysis; Urinalysis; Metabolomics; Biorhythms; Types of variation

Determination of organophosphate pesticides at a carbon nanotube/organophosphorus hydrolase electrochemical biosensor by Randhir Prakash Deo; Joseph Wang; Ines Block; Ashok Mulchandani; Kanchan A. Joshi; Marek Trojanowicz; Fritz Scholz; Wilfred Chen; Yuehe Lin (pp. 185-189).

An amperometric biosensor for oganophosphorus (OP) pesticides based on a carbon nanotube (CNT)-modified transducer and an organophosphorus hydrolase (OPH) biocatalyst is described. A bilayer approach with the OPH layer atop of the CNT film was used for preparing the CNT/OPH biosensor. The CNT layer leads to a greatly improved anodic detection of the enzymatically generated p-nitrophenol product, including higher sensitivity and stability. The sensor performance was optimized with respect to the surface modification and operating conditions. Under the optimal conditions the biosensor was used to measure as low as 0.15μM paraoxon and 0.8μM methyl parathion with sensitivities of 25 and 6nA/μM, respectively.

Keywords: OPH; CNT; Biosensors; Oganophosphorus compounds; Nitrophenol

Compact amperometric algal biosensors for the evaluation of water toxicity by Isao Shitanda; Kazutake Takada; Yasuyuki Sakai; Tetsu Tatsuma (pp. 191-197).

Unicellular microalga Chlorella vulgaris was entrapped in an alginate gel or a polyion complex membrane immobilized directly on the surface of a transparent indium tin oxide electrode. Photosynthetically generated oxygen of the immobilized algae was monitored amperometically. Responses of the algal biosensor to four toxic compounds, 6-chloro- N-ethyl- N-isopropyl-1,3,5-triazine-2,4-diamine (atrazine), 3-(3,4-dichlorophenyl)-1,1-diethylurea (DCMU), toluene and benzene, were evaluated as inhibition ratios of the reduction current. The concentrations that give 50% inhibition of the oxygen reduction current (IC′50) for atrazine, DCMU, toluene and benzene were 2.0, 0.05, 1550 and 3000μmoldm⁻³, respectively. There was a good correlation between these data and those of the conventional standard growth test. In comparison with the conventional algal biosensors based on the Clark-type oxygen electrode, the present sensor is much smaller and less expensive, and its assay time is much shorter (≤200s).

Keywords: Amperometric biosensor; Chlorella vulgaris; Algae; Alginate gel; Polyion complex; Herbicides

Lowering the detection limit of the acetylcholinesterase biosensor using a nanoporous carbon matrix by Sofia Sotiropoulou; Nikos A. Chaniotakis (pp. 199-204).

Nanostructured carbon matrix has been used for the immobilization and stabilization of the enzyme E.el. AChE. The use of this activated carbon matrix is shown to provide both, significant enzyme stabilization, as well as the means for lowering the detection limit of the biosensor. The enzyme is immobilized by adsorption into the nanostructured conductive carbon, which also acts as the working electrode. The proposed biosensor showed very good stability under continuous operation conditions ( L₅₀>60 days), allowing its further use in inhibition mode. Using this biosensor, the monitoring of the organophosphorus pesticide dichlorvos at picomolar levels (1000 times lower than other systems reported so far) was achieved. The linear range of detection in flow injection system was six orders of magnitude (10⁻¹² to 10⁻⁶M). It is suggested that the ability of activated carbon to selectively concentrate the pesticide, as well as the enzyme hyperactivity within the nanopores is the reason for the decrease in the detection limit of the biosensor.

Keywords: Selective concentration; Biosensor; Picomolar; Dichlorvos

Microbiosensor for acetylcholine and choline based on electropolymerization/sol–gel derived composite membrane by Minghui Yang; Yunhui Yang; Yu Yang; Guoli Shen; Ruqin Yu (pp. 205-211).

Amperometric enzyme biosensors for the determination of acetylcholine (ACh) and choline (Ch) have been described. For the fabrication of the biosensors, N-acetylaniline (nAN) was first electropolymerized on a Pt electrode surface to be served as a permselective layer to reject interferences. Bovine serum albumin (BSA) and choline oxidase (CHOD) were co-immobilized in a zinc oxide (ZnO) sol–gel membrane on the above modified Pt electrode for a Ch sensor, or CHOD, acetylcholinesterase (AChE) and BSA immobilized together for an ACh/Ch sensor. The poly ( N-acetylaniline) (pnAN) film was the first time used for an ACh/Ch sensor and found to have excellent anti-interference ability, and the BSA in the sol–gel can improve the stability and activity of the enzymes. Amperometric detection of ACh and Ch were realized at an applied potential of +0.6V versus SCE. The resulting sensors were characterized by fast response, expanded linear range and low interference from endogenous electroactive species. Temperature and pH dependence and stability of the sensor were investigated. The optimal ACh/Ch sensor gave a linear response range of 1.0×10⁻⁶ to 1.5×10⁻³M to ACh with a detection limit (S/N=3) of 6.0×10⁻⁷M and a linear response range up to 1.6×10⁻³M to Ch with a detection limit of 5.0×10⁻⁷M. The biosensor demonstrated a 95% response within less than 10s.

Keywords: Amperometric biosensor; Acetylcholine; Choline; N; -Acetylaniline; nAN electropolymerization; Sol–gel

Characterization of cyclodextrin modified infrared chemical sensors. Part II. Selective and quantitative determination of aromatic acids by Jyisy Yang; Huang-Jei Lin; Hsi-Ya Huang (pp. 213-220).

In this paper, the selectivity and sensitivity of cyclodextrin (CD) modified infrared (IR) chemical sensor in detection of aromatic acids in aqueous solutions were reported. To eliminate the interference from water, the technique of attenuated total reflection was employed. By surface treated with CD molecules on the internal reflection elements, the sensors were selective in sensing of aromatic acids compared to aromatic compounds with other functional groups. To facilitate the use of this method for the quantitative analyses of aromatic acids in aqueous solutions, analytical functions were also developed in this work and a linear relationship between analytical responses and concentrations of analytes can be obtained. To optimize the analytical conditions, the factors that influence the IR spectroscopic signals were examined. These factors included response time, CD loadings of the sensors, pH effect on response, regeneration efficiency and stability of sensors. Under the optimal conditions, the detection limits for aromatic acids at a detection time of 2min can be <100μg/L. Meanwhile, the dynamic linear range for detection was only ca. two orders of magnitude if direct IR signals were used. Using the analytical function developed in this work, the linearity can be extended up to a concentration of 100mg/L.

Keywords: Cyclodextrin; Attenuated total reflection; Evanescent wave; Infrared; FT-IR spectroscopy

Fluorometric quantification of totald-gluconate by a flow-injection system using an immobilized-enzyme reactor by Tadayuki Tsukatani; Kiyoshi Matsumoto (pp. 221-225).

A method for the quantification of totald-gluconate by flow-injection analysis was developed using an immobilized-enzyme reactor and fluorescence detection.d-Gluconate was quantified using co-immobilized gluconate kinase (GK) and 6-phosphogluconate dehydrogenase (PGDH) reactor.d-Gluconate was phosphorylated to 6-phospho-d-gluconate by GK in the presence of ATP, and then the 6-phospho-d-gluconate produced was oxidized by PGDH with NADP⁺. The NADPH produced by the GK-PGDH reactor was monitored fluorometrically at 455nm (excitation at 340nm). A linear relationship between the responses and concentrations ofd-gluconate was obtained in the ranges of 1.0×10⁻⁶–1.6×10⁻⁴M. The relative standard deviation for 10 successive injections was 0.57% at the 0.1mM level. This analytical method was applied to the quantification ofd-gluconate in honeys, vinegars and noble rot wines, and the results showed good agreement with those obtained using the conventional F-kit method.

Keywords: Flow-injection analysis; Immobilized-enzyme reactor; d; -Gluconate; Honey; Vinegar; Noble rot wine

Nano-flow multidimensional liquid chromatography with electrospray ionization time-of-flight mass spectrometry for proteome analysis of hepatocellular carcinoma by Yan Wang; Jie Zhang; Chun-Li Liu; Xue Gu; Xiang-Min Zhang (pp. 227-235).

Hepatocellular carcinoma (HCC) is one of the top five cancers with the highest incident of a disease worldwide. To understand the mechanisms of hepatocarcinogenesis, proteomics analysis provides a powerful tool to identify proteins that associate with HCC. We developed a two-step procedure for mapping of HCC proteomics. In the first step, in order to simplify the complexity of proteomics of HCC, the subfractionation of complex protein mixtures in HCC into “subproteomes�? is presented based on the solubility of protein. While in the second step an automate comprehensive two-dimensional (2D) separation system, coupling strong cation-exchange (SCX) in the first dimension with capillary reversed-phase chromatography (cRPLC) in the second dimension is developed further to separate and analyze proteins associated with HCC. By using this system, complex sample can be injected, desalted, separated and analyzed in complete automatization. The procedure for proteomics analysis was found to be applied for proteins with great molecular mass (>100000), small molecular mass (<20000), highly basic (p I>9.5) and hydrophobicity, which are not well resolved in 2D-gel electrophoresis. In total 229 proteins were identified by using the described proteomics platform. Among them, several proteins related to the process of carcinogenesis were investigated further.

Keywords: Human hepatocellular carcinoma; Two-dimensional liquid chromatography; Electrospray ionization mass spectrometer; Proteomics; Nano-flow

Residue determination of cyromazine and its metabolite melamine in chard samples by ion-pair liquid chromatography coupled to electrospray tandem mass spectrometry by J.V. Sancho; M. Ib��ez; S. Grimalt; �.J. Pozo; F. Hern�ndez (pp. 237-243).

A method has been developed for the sensitive and selective determination of cyromazine and its metabolite melamine in chard samples. Both compounds are small polar basic molecules, making their determination at residue levels complicated. The method involves an extraction procedure with phosphate buffer and methanol using high-speed blender, the addition of tridecafluoroheptanoic acid (TFHA) as ion-pair reagent and the injection of the five-fold diluted extract on liquid chromatography coupled to electrospray tandem mass spectrometry (LC–ESI–MS/MS). The method has been validated for chard samples, spiked at 0.05 and 0.5mgkg⁻¹. Quantification was carried out by using matrix-matched standards calibration and recoveries were satisfactory, with mean values for cyromazine of 103% and 93%, and relative standard deviations lower than 7%. In the case of melamine, recoveries were 89% and 86%, with relative standard deviations lower than 13%. A limit of quantification of 0.05mgkg⁻¹ was obtained for both compounds, with the limit of detection below 0.01mgkg⁻¹. The method, with very little sample handling and good sensitivity, was applied to the rapid determination of low residue levels of these compounds in chards from field residue trials. All the quality controls included during the analysis were satisfactory with average recoveries of 92% and 78% for cyromazine and melamine, respectively.

Keywords: Cyromazine; Melamine; Pesticide residues; Vegetables; Liquid chromatography; Tandem mass spectrometry

Determination of alkylphenol and bisphenol A in beverages using liquid chromatography/electrospray ionization tandem mass spectrometry by Bing Shao; Hao Han; Jianying Hu; Jie Zhao; Guohua Wu; Ying Xue; Yalu Ma; Shujun Zhang (pp. 245-252).

A comprehensive analytical method based on liquid chromatography electrospray ionization tandem mass spectrometry (LC–ESI–MS/MS) with negative ionization mode has been developed for measuring of alkylphenols and bisphenol A in beverage samples. Concentration and clean up of samples were performed on 200mg OASIS HLB solid extraction cartridges. The effects of mobile phases and additives on ionization were assessed. The recoveries for each compound ranged from 76.7 to 96.9% and reproducibilities were represented as having relative standard deviation (R.S.D.) below 10%. The limits of quantification (LOQ) of the method under multiple-reaction monitoring (MRM) acquisition mode were 0.04, 0.03 and 0.2ngL⁻¹ for 2L of mineral drinking water and 2.0, 1.8 and 8.0ngL⁻¹ for 50mL of soda beverages.

Keywords: Alkylphenol; Bisphenol A; LC–ESI–MS/MS

Pyrolysis–GC–MS to trace terrigenous organic matter in marine sediments: a comparison between pyrolytic and lipid markers in the Adriatic Sea by Daniele Fabbri; Francesca Sangiorgi; Ivano Vassura (pp. 253-261).

The effectiveness of semiquantitative pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) as a rapid analytical technique for sourcing continental organic matter (OM) in marine sediments was examined by comparison with classical GC–MS analyses of solvent extractable lipid markers. Py–GC–MS was directly applied to HCl/HF de-ashed surface sediment samples collected in five stations located in north western Adriatic Sea. The resulting pyrolysates were characterised by compounds indicative of different biological precursors (e.g. proteins, carbohydrates, chlorophylls), including lignin methoxyphenols diagnostic for continental inputs. The relative abundance of pyrolytic markers was compared to the distribution of n-alkanes, n-alkanols and sterols extracted from the same sediments and determined by GC–MS analyses. For each class of molecular indicators, the terrigenous to aquatic ratio (TAR) was determined as follows: relative abundance of methoxyphenol/protein markers (TAR_PY), concentration ratios of (C27+C29+C31)/(C15+C17+C19) n-alkanes (TAR_HC), (C26+C28+C30)/(C14+C16) n-alkanols (TAR_AL) and sitosterol/cholesterol (TAR_ST). A positive correlation was found between TAR_PY and both TAR_HC and TAR_AL indicating a decreasing contribution of land-plant-derived materials seaward in two investigated transects. TAR_ST values displayed a different trend suggesting a mixed origin for sitosterol. The distribution of TAR_PY values was also in good agreement with that of atomic C/N ratios. Considering the complexity of environmental systems (diagenetic alteration, different fractions of OM analysed) the obtained results indicate that the pyrolytic marker approach by Py–GC–MS is valuable for sourcing marine OM on a semiquantitative base, providing data consistent with GC–MS determinations of lipid markers and elemental bulk analyses.

Keywords: Pyrolysis–GC–MS; Terrigenous organic matter; Marine sediments; Lignin markers; Lipid markers; Adriatic Sea

Stability of workroom air volatile organic compounds on solid adsorbents for thermal desorption gas chromatography by Jon Volden; Yngvar Thomassen; Tyge Greibrokk; Syvert Thorud; Paal Molander (pp. 263-271).

The storage stability of the occupationally frequently occurring compounds, methylethylketone, methylisobutylketone, benzene, toluene, tetrachloroethylene, n-butylacetate, α-pinene, β-pinene, limonene and n-decane, has been investigated on the adsorbents Tenax TA, Chromosorb 106 and Carbotrap using thermally desorbable tube type samplers, commonly utilized in ambient and workroom atmospheric measurements. Fifty and 500ng of each compound were loaded on the various adsorbents tubes, stored at both ambient (20°C) and refrigerated (4°C) temperatures and analysed by means of thermal gas chromatography with mass spectrometric detection on days 0, 7, 14 and 28 after exposure. A 90% storage recovery was chosen as acceptance criteria for storage stability, and statistical testing by Student's t-test, analysis of variance and Bonferroni post hoc tests were employed to investigate the effect of the categorical variables storage time, storage temperature and analyte loading on the different adsorbents. Chromosorb 106 showed the overall best behaviour with recoveries of 90% or better for all analytes during the 28-day test period. Tenax TA and Carbotrap yielded lower recoveries and were more influenced by variations in storage time, storage temperature and analyte loading. Refrigerated temperatures were best avoided for storage on Tenax TA, but may increase the recovery of some compounds on Carbotrap (e.g. n-butylacetate). The blank build-up on the adsorbents was also investigated, and Carbotrap and Tenax TA showed no signs of artefact development over time. Chromosorb 106, however, contained inherently more artefacts that build up over time, which in spite of the excellent storage capability, may limit its use in field studies where long storage times are normal.

Keywords: Air sampling; Solid adsorbents; Thermal desorption; Volatile organic compounds (VOCs); Tenax TA; Chromosorb 106; Carbotrap; Storage stability; Blank build-up

Effects of surface heterogeneity on flow circulation in electroosmotic flow in microchannels by Jacky S.H. Lee; Carolyn L. Ren; Dongqing Li (pp. 273-282).

The characteristics of electroosmotic flow in a cylindrical microchannel with non-uniform zeta potential distribution are investigated in this paper. Two-dimensional full Navier–Stokes equation is used to model the flow field and the pressure field. The numerical results show the distorted electroosmotic velocity profiles and various kinds of flow circulation resulting from the axial variation of the zeta potential. The influences of heterogeneous patterns of zeta potential on the velocity profile, the induced pressure distribution and the volumetric flow rate are discussed in this paper. This work shows that using either heterogeneous patterns of zeta potential or a combination of a heterogeneous zeta potential distribution and an applied pressure difference over the channel can generate local flow circulations and hence provide effective means to improve the mixing between different solutions in microchannels.

Keywords: Electroosmotic; Heterogeneous; Microchannel

Continuous flow autoanalyzer for the sequential determination of total sugars, colorant and caffeine contents in soft drinks by Rafael Lucena; Soledad C�rdenas; Mercedes Gallego; Miguel Valc�rcel (pp. 283-289).

A novel autoanalyzer for sequential determination of total sugars, class IV caramel and caffeine contents in soft drinks is described for the first time. The multiparametric autoanalyzer is based on the on-line coupling of a continuous solid-phase extraction unit with two detectors in series: UV–vis and evaporative light scattering (ELSD) detectors. Caffeine is selectively retained on the sorbent column and the other components are sequentially determined in the effluent. Caffeine was further eluted with an acetonitrile stream and the signal registered in the ELSD. The proposed autoanalyzer is a useful tool for the determination of these macrocomponents in the selected matrices on account of the high level of capital, basic and productivity-related analytical properties it provides. The method was validated through the use of spiked samples and applied to the analysis of more than 20 different soft drink samples (regular, diet, caffeine-free, energy drinks) with satisfactory results.

Keywords: Total sugars; Caramel and caffeine; Soft drinks; Solid-phase extraction; Multiparametric autoanalyzer

Analytical procedures for improved trace element detection limits in polar ice from Arctic Canada using ICP-SMS by Michael Krachler; James Zheng; David Fisher; William Shotyk (pp. 291-298).

Analytical procedures have been developed for the reliable determination of 19 trace elements (Ag, Al, Ba, Bi, Cd, Co, Cr, Cu, Fe, Mn, Pb, Rb, Sb, Sc, Sr, Tl, U, V, Zn) in ice samples at pgg⁻¹ and fgg⁻¹ concentrations using ICP-sector field mass spectrometry (ICP-SMS). Concentrations of most elements in the high purity water and doubly distilled HNO₃ employed were distinctly lower than previously reported values. The accuracy of the results was carefully evaluated using the certified water reference material SLRS-4. Contributions of unwanted trace elements due to acidification of the ice samples (0.5% HNO₃) to the total element budget amounted to only 0.001pgg⁻¹ for Bi, 0.34pgg⁻¹ for Cr, 0.2pgg⁻¹ for Fe, 0.004pgg⁻¹ for Pb, 0.00015pgg⁻¹ for U and 0.0025pgg⁻¹ for V: compared to the concentrations of the metals in ice these are negligible. The use of a detergent (0.05%) in the rinsing solution (0.5% HNO₃), helped to reduce memory effects by 59–98%, depending on the element considered; this resulted in shorter washing times between samples (i.e. 1min) and improved analysis time. Adopting strict clean room procedures, the detection limit for Pb (0.06pgg⁻¹) is a factor of ten lower than the current state-of-the-art. Compared to previous studies, the improved LODs obtained here for other trace elements amount to 2× (Ag), 4× (Sb), 5× (Ba), 6× (Cu, Mn, U), 9× (Bi), 13× (Cd), 18× (Fe) and 21× (V). The developed analytical protocols were successfully applied to the determination of selected trace elements in age-dated ice samples from the Canadian High Arctic. The toxic trace element Tl (median: 0.16pgg⁻¹; range: 0.03–1.32pgg⁻¹) and the lithogenic reference element Sc (0.53pgg⁻¹; 0.06–2.9pgg⁻¹) have been determined in a polar ice core for the first time.

Keywords: Trace elements; Ice; ICP-MS; Arctic; Scandium; Thallium

Evaluation of a synergetic effect between Rh as permanent chemical modifier and acetylacetone as complexing agent in Sc determination in sediment slurry samples by ETAAS by Araceli Ver�nica Flores; Carlos Alberto P�rez; Marco Aur�lio Zezzi Arruda (pp. 299-305).

In the present work, scandium was determined in sediment slurry samples (from three different rivers) by electrothermal atomic absorption spectrometry (ETAAS). Slurries were prepared by weighting 100mg of dry sediment samples (≤53μm particle sizes) and adding 6ml of HCl:HNO₃:HF (3:1:2, v/v). Accurate results were only possible due to the synergetic effect between Rh as permanent chemical modifier and acetylacetone (Acac) as complexing agent. The same platform was used for 400 heating cycles. The performance of the chemical modification was evaluated by using scanning electron microscopy (SEM), synchrotron radiation X-ray fluorescence (SRXRF) and some figures of merit (precision and detectability). The best analytical conditions were attained using 1500 and 2550°C as pyrolysis and atomization temperatures. The scandium content in the liquid phase of the slurries ranged from 61 to 73%, thus indicating, in this study, that both liquid and solid phases play an important role in slurry analyses. An amount of 5.0–20.0μgl⁻¹ Sc linear range as well as LOD and LOQ of 0.19 and 0.62μgl⁻¹, respectively, were obtained under these conditions. The accuracy was checked by using microwave-assisted decomposition, and the results compared to those obtained with the proposed methodology (slurry analysis). By checking both sets of the results, there is no statistical difference at the 95% confidence levels.

Keywords: Scandium; Slurry river sediment; Permanent chemical modifier; Complexing agent; Electrothermal atomic absorption spectrometry; Synchrotron radiation X-ray fluorescence; Scanning electron microscopy

Direct determination of arsenic in acid digests of plant and peat samples using HG-AAS and ICP-SF-MS by Jutta Frank; Michael Krachler; William Shotyk (pp. 307-316).

A new analytical procedure for the reliable and direct determination of arsenic (As) in nitric acid digests of ombrotrophic peat samples in the low ngl⁻¹ range has been developed based on hydride generation-atomic absorption spectrometry (HG-AAS). The pre-reduction capabilities of KI/ascorbic acid and ofl-cysteine in nitric acid digests of peat and plant samples for the conversion of As(V) to As(III) were tested systematically. Samples were digested with high purity nitric acid in a high-pressure microwave autoclave at 240°C and subsequently measured using HG-AAS or ICP-SF-MS (inductively coupled plasma-sector field-mass spectrometry). Using KI/ascorbic acid as pre-reductant, the accuracy and precision were poor when digests of complex matrices, such as peat were analyzed for As by HG-AAS. However, 10gl⁻¹l-cysteine was successfully employed as pre-reductant in diluted nitric acid digests (∼3%, v/v) of peat samples prior to hydride generation of As with 0.5% (m/v) of NaBH₄ and 7moll⁻¹ HCl. The analytical procedure was critically evaluated by analyzing several certified plant reference materials, two in-house peat reference materials and by the determination of As in diluted digests of peat samples with ICP-SF-MS. The results for the determination of As in various peat and plant materials showed excellent agreement with the reference values. The method detection limits for the determination of As by the optimized HG-AAS procedure and by ICP-SF-MS were 23ngg⁻¹ and 1.4ngg⁻¹ in solid peat, respectively. The newly developed analytical procedure was applied to the determination of As in selected peat samples. Results for As in these peat samples obtained by the developed HG-AAS procedure and the optimized procedure for the determination of As with ICP-SF-MS were highly correlated ( R²=0.993, n=12).

Keywords: Arsenic; HG-AAS; ICP-SF-MS; Peat; Microwave digestion

A novel method for determination of peroxynitrite based on hemoglobin catalyzed reaction by Ju Liang; Zhi-Hong Liu; Ru-Xiu Cai (pp. 317-324).

A novel spectrofluorimetric method for the determination of peroxynitrite is proposed. The method is based on a mimetic enzyme catalyzed reaction with hemoglobin as the catalyst andl-tyrosine as the substrate. A new fluorescent substance is produced that might probably be the coupled dimmer of tyrosine, which, instead of nitryl-tyrosine, is likely to be a new marking substance of ONOO⁻ injury in vivo. Kinetics of the reaction is studied and the possible reaction mechanism is also recommended. The proposed method is simple and highly sensitive with a detection limit of 5.00×10⁻⁸molL⁻¹ of peroxynitrite. A liner calibration graph is obtained over the peroxynitrite concentration range 5.60×10⁻⁷ to 2.10×10⁻⁵molL⁻¹, with a correlation coefficient of 0.9983. Interferences from some amino acids and metal ions normally seen in biological samples, and also some anions structurally similar to ONOO⁻ are studied.

Keywords: Peroxynitrite; Enzymatic method; Hemoglobin; l; -Tyrosine; Kinetics

A solid phase microextraction method to fingerprint dissolved organic carbon released from Eucalyptus camaldulensis (Dehnh.) (River Red Gum) leaves by Alek Zander; Andrea G. Bishop; Paul D. Prenzler (pp. 325-333).

A solid phase microextraction-gas chromatography (SPME-GC) method was developed to trace natural sources of dissolved organic carbon (DOC) in river systems. The effects of extraction time, temperature, salt concentration, rate of stirring, and silanisation of sampling container were examined. The optimum extraction conditions using a polydimethylsiloxane (PDMS) SPME fibre were found to be extraction for 15min at 40°C, pH 2, from a saturated NaCl matrix with rapid stirring in a non-silanised vial. The method gave good results for a series of six compounds representative of those likely to be present in dissolved organic carbon leached from River Red Gum leaves—cineole, terpineol, thymol, myristic acid, methyl palmitate and methyl stearate. Artificial dissolved organic carbon solutions prepared from River Red Gum leaf leachate were also examined and the effects of filtering and storage on the filtrate were noted. The method was demonstrated to have potential to track the leachate in aquatic environment, indicated by the large number of compounds extracted from leachate solutions, and the broad linear working ranges of extracted compounds.

Keywords: SPME; SPME-GC; Water analysis; Environmental analysis; DOC

Erratum to “Development of a capillary gas chromatographic procedure�? [Anal. Chim. Acta 519 (2004) 219–230] by J.J. Berzas; C. Guiberteau; M.J. Villase�or; V. Rodr�guez (pp. 335-335).

Author Index (pp. 337-339).

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Analytica Chimica Acta (v.530, #2)