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Analytical and Bioanalytical Chemistry (v.381, #6)

Chelating sorbents based on silica gel and their application in atomic spectrometry by Mohammed Zougagh; J. M. Cano Pavón; A. Garcia de Torres (pp. 1103-1113).

This mini-review covers chelating sorbents anchored to silica gel and their analytical applications for the preconcentration, separation and determination of trace metal ions, focussing mainly on the last 20 years. The article summarizes also the experience gathered by our research group in the synthesis and characterization of new modified silica gels “via silanization”, and their affinity toward selective extraction and separation of trace elements. The introduction of 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-gel) and methylthiosalicylate silica gel (TS-gel) chelating sorbents in trace and ultratrace analysis provide vital breakthroughs in preconcentration methods. These home-made materials allow certain analytes to be selectively extracted from complex matrices without matrix interference and good detection limits. The advantages of these new chelating sorbents in comparison with 8-hydroxyquinoline chelating sorbent immobilized on silica gel are discussed.

Keywords: Chelating sorbents; Silica gel; DPTH-gel; TS-gel; Sorbent materials

Escherichia coli single-strand binding protein–DNA interactions on carbon nanotube-modified electrodes from a label-free electrochemical hybridization sensor by Kagan Kerman; Yasutaka Morita; Yuzuru Takamura; Eiichi Tamiya (pp. 1114-1121).

An electrochemical hybridization biosensor based on the intrinsic oxidation signals of nucleic acids and proteins has been designed, that makes use of the unique binding event between Escherichia coli single-strand binding protein (SSB) and single-stranded DNA (ssDNA). The voltammetric signal from guanine oxidation significantly decreased upon binding of SSB to single-stranded oligonucleotides (probe), anchored on a single-walled carbon nanotube (SWCNT) -modified screen-printed carbon electrode (SPE). Simultaneously, oxidation of the tyrosine (Tyr) and tryptophan (Trp) residues of the SSB protein increased upon binding of the SSB protein to ssDNA and ss-oligonucleotides. After the hybridization, SSB did not bind to the double helix form, and the guanine signal could be observed along with the disappearance of the oxidation signal of the protein. The amplification of intrinsic guanine and protein oxidation signals by SWCNT, and a washing step with sodium dodecylsulfate, enabled the specific detection of a point mutation. Monitoring the changes in the guanine and protein signals upon hybridization greatly simplified the detection procedure. The detection limit of 0.15 μg/ml target DNA can be applied to genetic assays. To the best of our knowledge, this is the first work that utilizes the monitoring of SSB–DNA interactions on a solid transducer for the electrochemical detection of DNA hybridization by using intrinsic oxidation signals.

Keywords: Electrochemical DNA sensor; DNA hybridization; Guanine oxidation; Protein oxidation; Single-strand binding protein

Optical detection and discrimination of cystic fibrosis-related genetic mutations using oligonucleotide–nanoparticle conjugates by Deirdre Murphy; Gareth Redmond (pp. 1122-1129).

Novel methods for application of oligonucleotide–gold nanoparticle conjugates to selective colorimetric detection and discrimination of cystic fibrosis (CF) related genetic mutations in model oligonucleotide systems are presented. Three-strand oligonucleotide complexes are employed, wherein two probe oligonucleotide–gold nanoparticle conjugates are linked together by a third target oligonucleotide strand bearing the CF-related mutation(s). By monitoring the temperature dependence of the optical properties of the complexes, either in solution or on silica gel plates, melting behaviors may be accurately and reproducibly compared. Using this approach, fully complementary sequences are successfully distinguished from mismatched sequences, with single base mismatch resolution, for Δ F 508, M470V, R74W and R75Q mutations.

Keywords: Cystic fibrosis; Oligonucleotide–nanoparticle conjugate; Optical melting curve; Mutation detection

Reductive amination of carbohydrates using NaBH(OAc)₃ by Dilusha S. Dalpathado; Hui Jiang; Marcus A. Kater; Heather Desaire (pp. 1130-1137).

An improved protocol for reductive amination of carbohydrates is developed. This derivatization facilitates the detection of oligosaccharides in HPLC-UV and mass spectrometric applications by enhancing the signal of the carbohydrates. In this study, reductive amination was achieved using NaBH(OAc)₃.This reducing agent is an attractive alternative to the toxic, but extensively used reducing agent, NaBH₃CN. Several types of carbohydrates were successfully derivatized using NaBH(OAc)₃, and the results obtained from this protocol were compared with those obtained with NaBH₃CN. Both reducing agents were equally effective in side-by-side analysis. Two purification strategies (purification by zip-tip and HPLC) were implemented and the instrumental limit of detection of each method was compared. The detection limit was ~1,000 times lower when the purification was done using HPLC, compared to using the zip-tip. Since the derivatization by-products in this protocol are not toxic, MS analysis also could also be performed directly, without purification. The MS/MS data of derivatized and underivatized oligosaccharides were acquired as well. The derivatized oligosaccharides produce more easily interpretable product ions than underivatized oligosaccharides.

Keywords: Carbohydrates; Oligosaccharides; Reductive amination; Mass spectrometry; NaBH(OAc)3; Derivatization

New application of a subcellular fractionation method to kidney and testis for the determination of conjugated linoleic acid in selected cell organelles of healthy and cancerous human tissues by Kristina Hoffmann; Jörg Blaudszun; Claus Brunken; Wilhelm-Wolfgang Höpker; Roland Tauber; Hans Steinhart (pp. 1138-1144).

To clarify the mechanism of the anticarcinogenic effect of conjugated linoleic acid (CLA), its intracellular distribution needs to be determined. Subcellular fractionation using centrifugation techniques is a method that is frequently used for isolation of cell organelles from different tissues. But as the size and density of the organelles differ, the method needs to be optimised for every type of tissue. The novelty of this study is the application of a subcellular fractionation method to human healthy and cancerous renal and testicular tissue. Separation of total tissue homogenate into nuclei, cytosol, and a mixture of mitochondria and plasma membranes was achieved by differential centrifugation. As mitochondria and plasma membranes seemed to be too similar in size and weight to be separated by differential centrifugation, discontinuous density-gradient centrifugation was carried out successfully. The purity of the subcellular fractions was checked by measuring the activity of marker enzymes. All fractions were highly enriched in their corresponding marker enzyme. However, the nuclear fractions of kidney and renal cell carcinoma were slightly contaminated with mitochondria and plasma membrane fractions of all tissues with lysosomes. The fraction designated the cytosolic fraction contained not only cytosol, but also microsomes and lysosomes. The CLA contents of the subcellular fractions were in the range 0.13–0.37% of total fatty acids and were lowest in the plasma membrane fractions of all types of tissue studied. C16:0, C18:0, C18:1 c9, C18:2 n-6, and C20:4 n-6 were found to be the major fatty acids in all the subcellular fractions studied. However, marked variations in fatty acid content between subcellular fractions and between types of tissue were detectable. Because of these differences between tissues, no general statement on characteristic fatty acid profiles of single subcellular fractions is possible.

Keywords: CLA; Subcellular fractionation; Kidney; Renal cell carcinoma; Testis; Testicular carcinoma

Determination of total selenium and selenium distribution in the milk phases in commercial cow’s milk by HG-AAS by Óscar Muñiz-Naveiro; Raquel Domínguez-González; Adela Bermejo-Barrera; José A. Cocho; José M. Fraga; Pilar Bermejo-Barrera (pp. 1145-1151).

A procedure has been developed for determining the selenium in cow’s milk using hydride generation–atomic absorption spectrometry (HG-AAS) following microwave-assisted acid digestion. The selenium distributions in milk whey, fat and micellar casein phases were studied after separating the different phases by ultracentrifugation and determining the selenium in all of them. The detection limits obtained by HG-AAS for the whole milk, milk whey and micellar casein were 0.074, 0.065 and 0.075 μg l⁻¹, respectively. The accuracy for the whole milk was checked by using a Certified Reference Material CRM 8435 whole milk powder from NIST, and the analytical recoveries for the milk whey and casein micelles were 100.9 and 96.9%, respectively. A mass balance study of the determination of selenium in the different milk phases was carried out, obtaining values of 95.5–100.8%. The total content of selenium was determined in 37 milk samples from 15 different manufacturers, 19 whole milk samples and 18 skimmed milk samples. The selenium levels found were within the 8.5–21 μg l⁻¹ range. The selenium distributions in the different milk phases were studied in 14 whole milk samples, and the highest selenium levels were found in milk whey (47.2–73.6%), while the lowest level was found for the fat phase (4.8–16.2%). A strong correlation was found between the selenium levels in whole milk and the selenium levels in the milk components.

Keywords: Selenium; Whole milk; Milk whey; Fat milk; Casein micelles; Microwave-assisted acid digestion; Hydride generation–atomic absorption spectrometry

Sandwich immunoassay for determination of vitellogenin in golden grey mullet (Liza aurata) serum as a field exposure biomarker by Juan F. Asturiano; Francisco Romaguera; Pilar Aragón; Julia Atienza; Rosa Puchades; Ángel Maquieira (pp. 1152-1160).

Vitellogenin (VTG) is a protein produced in the liver of oviparous animals in response to oestrogens. Abnormal production of VTG by males, therefore, is used as a biological indicator of exposure to xeno-oestrogens. In this study, a sandwich-ELISA for measuring VTG in Liza aurata (golden grey mullet) was developed and validated. Plasma VTG was purified from 17β-oestradiol-injected immature individuals of mullet, by size-exclusion and ion-exchange chromatography. Polyclonal antibodies against VTG were raised in rabbits. A sensitive immunoassay was developed for measurement of vitellogenin in L. aurata serum, reaching a quantification limit of 0.01 μg mL⁻¹ and a dynamic range from 0.02 to 2 μg mL⁻¹. The assay is specific, because high levels (>100 μg mL⁻¹) of carp (Cyprinus carpio), goldfish (Carassius auratus), tilapia (Oreochromis niloticus), tench (Tinca tinca), rainbow trout (Oncorhynchus mykiss), European eel (Anguilla anguilla) and frog (Rana perezi) purified VTG, give negligible responses. The assay was used to analyse plasma samples from wild mullet.

Keywords: Endocrine-disrupting compounds; Vitellogenin; Immunoassay; Liza aurata; Mullet; Biomarker

Determination of dopamine in synthetic cerebrospinal fluid by SWV with a graphite–polyurethane composite electrode by R. A. de Toledo; M. C. Santos; E. T. G. Cavalheiro; L. H. Mazo (pp. 1161-1166).

This work describes an electroanalytical investigation of dopamine using cyclic voltammetry (CV) and the graphite–polyurethane composite electrode (GPU). In CV studies, well-defined redox peaks characterize the oxidation process at the GPU electrode, which is indicative of electrocatalytic effects associated with active sites on the GPU electrode surface. A new analytical methodology was developed using the GPU electrode and square wave voltammetry (SWV) in BR buffer solution (0.1 mol L⁻¹; pH 7.4). Analytical curves were constructed under optimized conditions (f=60s⁻¹, ΔE_a=50 mV, ΔE_I=2 mV) and detection and quantification limits of 6.4×10⁻⁸ mol L⁻¹ (12.1 μg L⁻¹) and 5.2×10⁻⁶ mol L⁻¹ (0.9 mg L⁻¹), respectively, were achieved. The precision of the method was checked by performing ten successive measurements for a 9.9×10⁻⁶ mol L⁻¹ dopamine solution. For intra-assay and inter-assay precisions, the relative standard deviations were 1.9 and 2.3%, respectively. In order to evaluate the developed methodology, the determination of dopamine was performed with good sensitivity and selectivity, without the interference of ascorbic acid in synthetic cerebrospinal fluid, which indicates that the new methodology enables reliable analysis of dopamine.

Keywords: Dopamine; Electrochemical oxidation; Analytical determination; Graphite–polyurethane composite electrode; Synthetic cerebrospinal fluid

An analysis of avidin, biotin and their interaction at attomole levels by voltammetric and chromatographic techniques by Rene Kizek; Michal Masarik; Karl J. Kramer; David Potesil; Michele Bailey; John A. Howard; Borivoj Klejdus; Radka Mikelova; Vojtech Adam; Libuse Trnkova; Frantisek Jelen (pp. 1167-1178).

The electroanalytical determination of avidin in solution, in a carbon paste, and in a transgenic maize extract was performed in acidic medium at a carbon paste electrode (CPE). The oxidative voltammetric signal resulting from the presence of tyrosine and tryptophan in avidin was observed using square-wave voltammetry. The process could be used to determine avidin concentrations up to 3 fM (100 amol in 3 μl drop) in solution, 700 fM (174 fmol in 250 μl solution) in an avidin-modified electrode, and 174 nM in a maize seed extract. In the case of the avidin-modified CPE, several parameters were studied in order to optimize the measurements, such as electrode accumulation time, composition of the avidin-modified CPE, and the elution time of avidin. In addition, the avidin-modified electrode was used to detect biotin in solution (the detection limit was 7.6 pmol in a 6 μl drop) and to detect biotin in a pharmaceutical drug after various solvent extraction procedures. Comparable studies for the detection of biotin were developed using HPLC with diode array detection (HPLC-DAD) and flow injection analysis with electrochemical detection, which allowed biotin to be detected at levels as low as 614 pM and 6.6 nM, respectively. The effects of applied potential, acetonitrile content, and flow rate of the mobile phase on the FIA-ED signal were also studied.

Keywords: Avidin; Biotin; Avidin–biotin technology; Square-wave voltammetry; Modified electrode; High-performance liquid chromatography; Diode array detection; Electrochemical transfer technique; Carbon paste electrode; Drug analysis

Hydrogen peroxide sensor based on horseradish peroxidase immobilized on a silver nanoparticles/cysteamine/gold electrode by Chunbo Ren; Yonghai Song; Zhuang Li; Guoyi Zhu (pp. 1179-1185).

A third-generation hydrogen peroxide biosensor was prepared by immobilizing horseradish peroxidase (HRP) on a gold electrode modified with silver nanoparticles. A freshly-cleaned gold electrode was first immersed in a cysteamine–ethanol solution, and then silver nanoparticles were immobilized on the cysteamine monolayer, and finally HRP was adsorbed onto the surfaces of the silver nanoparticles. This self-assemble process was examined via atomic force microscopy (AFM). The immobilized horseradish peroxidase exhibited an excellent electrocatalytic response toward the reduction of hydrogen peroxide. The linear range of the biosensor was 3.3 μM to 9.4 mM, and the detection limit was estimated to be 0.78 μM. Moreover, the biosensor exhibited a fast response, high sensitivity, good reproducibility, and long-term stability.

Keywords: Biosensor; Horseradish peroxidase; Self-assemble; Silver nanoparticles; AFM

Perchlorate-selective membrane electrode based on a new complex of uranil by M. Mazloum Ardakani; M. Jalayer; H. Naeimi; H. R. Zare; L. Moradi (pp. 1186-1192).

A potentiometric ion-selective electrode based on new compound, as a carrier, has been successfully developed for detection of perchlorate anion in aqueous solution. Within the perchlorate ion concentration range 1.0×10⁻⁶ to 1.0 mol L⁻¹ the electrode had a linear response with a Nernstian slope of 60.6±1.0 mV per decade . The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration plot was 8.0×10⁻⁷ mol L⁻¹. The proposed electrode has fairly a good discriminating ability towards ClO₄⁻ ion in comparison to other anions. The sensor has a response time of ≤10 s and can be used for at least 2 months without substantial divergence in potential. It was successfully applied to direct determination of perchlorate in urine and water.

Keywords: Perchlorate-selective electrode; Potentiometry; PVC membrane; Ion-selective electrodes (ISEs); 2,2′-[1,2-ethanediyl-bis(nitriloethylidine)]-bis-phenolato uranil (UO₂L)

LC/MS determination of bisphenol A in river water using a surface-modified molecularly-imprinted polymer as an on-line pretreatment device by Yoshiyuki Watabe; Ken Hosoya; Nobuo Tanaka; Takuya Kondo; Masatoshi Morita; Takuya Kubo (pp. 1193-1198).

A new analytical method for the determination of bisphenol A (BPA) by LC/MS was developed and applied to environmental water samples. Quantitative MS detection of BPA was carried out in the negative mode. In order to preconcentrate the target compound yet prevent serious contamination of the water samples from the experimental environment, we employed column switching HPLC coupled with a pretreatment column of surface-modified molecularly-imprinted polymers. The recovery of BPA from a spiked environmental water sample was 102% and the repeatability of actual determinations of water samples containing 20 ng/L of BPA was 5.4% RSD. By modifying the surfaces of the molecularly-imprinted polymer particles packed in the pretreatment column, interference from the water samples was effectively removed, resulting in a significant increase in sensitivity and more reliable results. This method was successfully applied to the trace determination of BPA in environmental water samples using LC/MS.

Keywords: Water analysis; Molecular imprinting; Column switching; Endocrine disruptor; Bisphenol A; Pretreatment; LC/MS

Development of an analytical procedure for determination of selected estrogens and progestagens in water samples by Pierre Labadie; Hélène Budzinski (pp. 1199-1205).

An analytical procedure has been developed for determination of eight selected natural and synthetic hormonal steroids in surface water and in effluent samples. Several methodological points have been investigated and are discussed; they include the choice of the solid-phase extraction sorbent, the influence of flow rate on recovery, the breakthrough volume for a given sorbent (Env+ and Oasis HLB), sample clean up, and sample storage. As regards the latter point, it was found that when no preservative was added to effluent from a sewage-treatment plant, severe loss of steroids occurred—85% of progesterone and about 30% of both estrone and estradiol were found to be degraded in 24 h. The procedure developed was applied to samples from the Seine river estuary. Sex steroids were not detected in surface water; estrone was the most commonly detected steroid in sewage-treatment plant effluent, with levels ranging from 1.8 to 8.3 ng L⁻¹. Synthetic estrogens (ethynylestradiol and mestranol) and progestagens (levonorgestrel and norethindrone) were never detected, whatever the sampling season. Overall, for 162 out of 168 measurements levels were below the detection limits of the developed procedure.

Keywords: Estrogens; Progestagens; Solid-phase extraction; Sewage; Surface water

Ultrasound-assisted extraction and on-line LC–GC–MS for determination of polycyclic aromatic hydrocarbons (PAH) in urban dust and diesel particulate matter by Anders Christensen; Conny Östman; Roger Westerholm (pp. 1206-1216).

A method has been developed for determination of polycyclic aromatic hydrocarbons (PAH) in particulate matter from ambient air and diesel exhaust emissions. It is reproducible and accurate and, compared with similar methods for analysis of individual PAH components in complex matrices, it is relatively fast and simple. Single PAH components can be determined in samples of particulate matter from ambient air and diesel exhaust emissions with LOD of approximately 1 pg/sample. Further, sample throughput is high, because more than 20 samples can be extracted and prepared for analysis in one working (8-h) day. The particulate matter is subjected to ultrasound-assisted extraction, a technique that is shown to extract PAH from particulate material with efficiencies fully comparable with those of Soxhlet extraction. An aliphatic/PAH-enriched fraction is obtained by solid-phase extraction before isolation, separation, and identification/quantification of PAH by on-line liquid chromatography–gas chromatography–mass spectrometry. The method was validated by analysis of US National Institute of Standards and Technology (NIST) Standard Reference Materials (SRM) 1649a, Urban Dust, and 2975, Diesel Particulate Matter. Results from the method are in good agreement with the NIST-certified PAH concentrations and with NIST reference PAH concentrations.

Keywords: PAH; SRM 1649a; SRM 2975; LC; GC; MS; Particle analysis; PTV

Application of coupled-column liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection to the determination of pyrethroid insecticides in vegetable samples by P. Parrilla Vázquez; M. D. Gil García; D. Barranco Martínez; M. Martínez Galera (pp. 1217-1225).

This study reports the first application of coupled-column liquid chromatography–photochemically induced fluorimetry–fluorescence detection (LC-LC-PIF-FD), demonstrating its potential for the quantitative and selective detection of seven pyrethroids in vegetable samples such as cucumber, green bean, tomato and aubergine. An internal surface reversed-phase (ISRP) column coupled to a C₁₈ column for analyte clean-up and determination were used, respectively. In comparison with a C₁₈ column, the ISRP substantially improved the separation between analytes and interferences from the vegetable matrix. The limits of detection ranged from 0.01 to 0.22 μg kg⁻¹ in the vegetable samples (equivalent to 0.01 and 0.13 μg L⁻¹ in the extract injected), and limits of determination ranged from 0.56 to 8.33 μg kg⁻¹ in the vegetable samples (equivalent to 0.34 and 5.00 μg L⁻¹ in the extract injected). Samples were extracted into dichloromethane to yield mean recoveries at two levels of concentration between 72.8 and 110.0% in all cases. Relative standard deviations were lower than 11%.

Keywords: LC-LC; Photochemically induced fluorescence; Clean-up; Vegetables; Pyrethroids

A multiresidue method using ion-trap gas chromatography–tandem mass spectrometry with or without derivatisation with pentafluorobenzylbromide for the analysis of pesticides in the atmosphere by Anne Scheyer; Stéphane Morville; Philippe Mirabel; Maurice Millet (pp. 1226-1233).

A multiresidue method using gas chromatography coupled to ion-trap tandem mass spectrometry (MS/MS) was developed for the analysis of 27 pesticides, commonly used in Alsace, in atmospheric samples (particle and gas phases). As pesticides are expected to be present at very low concentrations and in a complex matrix, the analytical method used was both highly selective and sensitive. These two properties were obtained by associating chromatography with ion-trap MS/MS. To develop this method, analysis of electron impact in single MS was first conducted to choose the parent ions of the pesticides studied. Among the 27 pesticides analysed, seven of them require a derivatisation step. This was the case of some ureas (chlorotoluron, diuron and isoproturon), phenoxy acids (2,4-dichlorophenoxyacetic acid, 4-chloro-2-methylphenoxyacetic acid and mecoprop) and of bromoxynil. The derivatisation was performed with success with pentafluorobenzylbromide. Then, a MS/MS method was optimised by parameters such as the radio frequency storage level and the collision-induced dissociation excitation voltage. Finally, a last step enabled the development of two calibrating programs based on the quantification of daughter ions for the 20 pesticides analysed directly (run 1) and for the seven pesticides which needed derivatisation (run 2). With this analytical procedure, the detection limits varied between 2.5 and 1,250 pg m⁻³ depending on the compounds studied. This method was tested with success for atmospheric samples collected in Strasbourg (France) during intensive pesticide treatment in 2002.

Keywords: Pesticides; Atmosphere; Gas chromatography–tandem mass spectrometry; Derivatisation with pentafluorobenzylbromide

Clean up of phenylurea herbicides in plant sample extracts using molecularly imprinted polymers by F. G. Tamayo; J. L. Casillas; A. Martin-Esteban (pp. 1234-1240).

Two different molecularly imprinted polymers (MIPs) were prepared by precipitation polymerization using linuron or isoproturon (phenylurea herbicides) as templates and trifluormethacrylic acid as functional monomer. These materials were used as selective sorbents in the development of molecularly imprinted solid-phase extraction (MISPE) procedures for the determination of several phenylurea herbicides (fenuron, metoxuron, chlortoluron, isoproturon, metobromuron, and linuron) in plant samples extracts. The MISPE procedures were fully optimized and applied to the clean up of selected phenylurea herbicides in carrot, potato, corn, and pea sample extracts and finally determined by HPLC-UV at 244 nm. Although a high degree of clean up was obtained, a decrease of the MIP recognition capabilities was observed in subsequent runs. Thus, a previous clean up protocol based on the use of a non-imprinted polymer was used to prevent the loss of MIP performance and to ease the removal of interferences. Following this procedure, namely two-step MISPE, matrix compounds were almost completely removed by the non-imprinted polymer retaining the ability of MIPs to selectively rebind target analytes unaltered. The developed MISPE procedures allowed the screening of phenylurea herbicides in plant samples at concentration levels required by established European maximum residue limits.

Keywords: Imprinted polymers; Precipitation polymerization; Phenylurea herbicides; Molecularly imprinted solid-phase extraction

Chemotaxonomy of aromatic plants of the genus Origanum via vibrational spectroscopy by M. Baranska; H. Schulz; H. Krüger; R. Quilitzsch (pp. 1241-1247).

Fourier transformed-Raman (FT-Raman) and attenuated total reflection-infrared (ATR-IR) spectra of essential oils obtained from marjoram and oregano plants by hydrodistillation are presented. It is shown that the main components of the essential oils can be ascertained through both of these complementary techniques, using spectral information from the pure terpenoids. Spectroscopic analysis is based on the characteristic key bands of the individual volatile substances and therefore, in principle, these techniques allow us to discriminate between different essential oil profiles from individual oil plants of the same species (chemotypes). The combination of vibrational spectroscopy and hierarchical cluster analysis provides a fast, easy and reliable method for chemotaxonomy characterisation. The spectroscopic data presented here correlate very well with those found by gas chromatography (GC) analysis.

Keywords: Essential oil; Marjoram; Oregano; NIR-FT-Raman; ATR-IR; Hierarchical cluster analysis

Ultrasonic extraction followed by sulfuric acid silica gel cleanup for the determination of α-hexachlorocyclohexane enantiomers in biota samples by Rusong Zhao; Shaogang Chu; Rongbiao Zhao; Xiaobai Xu; Xiufen Liu (pp. 1248-1252).

Interest in the analysis of α-hexachlorocyclohexane (α-HCH) enantiomers as an alternative or complementary approach to elucidating isomer ratios of α/γ-HCH has grown in recent years because it can provide useful information to evaluate the influence of different degradation and transformation processes. In this paper, a simple and rapid method for the determination of α-HCH enantiomers in biota samples is described. The method developed consists of ultrasonic extraction, sulfuric acid silica gel cleanup, solid-phase extraction (SPE) column fractionation, and final determination with chiral high-resolution gas chromatography. Ultrasonic extraction greatly shortens the extraction process time, and the sulfuric acid silica gel and SPE cleanup perfectly remove lipids and other interference compounds in the lipid-rich samples. The method is found to be simple, less time-consuming, and easy to operate, thus providing a useful alternative method to assess the enantioselective breakdown of α-HCH in biota system.

Keywords: α-HCH; Biota analysis; Ultrasonic extraction; Sulfuric acid silica gel; Chiral analysis

A novel approach for the determination of detection limits for metal analysis of environmental water samples by X Jin Yang; Gary K-C Low; Roy Foley (pp. 1253-1263).

Despite the widespread use of the USEPA method (U.S. Environmental Protection Agency, 40 CFR 136 Appendix B) for the determination of method detection limit (MDL), criticisms have been raised that the method does not account for measurement bias and outliers that subsequently lead to a common misunderstanding of the requirement for the determination of MDL. This paper demonstrates that it is difficult to follow the USEPA method for verifying the MDL for analysis involving multiple metals and proposes a precision and bias criterion for determining the MDL. A multiple-point fitted profile, based on the correlation between relative standard deviation (RSD) and concentration, is used to derive a robust MDL value. Representative examples of As, Ca, Cr, and Cu are used to illustrate this procedure. A procedure for identifying outliers is also discussed.

Keywords: Method detection limit; Metals; Environmental samples

Simultaneous determination of DTPA, EDTA, and NTA by capillary electrophoresis after complexation with copper by Pirkko-Leena Laamanen; Antti Mali; Rose Matilainen (pp. 1264-1271).

We present a method for simultaneous determination of the aminopolycarboxylic acids DTPA, EDTA and NTA in dishwashing detergents, paper mill waters, and natural waters by capillary electrophoresis (CE). The complexing agents were examined as their copper(II) complexes and separated by conventional CE with reversed polarity of the applied voltage. The optimum separation conditions were established by varying the pH and phosphate and tetradecyltrimethylammonium bromide (TTAB) concentrations in the run buffer. The separations were carried out in a fused-silica capillary (61 cm×75 μm i.d.) filled with phosphate buffer (80 mmol L⁻¹, TTAB concentration 0.5 mmol L⁻¹, pH 7.1, voltage −20 kV) using direct UV detection at 191 and 254 nm. With this CE method all the peaks in the electropherograms were properly separated, the calibration plots gave good correlation coefficients and all three complexing agents could be detected in less than 4 min. Linear calibration plots were obtained for CuDTPA, CuEDTA and CuNTA; limits of detection were 0.03 mmol L⁻¹ for all complexing agents and recoveries for all tested samples were within the range 104±7%. Results obtained from dishwashing detergent samples were found to be reliable and comparable with those from HPLC (R²=0.989) and UV–Vis (R²=0.985) methods.

Keywords: Capillary electrophoresis; DTPA; EDTA; NTA; Dishwashing detergents

Organotin analysis by gas chromatography–pulsed flame-photometric detection (GC–PFPD) by M. Leermakers; J. Nuyttens; W. Baeyens (pp. 1272-1280).

Monobutyltin (MBuT), dibutyltin (DBuT), and tributyltin (TBuT) mixtures have been separated and quantified by gas chromatography with pulsed flame-photometric detection (GC–PFPD). The compounds were first derivatized with NaBEt₄, then extracted with hexane and injected into the GC in splitless mode. Optimum GC and detector conditions were established. For GC, various injector temperatures and oven temperature programs were tested. For the PFPD detector, gate settings (gate delay and gate width) and detector temperature were optimized. A very good linearity was obtained up to 100–150 ppb for all organotin compounds. The detection limits obtained were: MBuT (0.7 ppb), DBuT (0.8 ppb), and TBuT (0.6 ppb). RSD for repeatability and reproducibility were well below 20% when the instrument was in routine operation. A biological sample (CRM 477) was also analyzed for organotins. Extraction from the biological matrix was performed with TMAH. Besides the increased risk of contamination, the derivatization step seemed to be critical. pH and amount of derivatizing agent were tested. When using an internal standard (TPrT) between 90% and 110% of the certified amounts of organotin were recovered.

Keywords: Organotin; Analysis; Gas chromatography; Pulsed flame-photometric detection; Water; Biota

Fluorescence analysis of humic and fulvic acids from two Brazilian oxisols as affected by biosolid amendment by E. I. Bertoncini; V. D’Orazio; N. Senesi; M. E. Mattiazzo (pp. 1281-1288).

Conventional monodimensional fluorescence spectroscopy in the emission, excitation, and synchronous-scan modes and total luminescence spectroscopy have proven to be sensitive techniques for characterization and differentiation of humic acid (HA) and fulvic acid (FA) fractions isolated from an aerobically and anaerobically digested and limed biosolid, two layers of a sandy and a clayey Brazilian oxisol, and the corresponding biosolid-amended soils. The spectral patterns and the relative fluorescence intensities suggest greater molecular heterogeneity, less aromatic polycondensation, and less humification of biosolid HA and FA compared with soil HA and FA. However, the differences are smaller for the FA fractions than for the HA fractions. Fluorescence properties of soil HA and FA differ slightly as a function of soil type and soil layer. Biosolid application causes a shift to shorter wavelengths of the main fluorescence peaks and marked variation of the relative fluorescence intensities of HA and FA isolated from amended soils. These results suggest that molecular components of relatively small molecular size, with a low level of aromatic polycondensation, and low degree of humification present in biosolid HA and FA are partially and variously incorporated into amended soil HA and FA. In general, these modifications seem to be smaller in HA and FA from the clayey soil layers than in those from the sandy soil layers, possibly because of protective effects exerted by clay minerals of native soil HA and FA against disturbances caused by biosolid application.

Keywords: Biosolid; Oxisols; Humic acids; Fulvic acids; Monodimensional fluorescence spectroscopy; Total luminescence spectroscopy

Quantitative analysis of hydrogen peroxide by ¹H NMR spectroscopy by Ned A. Stephenson; Alexis T. Bell (pp. 1289-1293).

A technique utilizing ¹H NMR spectroscopy has been developed to measure the concentration of hydrogen peroxide from 10⁻³ to 10 M. Hydrogen peroxide produces a peak at around 10–11 ppm, depending upon the interaction between solvent molecules and hydrogen peroxide molecules. The intensity of this peak can be monitored once every 30 s, enabling the measurement of changes in hydrogen peroxide concentration as a function of time. ¹H NMR has several advantages over other techniques: (1) applicability to a broad range of solvents, (2) ability to quantify hydrogen peroxide rapidly, and (3) ability to follow reactions forming and/or consuming hydrogen peroxide as a function of time. As an example, this analytical technique has been used to measure the concentration of hydrogen peroxide as a function of time in a study of hydrogen peroxide decomposition catalyzed by iron(III) tetrakispentafluorophenyl porphyrin.

Keywords: Hydrogen peroxide; Proton NMR; Quantification analysis

Confirmation of the formation of dichlorodibenzo-p-dioxin in the photodegradation of triclosan by photo-SPME by Marta Lores; Maria Llompart; Lucia Sanchez-Prado; Carmen Garcia-Jares; Rafael Cela (pp. 1294-1298).

Photodegradation is a possible way to eliminate organic pollutants from the environment but, at the same time, can be a source of toxic byproducts. The photochemical conversion of triclosan, a common pollutant in continental waters, into dichlorodibenzo-p-dioxin (DCDD) has been confirmed in our preliminary experiments employing photo-SPME (photo-solid-phase microextraction) using 18-W UV irradiation at 254-nm wavelength. Under these conditions, triclosan is rapidly photodegraded (70% of triclosan was degraded in 2 min); the most important novel aspect of this work is the conversion of triclosan to DCDD directly on the polydimethylsiloxane coating of the SPME fiber. Moreover, this conversion is also confirmed in non-buffered aqueous photodegradation experiments using SPME as the extraction technique. In all the experiments of this study, analysis was carried out by gas chromatography–electronic impact mass spectrometry (GC–EI/MS).

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

Combination of gravitational SPLITT fractionation and field-flow fractionation for size-sorting and characterization of sea sediment by Myeong Hee Moon; Sung Gwon Yang; Jae Young Lee; Seungho Lee (pp. 1299-1304).

A combination of gravitational split-flow thin (SPLITT) fractionation and sedimentation/steric field-flow fractionation (Sd/StFFF) has been used for continuous size-sorting of a sediment sample and for size analysis of the collected fractions. An IAEA (International Atomic Energy Agency) sediment material was separated into four size fractions (with theoretical size ranges <1.0, 1.0–3.0, 3.0–5.0, and >5.0 μm in diameter) by means of a three-step gravitational SPLITT fractionation (GSF) for which the same GSF channel was used throughout. The GSF fractions were collected and examined by optical microscopy (OM) and by Sd/St FFF. The mean diameters of the GSF fractions measured by OM were within the size interval predicted by GSF theory, despite the theory assuming that all particles are spherical, which is not true for the sediment particles. The Sd/St FFF results showed that retention shifted toward shorter elution time (or larger size) than expected, probably because of the shape effect. The results from GSF, OM, and Sd/StFFF are discussed in detail.

Keywords: SPLITT; Gravitational SPLITT fractionation; Field-flow fractionation; Sedimentation/steric FFF; Sea sediment; Size characterization; Particle sorting

Micro-pumping flow system for spectrophotometric determination of anionic surfactants in water by André F. Lavorante; Ángel Morales-Rubio; Miguel de la Guardia; Boaventura F. Reis (pp. 1305-1309).

A novel procedure has been developed for spectrophotometric determination of anionic surfactants in water using a solenoid micro-pump as fluid-propulsion device. The proposed method is based on substitution of methyl orange (MO) by anionic surfactants in the formation of an ion-pair with the cetyl pyridine ion (CPC⁺) at pH 5.0. The flow network comprised four solenoid micro-pumps which, under microcomputer control, enabled sample and reagent introduction, and homogenisation in the reaction zone. The system is flexible and simple to operate and control, and sensitive and precise. The analytical plot for the anionic surfactant was linear between 1.43×10⁻⁶ and 1.43×10⁻⁵ mol L⁻¹ (0.5 to 5.0 mg L⁻¹; R=0.997, n=5). The relative standard deviation was 0.8% (n=11) for a sample containing 5.74×10⁻⁶ mol L⁻¹ (2 mg L⁻¹) surfactant. The limit of detection was 9.76×10⁻⁸ mol L⁻¹ (0.034 mg L⁻¹) and the sampling throughput was 60 determinations per hour. The results obtained for washing-water samples were comparable with those obtained by use of the reference method, and no significant differences at the 95% confidence level were observed.

Keywords: Micro-pump; Surfactants determination; Methyl orange; Minimisation

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Analytical and Bioanalytical Chemistry (v.381, #6)

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Analytical and Bioanalytical Chemistry (v.381, #6)