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Analytica Chimica Acta (v.614, #2)

Editorial Board (pp. i).

Contents (pp. iii-iv).

Speciation of inorganic platinum–chloride complexes in spiked environmental samples by SPE and ICP–AES by Valentina Ljubomirova; Rumyana Djingova (pp. 119-126).

A method for the separation of tetrachloroplatinate PtCl₄²⁻, and hexachloroplatinate PtCl₆²⁻, by solid-phase extraction, using a Dowex 1×10 anion exchange resin is proposed. The sequential elution and separation of PtCl₄²⁻, and PtCl₆²⁻ is achieved using selective complexing agents. The eluates, containing Pt(II) and Pt(IV) were analyzed by inductively coupled plasma–atomic emission spectroscopy (ICP–AES). Recoveries of 102% for PtCl₄²⁻ and 94% for PtCl₆²⁻ and detection limit of 15ngg⁻¹ were achieved. Using this method determination of Pt(II) and Pt(IV) in soil samples, spiked with different platinum species was performed. The comparison with GFAAS determination showed a very good agreement.

Keywords: Speciation; Tetrachloroplatinate; Hexachloroplatinate; Anoin-exchange; ICP–AES; GFAAS

Improved identification of metabolites in complex mixtures using HSQC NMR spectroscopy by Yuanxin Xi; Jeffrey S. de Ropp; Mark R. Viant; David L. Woodruff; Ping Yu (pp. 127-133).

The automated and robust identification of metabolites in a complex biological sample remains one of the greatest challenges in metabolomics. In our experiments, HSQC carbon–proton correlation NMR data with a model that takes intensity information into account improves upon the identification of metabolites that was achieved using COSY proton–proton correlation NMR data with the binary model of [Y. Xi, J.S. de Ropp, M.R. Viant, D.L. Woodruff, P. Yu, Metabolomics, 2 (2006) 221–233]. In addition, using intensity information results in easier-to-interpret “grey areas” for cases where it is not clear if the compound might be present. We report on highly successful experiments that identify compounds in chemically defined mixtures as well as in biological samples, and compare our two-dimensional HSQC analyses against quantification of metabolites in the corresponding one-dimensional proton NMR spectra. We show that our approach successfully employs a fully automated algorithm for identifying the presence or absence of predefined compounds (held within a library) in biological HSQC spectra, and in addition calculates upper bounds on the compound intensities.

Keywords: Metabolomics; Metabolite identification; Quantitative; Two-dimensional; Heteronuclear single quantum coherence; Nuclear magnetic resonance

Modelling aroma of three Italian red wines by headspace-mass spectrometry and potential functions by Carla Armanino; Maria Chiara Casolino; Monica Casale; Michele Forina (pp. 134-142).

The aromas of 41 samples of wine from two Italian regions, Piedmont and Tuscany, were analysed by headspace-mass spectrometry. Samples were from three Italian wines (Barbera, Dolcetto and Chianti) produced in the same vintage, from different grape varieties and producing zones. The headspace generating conditions were optimised by full factorial experimental design then chemometric techniques were applied to verify the discriminating power of headspace-mass spectrometry among the three wine aromas. The modelling method based on potential function, applied on the first nine significant components of the 201 measured m/ z, revealed best discrimination among the three wine aromas: cross-validated mean prediction rate of 96.7% and mean prediction rate of 83.3% on external test sets were obtained.

Keywords: Headspace-mass spectrometry; Wine aroma; Experimental design; Potential functions; Chemometrics

Use of a modified, high-sensitivity, anodic stripping voltammetry method for determination of zinc speciation in the North Atlantic Ocean by Rachel Wisniewski Jakuba; James W. Moffett; Mak A. Saito (pp. 143-152).

Zinc speciation is considered to be an important determinant of the biological availability of zinc. Yet in oceanic surface waters, characterization of zinc speciation is difficult due to the low concentrations of this essential micronutrient. In this study, an anodic stripping voltammetry method previously developed for the total determination of cadmium and lead was successfully adapted to the measurement of zinc speciation. The method differs from previous zinc speciation anodic stripping voltammetry methods in that a fresh mercury film is plated with each sample aliquot. The fresh film anodic stripping voltammetry method was compared to competitive ligand exchange cathodic stripping voltammetry in a profile from the North Atlantic Ocean. Results using the fresh film anodic stripping voltammetry method were similar to those determined using the cathodic stripping voltammetry method, though ligand concentrations determined by fresh film anodic stripping voltammetry were generally slightly higher than those determined by cathodic stripping voltammetry. There did not seem to be a systematic difference between methods for the estimates of conditional stability constants. The ligand concentration in the North Atlantic profile ranged from 0.9 to 1.5nmolL⁻¹ as determined by fresh film anodic stripping voltammetry and 0.6 to 1.3nmolL⁻¹ as determined by cathodic stripping voltammetry. The conditional stability constants determined by fresh film anodic stripping voltammetry were 10^9.8–10^10.5 and by cathodic stripping voltammetry were 10^9.8–10^11.3.

Keywords: Zinc speciation; Stripping voltammetry; North Atlantic Ocean

Copper speciation by competing ligand exchange method using differential pulse anodic stripping voltammetry with ethylenediaminetetraacetic acid (EDTA) as competing ligand by Rong Wang; Chuni L. Chakrabarti (pp. 153-160).

A technique has been developed to study chemical speciation of copper in freshwaters by competing ligand exchange (CLE) method using anodic stripping voltammetry (ASV) in the differential pulse (DP) mode with ethylenediaminetetraacetic acid (EDTA) as a competing ligand. The voltammetric behavior of Cu(II)–EDTA complex has been investigated using DPASV. When DPASV is used at an appropriate deposition potential, the inert Cu(II)–EDTA complex becomes electroactive, and is reduced directly. Furthermore, at the same deposition potential, Cu(II)–fuvic acid and Cu(II)–humic acid complexes do not contribute significantly to the analytical signal, which makes EDTA a suitable competing ligand in the determination of copper speciation using CLE–ASV. This method has been applied to freshwater samples from Rideau Canal (Ottawa, ON, Canada). The analysis of the copper titration data of these freshwater samples has indicated the presence of a very strong copper-binding ligand with a conditional stability constant of approximately 10²⁰ and a corresponding very high concentration (above 100nM) of the ligand.

Keywords: Copper speciation; Competing ligand exchange; Differential pulse anodic stripping voltammetry; Ethylenediaminetetraacetic acid (EDTA)

Application of electrospray ionization tandem mass spectrometry for the rapid and sensitive determination of cobalt in urine by Kayoko Minakata; Masako Suzuki; Osamu Suzuki (pp. 161-164).

Recently, cobalt (Co) is reported to be taken as a supplement by athletes for improving anaerobic performance. For the diagnosis of abuse, the limit of detection (LOD) of Co in the analysis should be lower than the concentrations of Co in plasma and urine of normal persons. A simple, rapid and sensitive method has been developed for the determination of Co in urine. Co was complexed with diethyldithiocarbamate (DDC) and extracted with isoamyl alcohol in the presence of citric acid. The detection of Co was achieved by injecting a 1-μL aliquot of isoamyl alcohol containing Co–DDC complex directly into an electrospray ionization tandem mass spectrometric (ESI-MS–MS) instrument without chromatographic separation. The quantification was performed using selected reaction monitoring at m/ z 291 of the product ion Co(C₄H₁₀NCS)₂⁺ which was produced by collision-induced dissociation from the precursor ion Co(DDC)₂⁺ at m/ z 355. ESI-MS–MS data were obtained in less than 10min with an LOD of 0.05μgL⁻¹ and a linear calibration range of 0.1–100μgL⁻¹ using 10μL of urine. The procedure was validated with certified reference materials (SRM 2670a and SRM 1643e). This method is suitable for the analysis of Co in the laboratories already equipped with an ESI-MS–MS instrument.

Keywords: Cobalt; Tandem mass spectrometry; Electrospray ionization; Diethyldithiocarbamate; Urine

Online stable carbon isotope ratio measurement in formic acid, acetic acid, methanol and ethanol in water by high performance liquid chromatography–isotope ratio mass spectrometry by Keiko Tagami; Shigeo Uchida (pp. 165-172).

A suitable analysis condition was determined for high performance liquid chromatography–isotope ratio mass spectrometry (HPLC–IRMS) while making sequential measurements of stable carbon isotope ratios of δ¹³C in formic acid, acetic acid, methanol and ethanol dissolved in water. For this online column separation method, organic reagents are not applicable due to carbon contamination; thus, water and KH₂PO₄ at low concentrations were tested as mobile phase in combination with a HyPURITY AQUASTAR™ column. Formic acid, acetic acid, methanol and ethanol were separated when 2mM KH₂PO₄ aqueous solution was used. Under the determined analysis condition for HPLC–IRMS, carbon concentrations could be measured quantitatively as well as carbon isotope ratio when carbon concentration was higher than 0.4mML for each chemical.

Keywords: Formic acid; Acetic acid; Methanol; Ethanol; HPLC–IRMS; Stable carbon isotope ratio

Studies on the mechanism of the peroxyoxalate chemiluminescence reaction by Sarah A. Tonkin; Richard Bos; Gail A. Dyson; Kieran F. Lim; Richard A. Russell; Simon P. Watson; Christopher M. Hindson; Neil W. Barnett (pp. 173-181).

Further consideration has been given to the reaction pathway of a model peroxyoxalate chemiluminescence system. Again utilising doubly labelled oxalyl chloride and anhydrous hydrogen peroxide, 2D EXSY¹³C nuclear magnetic resonance (NMR) spectroscopy experiments allowed for the characterisation of unknown products and key intermediate species on the dark side of the peroxyoxalate chemiluminescence reaction. Exchange spectroscopy afforded elucidation of a scheme comprised of two distinct mechanistic pathways, one of which contributes to chemiluminescence.¹³C NMR experiments carried out at varied reagent molar ratios demonstrated that excess amounts of hydrogen peroxide favoured formation of 1,2-dioxetanedione: the intermediate that, upon thermolysis, has been long thought to interact with a fluorophore to produce light.

Keywords: Peroxyoxalate chemiluminescence; Mechanism; Key intermediates; 2D EXSY; ¹³; C nuclear magnetic resonance spectroscopy

Label-free cell-based assay using localized surface plasmon resonance biosensor by Tatsuro Endo; Shohei Yamamura; Kagan Kerman; Eiichi Tamiya (pp. 182-189).

For an understanding of the life activities, the analysis of cells, which are the smallest units of life form, has a significant impact on biology and biotechnology. In this study, we propose a novel label-free cell-based assay that is based on localized surface plasmon resonance (LSPR) biosensor, which is excited using core–shell structured nanoparticle layer substrate. To demonstrate the promising properties of our LSPR-based label-free cell-based assay, we performed the detection of the cell metabolites using the isolated cells from mouse thymus. For detection of the cellular metabolites, the refractive index change by the specific interaction between the antigen and antibody was detected on the antibody immobilized LSPR-based biosensor. Using our LSPR-based biosensor, the optical characteristics were monitored for the detection of specific reactions between antibody and cell metabolites. As a result, the detection limit of this antibody immobilized LSPR-based biosensor was 10pgmL⁻¹. Furthermore, the time-course analysis of cell metabolisms using the isolated cells from mouse thymus was also achieved. From these results, the LSPR-based biosensor provides a promising platform with attractive advantages for the detection of biomolecular interactions at low-cost in a simplified experimental set-up with a low sample volume.

Keywords: Localized surface plasmon resonance (LSPR); Biosensor; Cell-based assay; Nanoparticles

Determination of aliphatic amines by high-performance liquid chromatography-amperometric detection after derivatization with naphthalene-2,3-dicarboxaldehyde by Sushma Lamba; Arti Pandit; Sunil Kumar Sanghi; V. Sorna Gowri; Ankita Tiwari; Vishal Kumar Baderia; Deepesh Kumar Singh; Preeti Nigam (pp. 190-195).

A simple and sensitive liquid chromatographic method has been developed for the determination of low molecular weight aliphatic amines after their pre-column derivatization with naphthalene-2,3-dicarboxaldehyde (NDA). Derivatization conditions, including the NDA concentration, reaction pH and reaction time have been investigated for method optimization. The chromatographic separation of five amines was performed on ABZ PLUS column using mobile phase of methanol–water (80:20, v/v) at a flow rate of 0.2mLmin⁻¹. The detection was carried out with a 6mm glassy carbon electrode at the applied potential of 0.7V versus Ag/AgCl reference electrode. The detection limits were between 23.3 and 34.4nmolL⁻¹ of amines with a sample injection volume of 2μL. The present method was applied for the determination of aliphatic amines in lake water. The recovery ranged 52.2–127.9%. The RSD in analytes retention time was less than 0.3% and 2.4% for intra- and inter-day analyses, respectively. The RSD in peak area was below 5.8% for both intra-day and inter-day analyses. The total analysis was completed within 20min.

Keywords: Aliphatic amines; High-performance liquid chromatography; Amperometric detection; Naphthalene-2,3-dicarboxaldehyde; Derivatization

Quantitative analysis of flavonoids and phenolic acids in Arnica montana L. by micellar electrokinetic capillary chromatography by Markus Ganzera; Christoph Egger; Christian Zidorn; Hermann Stuppner (pp. 196-200).

Arnica montana preparations have been used in Europe for centuries to treat skin disorders. Among the biologically active ingredients in the flower heads of the plant are sequiterpenes, flavonoids and phenolic acids. For the simultaneous determination of compounds belonging to the latter two groups a micellar electrokinetic capillary chromatography (MEKC) method was developed and validated. By using an electrolyte solution containing 50mM borax, 25mM sodium dodecyl sulfate and 30% of acetonitrile the separation of seven flavonoids and four caffeic acid derivatives was feasible in less than 20min. The optimized system was validated for repeatability ( σ_rel≤4.4%), precision (inter-day σ_rel≤8.13%, intra-day σ_rel≤4.32%), accuracy (recovery rates from 96.8 to 102.4%), sensitivity (limit of detection (LOD)≤4.5μgmL⁻¹) and linearity ( R²≥0.9996), and then successfully applied to assay several plant samples. In all of them the most dominant flavonoid was found to be quercetin 3- O-glucuronic acid, whereas 3,5-dicaffeoylquinic acid was the major phenolic acid; the total content of flavonoids and phenolic acids varied in the samples from 0.60 to 1.70%, and 1.03 to 2.24%, respectively.

Keywords: Arnica montana; Micellar electrokinetic capillary chromatography; Flavonoids; Phenolic acids; Validation

Determination of fluoxetine in plasma by gas chromatography–mass spectrometry using stir bar sorptive extraction by Christian Fernandes; Els Van Hoeck; Pat Sandra; Fernando M. Lanças (pp. 201-207).

This article presents a method employing stir bar sorptive extraction (SBSE) with in situ derivatization, in combination with either thermal or liquid desorption on-line coupled to gas chromatography–mass spectrometry for the analysis of fluoxetine in plasma samples. Ethyl chloroformate was employed as derivatizing agent producing symmetrical peaks. Parameters such as solvent polarity, time for analyte desorption, and extraction time, were evaluated. During the validation process, the developed method presented specificity, linearity ( R²>0.99), precision (R.S.D.<15%), and limits of quantification (LOQ) of 30 and 1.37pgmL⁻¹, when liquid and thermal desorption were employed, respectively. This simple and highly sensitive method showed to be adequate for the measurement of fluoxetine in typical and trace concentration levels.

Keywords: Stir bar sorptive extraction; Fluoxetine; Thermal desorption; In situ derivatization; Plasma

Molecular beacons: A real-time polymerase chain reaction assay for detecting Escherichia coli from fresh produce and water by S. Sandhya; Wilfred Chen; Ashok Mulchandani (pp. 208-212).

Molecular beacons (MBs) are oligonucleotide probes that fluoresce upon hybridization. The development of a real-time polymerase chain reaction (PCR) assay to detect the presence of Escherichia coli using these fluorogenic reporter molecules is reported. MBs were designed to recognize a 19-bp region of the uid A gene, coding for an enzyme β-glucuronidase. The specificity of the MB-based PCR assay was evaluated for various E. coli strains as well as bacteria species that are present in nature. The capability of the assay to detect E. coli in drinking water and produce was demonstrated. Positive detection of E. coli was demonstrated when >10¹CFUmL⁻¹ (colony forming unit) was present in the water samples and fresh produce after 18h of enrichment. These assays could be carried out entirely in sealed PCR tubes, enabling rapid and semiautomated detection of E. coli in food and environmental samples.

Keywords: Escherichia coli; Real-time polymerase chain reaction; Rapid microbial detection; Food; Water

Amperometric sensors based on poly(3,4-ethylenedioxythiophene)-modified electrodes: Discrimination of white wines by L. Pigani; G. Foca; K. Ionescu; V. Martina; A. Ulrici; F. Terzi; M. Vignali; C. Zanardi; R. Seeber (pp. 213-222).

The voltammetric responses on selected white wines of different vintages and origins have been systematically collected by three different modified electrodes, in order to check their effectiveness in performing blind analysis of similar matrices. The electrode modifiers consist of a conducting polymer, namely poly(3,4-ethylenedioxythiophene) (PEDOT) and of composite materials of Au and Pt nanoparticles embedded in a PEDOT layer. Wine samples have been tested, without any prior treatments, with differential pulse voltammetry technique. The subsequent chemometric analysis has been carried out both separately on the signals of each sensor, and on the signals of two or even three sensors as a unique set of data, in order to check the possible complementarity of the information brought by the different electrodes. After a preliminary inspection by principal component analysis, classification models have been built and validated by partial least squares-discriminant analysis. The discriminant capability has been evaluated in terms of sensitivity and specificity of classification; in all cases quite good results have been obtained.

Keywords: Amperometric sensor; Electronic tongue; Conducting polymer; White wines; Principal component analysis; Partial least squares-discriminant analysis

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Analytica Chimica Acta (v.614, #2)