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Analytical and Bioanalytical Chemistry (v.384, #7-8)

Strategies for the microextraction of polar organic contaminants in water samples by José Benito Quintana; Isaac Rodríguez (pp. 1447-1461).

In this paper the most recent developments in the microextraction of polar analytes from aqueous environmental samples are critically reviewed. The particularities of different microextraction approaches, mainly solid-phase microextraction (SPME), stir-bar-sorptive extraction (SBSE), and liquid-phase microextraction (LPME), and their suitability for use in combination with chromatographic or electrically driven separation techniques for determination of polar species are discussed. The compatibility of microextraction techniques, especially SPME, with different derivatisation strategies enabling GC determination of polar analytes and improving their extractability is revised. In addition to the use of derivatisation reactions, the possibility of enhancing the yield of solid-phase microextraction methods for polar analytes by using new coatings and/or larger amounts of sorbent is also considered. Finally, attention is also focussed on describing the versatility of LPME in its different possible formats and its ability to improve selectivity in the extraction of polar analytes with acid-base properties by using separation membranes and buffer solutions, instead of organic solvents, as the acceptor solution.

Keywords: Solid-phase microextraction; Liquid-phase microextraction; Single-drop microextraction; Membrane extraction; Stir-bar-sorptive extraction; Polar organic contaminants; Water analysis

Development of restricted-access media supports and their application to the direct analysis of biological fluid samples via high-performance liquid chromatography by N. M. Cassiano; V. V. Lima; R. V. Oliveira; A. C. de Pietro; Q. B. Cass (pp. 1462-1469).

A quick overview of published methods for analyzing compounds in complex biological samples reveals that the most difficult step is the clean-up or extraction of a required compound from the matrix. The strategy required to analyze exogenous compounds in biological fluids depends greatly upon the nature of the compound and upon the biomatrix. Coupled-column separation using restricted-access media as the first dimension in order to exclude macromolecules and retain micromolecules has been successfully used for a number of biological fluids. This paper presents the history of the development of restricted-access media supports and of their application to the direct injection of biological fluid samples in high-performance liquid chromatography.

Keywords: Restricted-access media (RAM); Direct injection; Column switching; Biological fluid samples

High-precision measurement of mercury isotope ratios in sediments using cold-vapor generation multi-collector inductively coupled plasma mass spectrometry by Delphine Foucher; Holger Hintelmann (pp. 1470-1478).

An on-line Hg reduction technique using stannous chloride as the reductant was applied for accurate and precise mercury isotope ratio determinations by multi-collector (MC)-ICP/MS. Special attention has been paid to ensure optimal conditions (such as acquisition time and mercury concentration) allowing precision measurements good enough to be able to significantly detect the anticipated small differences in Hg isotope ratios in nature. Typically, internal precision was better than 0.002% (1 RSE) on all Hg ratios investigated as long as approximately 20 ng of Hg was measured with a 10-min acquisition time. Introducing higher amounts of mercury (50 ng Hg) improved the internal precision to <0.001%. Instrumental mass bias was corrected using ²⁰⁵Tl/²⁰³Tl correction coupled to a standard-sample bracketing approach. The large number of data acquired allowed us to validate the consistency of our measurements over a one-year period. On average, the short-term uncertainty determined by repeated runs of NIST SRM 1641d Hg standard during a single day was <0.006% (1 RSD) for all isotope pairs investigated (²⁰²Hg/¹⁹⁸Hg, ²⁰²Hg/¹⁹⁹Hg, ²⁰²Hg/²⁰⁰Hg, and ²⁰²Hg/²⁰¹Hg). The precision fell to <0.01% if the long-term reproducibility, taken over 11 months (over 100 measurements), was considered. The extent of fractionation has been investigated in a series of sediments subject to various Hg sources from different locations worldwide. The ratio ²⁰²Hg/¹⁹⁸Hg expressed as δ values (per mil deviations relative to NIST SRM 1641d Hg standard solution) displayed differences from +0.74 to −4.00‰. The magnitude of the Hg fractionation per amu was constant within one type of sample and did not exceed 1.00‰. Considering all results (the reproducibility of Hg standard solutions, reference sediment samples, and the examination of natural samples), the analytical error of our δ values for the overall method was within ±0.28‰ (1 SD), which was an order of magnitude lower than the extent of fractionation (4.74‰) observed in sediments. This study confirmed that analytical techniques have reached a level of long-term precision and accuracy that is sufficiently sensitive to detect even small differences in Hg isotope ratios that occur within one type of samples (e.g., between different sediments) and so far have unequivocally shown that Hg isotope ratios in sediments vary within approximately 5‰.

Keywords: Mercury; Stable isotopes; Isotope ratios; Multi-collector ICP/MS; Fractionation; Sediments

Comprehensive two-dimensional capillary supercritical fluid chromatography in stop-flow mode with synchronized pressure programming by Yukio Hirata; Fujio Ozaki (pp. 1479-1484).

A comprehensive two-dimensional capillary supercritical fluid chromatography method was developed. The interface consisted of a ten-port valve, a capillary trap and two fused silica restrictors. The primary column was operated in stop-flow mode: the flow in the primary column was stopped during the separation of the second dimension. The pressure of the system was controlled with a single pump. The pressure program was synchronized with the sampling: the pressure was only ramped up during the sampling time, when the primary column effluent was transferred from the first dimension to the trap, and was maintained constant during the second-dimension separation. All of the operations were automated using in-house software. The separation characteristics of the present system can be readily regulated by changing the size of the restrictors and/or the programmed pressure rate. The use of synchronized pressure programming allowed the sampling duration and/or the second-dimension separation time (and therefore, the total analysis time) to be changed without affecting the separation pattern. Widely different selectivities were attained depending on the combination of the three columns with different polarities (such as the nonpolar DB-1, the medium-polarity DB-17 and the polar DB-WAX columns) used. The present system afforded improved separation and identification capabilities for analytes in complex mixtures.

Keywords: SFC (supercritical fluid chromatography); Capillary SFC; Comprehensive two-dimensional SFC; Stop-flow method; Synchronized pressure programming

Investigation of extraction procedures and HPLC-DAD/MS for the determination of the brominated flame retardant tetrabromobisphenol A bis(2,3-dibromopropylether) in environmental samples by Robert Köppen; Roland Becker; Christian Jung; Christian Piechotta; Irene Nehls (pp. 1485-1492).

A method for the determination of the novel brominated flame retardant tetrabromobisphenol A bis(2,3-dibromopropylether), 1,1′-(isopropylidene)bis[3,5-dibromo-4-(2,3-dibromo-propoxy)-benzene] (TBBPA-dbpe), was developed. Technical TBBPA-dbpe was purified and the results of a thorough physical characterisation are reported. The application of APCI-MS is discussed and the fragmentation patterns are described. Quantification of TBBPA-dbpe was done by HPLC-DAD using external calibration. The validation of the method was accomplished using sediment and sewage sludge samples spiked with defined amounts of authentic TBBPA-dbpe. The average recovery rates of TBBPA-dbpe from spiked samples ranged from 35 to 91% (sediment) and from 57 to 98% (sewage sludge) depending on the respective extraction method. Pressurised fluid extraction (PFE) and fluidised bed extraction were superior to classical Soxhlet and sonication procedures and yielded recovery rates between 90 and 98% with relative standard deviations of 2%. The limits of detection (DTC), identification (ID) and determination (DTM) using HPLC-DAD were 10, 21 and 30 ng g⁻¹ in sediment and 22, 44 and 72 ng g⁻¹ in sewage sludge, respectively.

Keywords: Extraction; TBBPA-dbpe; Sewage sludge; Sediment; LC-MS

Use of pseudo-sample extraction and the projection technique to estimate the chemical rank of three-way data arrays by Leqian Hu; Hailong Wu; Jianhui Jiang; Yujie Ding; Alin Xia; Ruqin Yu (pp. 1493-1500).

Determining the rank of a trilinear data array is a first step in subsequent trilinear component decomposition. Different from estimating the rank of bilinear data, it is more difficult to decide the significant number of component to fit the trilinear decompositions exactly. General methods of rank estimation utilize the information contained in the singular values but ignore information from eigenvectors. In this paper, a rank estimating method specifically for trilinear data arrays is proposed. It uses the idea of direct trilinear decomposition (DTLD) to compress the cube matrix into two pseudo sample matrices which are then decomposed by singular value decomposition. Two eigenvectors combined with the projection technique are used to estimate the rank of trilinear data arrays. Simulated trilinear data arrays with homoscedastic and heteroscedastic noise, different noise levels, high collinearity, and real three-way data arrays have been used to illustrate the feasibility of the proposed method. Compared with other factor-determining methods, for example use of the factor indication function (IND), residual percentage variance (RPV), and the two-mode subspace comparison approach (TMSC), the results showed that the new method can give more reliable answers under the different conditions applied.

Keywords: Rank estimation; Rank of three-way data arrays; Trilinear decomposition; Projection technique

Rapid and simultaneous determination of nonsteroidal anti-inflammatory drugs in human plasma by LC–MS with solid-phase extraction by Koichi Suenami; Lee Wah Lim; Toyohide Takeuchi; Yasuhide Sasajima; Kiyohito Sato; Yuji Takekoshi; Susumu Kanno (pp. 1501-1505).

A rapid, selective and sensitive analytical method for the simultaneous determination of 16 nonsteroidal anti-inflammatory drugs (NSAIDs) in human plasma was carried out using Oasis HLB solid-phase extraction (SPE), followed by reversed-phase high-performance liquid chromatography and quadrupole mass spectrometry with electrospray ionization operated in the negative ion mode. The recoveries of NSAIDs from human plasma by SPE were greater than 76.7%. The use of a short column packed with small particles enabled rapid and simultaneous determination within 7 min. The detection limits for the NSAIDs were 0.01–0.9 μg/ml using the selected ion monitoring mode.

Keywords: Nonsteroidal anti-inflammatory drugs; Liquid chromatography–mass spectrometry; Solid-phase extraction; Human plasma

Evaluation of CD detection in an HPLC system for analysis of DHEA and related steroids by A. Gergely; Gy. Szász; A. Szentesi; K. Gyimesi-Forrás; J. Kökösi; D. Szegvári; G. Veress (pp. 1506-1510).

The biological importance of dehydroepiandrosterone (DHEA) is reflected by the fact that DHEA is a crucial precursor of the biosynthesis of the steroidal sex hormones. Simultaneous separation of DHEA, dehydroepiandrosterone sulfate (DHEA-S), pregnenolone, androstenedione and testosterone has been accomplished by reversed-phase ion-pair high-performance liquid chromatography (RP-IP-HPLC) based on isocratic elution applying circular dichroism (CD) detection at 295 nm. Addition of tetrabutylammonium hydrogensulfate to the mobile phase increases the retention of DHEA-S on the C8-silica column by an apparent ion-pairing mechanism without affecting the retention of the other (non-ionic) steroids. CD spectroscopy provides highly selective detection of compounds possessing optically active absorption bands and the separation is even more selective in the higher wavelength range applied. The linearity of the steroid concentration (c, mg mL⁻¹) versus peak area was tested in the concentration range of 0.5–2 mg mL⁻¹ (injected quantities were 10–40 μg). The relative standard deviation (RSD) values for DHEA and DHEA-S indicated a good intra-assay and inter-assay precision of the method.

Keywords: DHEA; DHEA-S; Testosterone; Ion-pair chromatography; CD detection

Characterization and quantification of anthocyanins in selected artichoke (Cynara scolymus L.) cultivars by HPLC–DAD–ESI–MS n by Katrin Schütz; Markus Persike; Reinhold Carle; Andreas Schieber (pp. 1511-1517).

The anthocyanin pattern of artichoke heads (Cynara scolymus L.) has been investigated by high-performance liquid chromatography–electrospray ionization mass spectrometry. For this purpose a suitable extraction and liquid chromatographic method was developed. Besides the main anthocyanins—cyanidin 3,5-diglucoside, cyanidin 3-glucoside, cyanidin 3,5-malonyldiglucoside, cyanidin 3-(3′′-malonyl)glucoside, and cyanidin 3-(6′′-malonyl)glucoside—several minor compounds were identified. Among these, two peonidin derivatives and one delphinidin derivative were characterized on the basis of their fragmentation patterns. To the best of our knowledge this is the first report on anthocyanins in artichoke heads consisting of aglycones other than those of cyanidin. Quantification of individual compounds was performed by external calibration. Cyanidin 3-(6′′-malonyl)glucoside was found to be the major anthocyanin in all the samples analyzed. Total anthocyanin content ranged from 8.4 to 1,705.4 mg kg⁻¹ dry mass.

Keywords: Artichoke; Cynara scolymus L; Anthocyanins; HPLC–DAD–ESI–MS n

Colorimetric detection of immunoglobulin G by use of functionalized gold nanoparticles on polyethylenimine film by Haiqiu Li; Chungang Wang; Zhanfang Ma; Zhongmin Su (pp. 1518-1524).

A method based on use of functionalized gold nanoparticles on polyethylenimine film has been developed for colorimetric detection of immunoglobulin G (IgG). The immunogold nanoparticles were immobilized on quartz slides by recognition between antibody and antigen, with the antigen chemically adsorbed on the polyethylenimine film. By measurement of the UV–visible spectra of the immobilized immunogold, detection of h-IgG was achieved. The detection limit for h-IgG by use of this method can be as low as 0.01 μg mL⁻¹. This method is quite promising for numerous applications in immunoassay. Figure

Keywords: Immunoglobulin G; Gold nanoparticles; Polyethylenimine; Immunosensor

Influence of micelles on the electrochemical behaviors of catechol and hydroquinone and their simultaneous determination by Juan Peng; Zuo-Ning Gao (pp. 1525-1532).

A simple and highly selective electrochemical method for the simultaneous determination of CAT and HQ at a glassy carbon electrode in micellar solutions has been developed. The electrochemical behaviors of CAT and HQ in aqueous CPB and SDBS micellar solutions have been studied by cyclic voltammetry. The oxidation peak potentials shift negatively, the reduction peak potentials shift positively, and the peak currents increase in the presence of CPB for both CAT and HQ. However, the oxidation peak potentials shift positively, the reduction peak potentials shift negatively, and the peak currents decrease in the presence of SDBS for both CAT and HQ. The electrochemical kinetic parameters for CAT and HQ in aqueous CPB and SDBS micellar solutions were also determined by chronocoulometry (CC) and chronoamperometry (CA). The cyclic and pulse differential voltammetric behaviors of the system consisting of CAT coexisting with HQ were also investigated in this work. It was found that the oxidation peak potential waves of CAT and HQ were separated by 100 mV in the presence of CPB in 0.10 M PBS (pH 6.8). Therefore, CAT and HQ can be determined simultaneously in such a system. This simple method was applied to the simultaneous determination of HQ and CAT in a household tap water sample and it exhibited high selectivity.

Keywords: Micelle effects; Electrochemical behaviors; Catechol; Hydroquinone; Simultaneous determination

Separation and determination of honokiol and magnolol in herbal medicines by flow injection-capillary electrophoresis by Lihong Liu; Xinan Wu; Liuyin Fan; Xingguo Chen; Zhide Hu (pp. 1533-1539).

A simple, rapid, and accurate method for the separation and determination of honokiol and magnolol in Magnolia officinalis and related herbal medicines was developed by combination of flow injection (FI) and capillary zone electrophoresis (CZE). The analysis was carried out using an unmodified fused-silica capillary (50-μm I.D.; total length 7.5 cm; effective length 4.5 cm). A series of optimization steps afforded the following conditions: the sample solvent consisted of 150 mM NaOH and a running buffer composed of 10 mM sodium tetraborate/10 mM sodium dihydrogenphosphate (NaH₂PO₄) at pH 12 was applied for the separation of the analytes. The separation could be achieved within 5 min with a sample throughput rate of up to 28 h⁻¹. The repeatability (defined as the relative standard deviation, RSD) for honokiol and magnolol was 2.0% and 1.6% with peak area evaluation, 3.6% and 2.0% with peak height evaluation, and 2.0% and 1.4% with migration time evaluation, respectively. Regression equations revealed linear relationships (r = 0.9991–0.9998) between the peak area of each analyte and the concentration.

Keywords: Flow injection-capillary electrophoresis; Honokiol; Magnolol; Herbal medicines

Immunosensors for pollutants working in organic media. Study of performances of different tracers with luminescent detection by M. A. González-Martínez; J. Penalva; J. C. Rodríguez-Urbis; E. Brunet; A. Maquieira; R. Puchades (pp. 1540-1547).

A comparative study of enzymatic and non-enzymatic labels combined with luminescence detection, developed for immunosensing of pesticide residues (carbaryl, 1-naphthol, irgarol 1051) in organic media, is presented. Peroxidase and alkaline phosphatase enzymes with fluorogenic (3-p-hydroxyphenylpropanoic acid) and luminogenic (AMPPD derivative) substrates, respectively, were assessed as enzymatic markers. As an alternative, terbium(III) chelate, with time-resolved fluorescence detection, was evaluated as a non-enzymatic label. The best sensitivity was achieved by use of alkaline phosphatase in an immunocomplex capture assay format (I ₅₀ values 0.06, 0.27, and 7.45 μg L⁻¹ in buffer, 1:1 methanol–buffer, and methanol, respectively). Results were also good (I ₅₀ 1.00 and 6.30 μg L⁻¹ for water and aqueous–organic mixture, respectively) for Tb(III) chelate in an immobilized conjugate assay format. Use of alkaline phosphatase label to measure carbaryl (100 ng L⁻¹) in different spiked river water samples, after solid-phase extraction and analyte elution with an ethyl acetate–methanol mixture, resulted in recoveries ranging from 81 to 98%, with acceptable precision (CV 4–14%, n=4).

Keywords: Immunosensor; Organic media; Peroxidase; Alkaline phosphatase; Terbium(III) chelate; Time-resolved fluorescence detection

Further research on the photo-SPME of triclosan by Lucia Sánchez-Prado; Maria Llompart; Marta Lores; Maria Fernández-Álvarez; Carmen García-Jares; Rafael Cela (pp. 1548-1557).

In this study the photoinduced degradation of triclosan has been investigated by photo-solid-phase microextraction (photo-SPME). In photo-SPME, photodegradation is carried out on the SPME fibre containing the target compound. Triclosan was extracted from aqueous solutions by use of polydimethylsiloxane SPME fibres and these were subsequently exposed to UV irradiation (power 8 W, wavelength 254 nm) for different times (from 2 to 60 min). The photodegradation kinetics of triclosan were investigated, the photoproducts generated were tentatively identified, and the photochemical behaviour of these products was studied by use of this on-fibre approach followed by gas chromatographic–mass spectrometric analysis. Eight photoproducts were tentatively identified, including chlorinated phenols, chlorohydroxydiphenyl ethers, 2,8-dichlorodibenzo-p-dioxin, and a possible dichlorodibenzodioxin isomer or dichlorohydroxydibenzofuran. The main photodegradation mechanisms were postulated and photodegradation pathways proposed. The effect of pH on triclosan degradation and on triclosan-to-dioxin conversion was also investigated. Triclosan degradation occurred, and generation of 2,8-dichlorodibenzo-p-dioxin was confirmed, throughout the pH range studied (from 3 to 9).

Keywords: Photodegradation; Solid-phase microextraction; Photo-SPME; Triclosan; Dioxin; Chlorophenol

Cascade ultrafiltration and competing ligand exchange for kinetic speciation of aluminium, iron, and nickel in fresh water by Nouri M. Hassan; John D. Murimboh; Amina L. R. Sekaly; Rupasri Mandal; Chuni L. Chakrabarti; D. Conrad Grégoire (pp. 1558-1566).

Kinetic speciation of nickel, aluminium, and iron in fresh water has been investigated by cascade ultrafiltration followed by competing ligand exchange of the ultrafiltered fractions. Graphite furnace atomic absorption spectrometry was used to measure the kinetics of metal complex dissociation. Dissolved metal species were fractionated by cascade ultrafiltration. Metal speciation in each ultrafiltered fraction was then characterized as free metal ions, “labile” metal complexes (with dissociation rate constants ≥10⁻³ s⁻¹), “slowly labile” metal complexes (with dissociation rate constants >10⁻⁶ s⁻¹), and “inert” metal complexes (with dissociation rate constants <10⁻⁶ s⁻¹). The experimental results were compared with the predictions of a computer-based equilibrium speciation model, the Windermere humic aqueous model (WHAM) V. Cascade ultrafiltration coupled with kinetic speciation of the metal species in each molecular weight cut-off (MWCO) fraction provided a more comprehensive picture and insight into the physical and the chemical characteristics of the metal species than either ultrafiltration or measurement of dissociation kinetics alone.

Keywords: Chemical speciation; Kinetics; Cascade ultrafiltration; Metals; Fresh waters

Electrochemical properties of silver–copper alloy microelectrodes for use in voltammetric field apparatus by Silje M. Skogvold; Øyvind Mikkelsen; Gabriel Billon; Cedric Garnier; Ludovic Lesven; Jean-Francois Barthe (pp. 1567-1577).

Microelectrodes of silver–copper alloys have been evaluated for use in voltammetric analyses. Increased overpotential towards the hydrogen overvoltage reaction (HER) was found as a function of increased copper content in the silver. A study of oxidizing products by cyclic voltammetry (CV) in NaOH solution showed ten anodic and eight cathodic peaks which are described in the present paper. The behaviour of these alloy electrodes is somewhere between pure silver and pure copper electrodes. Differential pulse anodic stripping voltammetry (DPASV) was used to measure zinc, cadmium and lead in ultrapure water only (18 MΩcm), and good linearity was found for all metals (r ²=0.998) in the range of 0.5 to 5 ppb with a 600- to 1,200-s plating time. It was additionally found that cadmium and lead were better separated on the alloy electrodes compared to pure silver electrodes. Measurements of nickel were carried out on alloy electrodes by use of adsorptive differential pulse cathodic stripping voltammetry (Ad-DPCSV), and good linearity (r ²=1.000) was found in the range from 0.5 to 5 ppb with an adsorption time of 120 s. The alloy electrodes were also found to be sensitive to nitrate, and good linearity (r ²=0.997) was found in the range from 1 mg L⁻¹ to 100 mg L⁻¹ using differential pulse voltammetry (DPV) scanning from −450 mV to −1,500 mV. Addition of nitrate in ultrapure water afforded two different peaks related to the successive reductions of nitrate and nitrite. In ammonium buffer solution (pH 8.6) only one peak resulting from reduction of nitrate was observed. Furthermore, the use of alloy electrodes containing 17% Cu was tested in real samples, by installing it in a voltammetric system for monitoring of zinc and lead in a polluted river, the river Deûle, near the town of Douai in northern France. Results were found to be in agreement with parallel measurements carried out by ICP-MS.

Keywords: Voltammetry; Solid electrodes; Real samples

A novel droplet-tap sample-loading method for two-dimensional gel electrophoresis by X. -H. Long; J. -F. Lin; Y. -Z. Zhang (pp. 1578-1583).

A novel procedure, droplet-tap mode, has been devised for sample application for two-dimensional gel electrophoresis (2DE) expression profiles. The sample was loaded by evenly distributed tapping of droplets of the sample on to the rehydration buffer (RB) and then lowering the strip on to the solution surface. At normal loading concentrations, the number of spots obtained was increased by approximately one-third by this new approach compared with the rehydration loading procedure. The method also resulted in significantly improved resolution compared with cup loading when high concentrations of proteins were present, indicating its potential usefulness in micropreparative separation. In addition, recovery of the proteins confirmed that protein uptake was enhanced by use of this method. By enabling improved performances in 2DE, the proposed procedure has much potential for sample loading to meet the requirements of global proteome analysis.

Keywords: Two-dimensional gel electrophoresis; Sample-application method; Proteomics; Silkworm eggs

A novel headspace solid-phase microextraction method for the exact determination of organochlorine pesticides in environmental soil samples by Rusong Zhao; Xia Wang; Jinpeng Yuan; Ting Jiang; Shan Fu; Xiaobai Xu (pp. 1584-1589).

A novel method of determining organochlorine pesticides (OCPs) is described. It is based on solid-phase microextraction (SPME) and gas chromatography–electron capture detection. During the development of the method, soil samples were prepared, spiked with standard solution, and then aged for some time. Extraction conditions such as the extraction time, the NaCl content, the volume of water, the extraction temperature and the desorption time were investigated and optimized. The limits of detection obtained using the method ranged from 0.10 to 0.51 ng g⁻¹, and relative standard deviations were lower than 10% for most organochlorine pesticides. Real soil samples were successfully analyzed using the proposed method. The results from the method developed here were in good agreement with those obtained using ultrasonic extraction. The result demonstrates that aging soils spiked with standard solution is an important method development step, because the soil samples obtained using this approach are more like real soils than those obtained when aging is not used.

Keywords: Organochlorine pesticides; Solid-phase microextraction; Environmental soil samples; Gas chromatography–electron capture detector

A windowless flow cell-based miniaturized fluorescence detector for capillary flow systems by Jing Xu; Bing-Cheng Yang; Hong-Zhe Tian; Ya-Feng Guan (pp. 1590-1593).

A miniaturized fluorescence detector utilizing a three-dimensional windowless flow cell has been constructed and evaluated. The inlet and outlet liquid channels are collinear and are located in the same plane as the excitation paths, while the optical fiber used to collect the emission light is perpendicular to this plane. The straightforward arrangement of the flow path minimizes band dispersion and eliminates bubble formation or accumulation inside the cell. The use of high-brightness light-emitting diodes (LEDs) as the excitation source and a miniaturized metal package photomultiplier tube (PMT) results in a compact and sensitive fluorescence detector. The detection limit obtained from the system for fluorescein isothiocyanate (FITC) in flow injection mode is 2.6 nmol/L. The analysis of riboflavin and FITC by packed capillary liquid chromatography is demonstrated.

Keywords: Fluorescence detector; Windowless flow cell; Light-emitting diode; Capillary HPLC; Flow injection

Preservation procedures for arsenic speciation in a stream affected by acid mine drainage in southwestern Spain by Daniel Sánchez-Rodas; Vanesa Oliveira; Aguasanta M. Sarmiento; José Luis Gómez-Ariza; José Miguel Nieto (pp. 1594-1599).

A preservation study has been performed for arsenic speciation in surface freshwaters affected by acid mine drainage (AMD), a pollution source characterized by low pH and high metallic content. Two sample preservation procedures described in the literature were attempted using opaque glass containers and refrigeration: i) addition of 0.25 mol L⁻¹ EDTA to the samples, which maintained the stability of the arsenic species for 3 h; and ii) in situ sample clean-up with a cationic exchange resin, in order to reduce the metallic load, which resulted in a partial co-adsorption of arsenic onto Fe precipitates. A new proposed method was also tried: sample acidification with 6 mol L⁻¹ HCl followed by in situ clean-up with a cationic exchange resin, which allowed a longer preservation time of at least 48 h. The proposed method was successfully applied to water samples with high arsenic content, taken from the Aguas Agrias Stream (Odiel River Basin, SW Spain), which is severely affected by AMD that originates at the nearby polymetallic sulfide mine of Tharsis. The speciation results obtained by liquid chromatography–hydride generation–atomic fluorescence spectrometry (HPLC-HG-AFS) indicated that during the summer the main arsenic species was As(V) at the hundred μg L⁻¹ level, followed by DMA (dimethyl arsenic) and As(III) below the ten μg L⁻¹ level. In winter, As(V) and As(III) increased at least fivefold, whereas the DMA was not detected.

Keywords: Arsenic; Speciation; AMD; Sample preservation; Cationic exchange resin; EDTA; AFS

Determination of trace elements in suspensions and filtrates of drinking and surface water by wavelength-dispersive X-ray fluorescence spectrometry by Beata Zawisza; Rafał Sitko (pp. 1600-1604).

An X-ray fluorescence method (XRF) is presented that allowed low detection limits (at the 0.1–23 ng mL⁻¹ level) to be obtained for Cr, Mn, Fe, Ni, Zn, Sr, Pb, Bi and Br in water. The samples were prepared using a thin layer method. Trace elements were determined via the calibration curve and standard addition. Absorption effects and inhomogenities in prepared samples were checked for using the emission–transmission method and internal standards, respectively. The results from the XRF method were compared with the results from the inductively coupled plasma atomic emission spectrometry method.

Keywords: WDXRF; Water; Thin sample; Heavy metals; E–T method

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Analytical and Bioanalytical Chemistry (v.384, #7-8)