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Analytica Chimica Acta (v.597, #1)

Contents (pp. v-vi).

Editorial Board (pp. co1).

Dynamic liquid-phase microextraction of three phthalate esters from water samples and determination by gas chromatography by Jing Xu; Pei Liang; Taozhi Zhang (pp. 1-5).

A fast and simple method, which involves dynamic liquid-phase microextraction followed by gas chromatography with flame ionization detection, has been developed to facilitate the identification and quantification of three phthalate esters (dimethyl phthalate (DMP), diethyl phthalate (DEP), and di- n-butyl phthalate (DnBP)) in water samples. Experimental parameters affecting the extraction efficiency, such as extraction solvent, solvent volume, dwell time and extraction frequency were investigated. Under the optimal conditions, the method yields a linear calibration curve over three orders of magnitude for the target analytes. The limits of detection of DMP, DEP and DnBP were 4.30, 0.66 and 0.43ngmL⁻¹, respectively, and relative standard deviations at the 100ngmL⁻¹ level were 6.4%, 5.4% and 5.2%, respectively ( n=6). Lake water, tap water and bottled mineral water samples were successfully analyzed using the proposed method.

Keywords: Dynamic liquid-phase microextraction; Gas chromatography; Phthalate esters; Water analysis

Synthesis and application of a carbamazepine-imprinted polymer for solid-phase extraction from urine and wastewater by A. Beltran; E. Caro; R.M. Marcé; P.A.G. Cormack; D.C. Sherrington; F. Borrull (pp. 6-11).

A molecularly imprinted polymer (MIP) designed to enable the selective extraction of carbamazepine (CBZ) from effluent wastewater and urine samples has been synthesised using a non-covalent molecular imprinting approach. The MIP was evaluated chromatographically in the first instance and its affinity for CBZ also confirmed by solid-phase extraction (SPE). The optimal conditions for SPE consisted of conditioning of the cartridge using acidified water purified from a Milli-Q system, loading of the sample under basic aqueous conditions, clean-up using acetonitrile and elution with methanol. The attractive molecular recognition properties of the MIP gave rise to good CBZ recoveries (80%) when 100mL of effluent water spiked with 1μgL⁻¹ was percolated through the polymer. For urine samples, 2mL samples spiked with 2.5μgL⁻¹ CBZ were extracted with a recovery of 65%. For urine, the linear range was 0.05–24mgL⁻¹, the limit of detection was 25μgL⁻¹ and precision, expressed as relative standard deviation at 0.5mgL⁻¹ ( n=3), was 3.1% and 12.6% for repeatability and reproducibility between days, respectively.

Keywords: Molecularly imprinted polymer; Carbamazepine; Solid-phase extraction; Urine samples; Wastewater

A new ion-imprinted silica gel sorbent for on-line selective solid-phase extraction of dysprosium(III) with detection by inductively coupled plasma-atomic emission spectrometry by Nan Zhang; Bin Hu; Chaozhang Huang (pp. 12-18).

Dysprosium(III)-imprinted thenoyltrifluoroacetone (TTA) modified silica gel sorbent was synthesized by surface imprinting technique and was employed as a selective solid-phase extraction material for flow injection solid-phase extraction on-line coupled with inductively coupled plasma-atomic emission spectrometry (ICP-AES) determination of Dy(III). The largest selectivity coefficient for Dy(III) in the presence of competitive ions such as La(III), Nd(III) and Gd(III) was above 350. The static adsorption capacity and selectivity coefficient of the imprinted sorbent are higher than those of the non-imprinted sorbent and the imprinted TTA modified silica gel sorbent offered a fast kinetics for the adsorption and desorption of Dy(III). With a sample loading flow rate of 2.5mLmin⁻¹ for 48s preconcentration and elution flow rate of 1.5mLmin⁻¹ for 8s elution, an enrichment factor of 10 and the sample frequency of 40sampleh⁻¹ were obtained. Detection limits (3 σ) based on three times standard deviations of the blanks by eight replicates was 0.2ngmL⁻¹ and the precisions (R.S.D.s) was 1.5% ( n=8, c=40ngmL⁻¹). To validate the proposed method, two certified reference materials of GBW07401 soil and GBW07301a sediment were analyzed and the determined values were in a good agreement with the certified values. The method is rapid, selective, sensitive and applicable to the determination of trace Dy(III) in environmental samples with complicated matrix.

Keywords: Dysprosium(III); Ion-imprinted silica gel sorbent; Surface imprinting technique; On-line solid-phase extraction; Inductively coupled plasma-atomic emission spectrometry

Rapid determination of Papaver somniferum alkaloids in process streams using monolithic column high-performance liquid chromatography with chemiluminescence detection by Jason W. Costin; Simon W. Lewis; Stuart D. Purcell; Lucy R. Waddell; Paul S. Francis; Neil W. Barnett (pp. 19-23).

We have combined high-performance liquid chromatography (HPLC) separations using a monolithic column with acidic potassium permanganate and tris(2,2′-bipyridyl)ruthenium(II) chemiluminescence detection in a rapid and highly sensitive method to monitor the process of extracting opiate alkaloids from Papaver somniferum. Due to the high flow rates allowed with the monolithic column and the inherent selectivity of the chemiluminescence reactions, the four predominant alkaloids – morphine, codeine, oripavine and thebaine – were determined in less than 2min. The results obtained with numerous process samples compared favourable with those of the standard HPLC methodology. Limits of detection were 1×10⁻¹⁰M, 5×10⁻¹⁰M, 5×10⁻¹⁰M and 1×10⁻⁹M, for morphine, codeine, oripavine and thebaine, respectively.

Keywords: Monolithic column; Alkaloids; Chemiluminescence

Identification of major metal complexing compounds in Blepharis aspera by Edward Eddie Mmatli; Helle Malerød; Steven Ray Wilson; Berhanu Abegaz; Tyge Greibrokk; Elsa Lundanes; Karl E. Malterud; Dirk Petersen; Frode Rise (pp. 24-31).

Verbascoside and isoverbascoside, present at 0.7% and 0.2% (w/w dryweight), were identified to be major compounds that could contribute to the metal complexation in Blepharis aspera collected in Botswana, Africa. The metallophyte B. aspera has high ability to cope with a high level of metal accumulation. The presence of metal complexing compounds and/or antioxidants can prevent oxidative reactions in lipids, proteins and DNA that take place due to the metal accumulation. On-line liquid chromatography–solid phase extraction–nuclear magnetic resonance (LC–SPE–NMR) was applied for the identification, while electrospray-mass spectrometry (ESI-MS) and UV-vis spectroscopy was used to assess whether these compounds can complex with metals. It was found that verbascoside and isoverbascoside may form complexes with nickel, iron (verbascoside only) and copper. Thus, the presence of verbascoside and isoverbascoside can explain the survival of B. aspera in mineral-rich areas.

Keywords: Blepharis aspera; Botswana; Liquid chromatography–nuclear magnetic resonance; Verbascoside; Isoverbascoside

In-drop derivatisation liquid-phase microextraction assisted by ion-pairing transfer for the gas chromatographic determination of phenolic endocrine disruptors by Yiannis C. Fiamegos; Constantine D. Stalikas (pp. 32-40).

A novel in-drop derivatisation liquid-phase microextraction procedure with an ion-pairing agent is developed and optimised for the extraction of endocrine-disrupting chemicals. The ethyl esters of the analytes were rapidly formed in the organic drop and analysed by gas chromatography. The effects of various parameters such as rate and time of agitation, ion-pairing agent and reactant concentration, pH and temperature were studied systematically to optimise the process and bring out the locale of reaction in the organic drop. A study of the mechanistic pathways of the overall procedure is attempted leading to interesting findings and delineating important points of the kinetics and mechanism. A mechanistic model is proposed on the basis of the theory of mass transfer with chemical reaction in two liquid phases. The O-ethoxycarbonyl derivatisation appears to take place in the bulk organic phase. The system provides insight into the first reported analytical case of single-drop extraction–preconcentration–derivatisation assisted by an ion-pairing transfer and has all of the interesting facets of chemical reaction in which the role of mass transfer comes into picture.The analytical features of the method are acceptable and the overall relative standard deviations of the intra-day repeatability ( n=5) and inter-day reproducibility were <3.9% and <5.4%, respectively, for gas chromatography–mass spectrometry analyses and <4.3% and <7.1% for gas chromatography–flame ionisation detection analyses. The method was applicable to urine and surface water samples. The LODs ranged between 0.2–1.3ngmL⁻¹ and 8.5–26.5ngmL⁻¹ for GC/MS and GC/FID analyses, respectively.

Keywords: Single-drop liquid-phase microextraction; Ion-pairing transfer; Ethyl chloroformate derivatisation; Endocrine disruptors

Off-line coupling of preparative capillary zone electrophoresis with microwave-assisted acid hydrolysis and matrix-assisted laser desorption ionization mass spectrometry for protein sequencing by Mahmoud M. Yassine; Nan Guo; Hongying Zhong; Liang Li; Charles A. Lucy (pp. 41-49).

An off-line coupling of capillary electrophoresis (CE) with microwave-assisted acid hydrolysis/matrix-assisted laser desorption ionization mass spectrometry (MAAH/MALDI) has been developed for protein identification and characterization. Preparative scale protein separations enable collection of 10–50pmol of purified cytochrome c for subsequent sequencing using MAAH/MALDI. To reduce protein adsorption onto the silica surface, the cationic surfactant-based coatings, dimethylditetradecylammonium bromide and dimethyldioctadecylammonium bromide, are employed. The choice of the buffer conditions is critical for both the preparative CE and MAAH/MALDI method. The use of high buffer concentrations (100mM Bis–tris) reduces electromigration dispersion, but suppressed MALDI ionization such that a peptide sequence coverage of only 80% was achieved at a sample loading of 40gL⁻¹ of each cytochrome c. By reducing the buffer concentration to 25mM Bis–tris, the sequence coverage increased to 95% at a sample loading of 40gL⁻¹.

Keywords: Capillary electrophoresis; Microwave; Protein digestion; Preparative separation; Proteomics; Matrix-assisted laser desorption ionization time-of-flight mass spectrometry

Screen-printed electrodes as impedimetric immunosensors for the detection of anti-transglutaminase antibodies in human sera by T. Balkenhohl; F. Lisdat (pp. 50-57).

The concentration of anti-transglutaminase antibodies in human sera is an important analytical marker for the diagnosis of the autoimmune disorder celiac disease. In this work, an immunosensor for the electrochemical detection of anti-transglutaminase antibodies in human sera was developed. The immunosensor is based on the immobilization of transglutaminase onto screen-printed gold electrodes which were covered with a polyelectrolyte layer of poly (sodium-4-styrensulfonic acid). The antigen–antibody interaction was evaluated using an amplification step: incubation with peroxidase (POD)-labeled immunoglobulins and subsequent biocatalytic oxidation of 3-amino-9-ethylcarbazole (AEC). Changes in the interfacial properties of the sensor electrode were determined by electrochemical impedance spectroscopy (EIS). Impedance spectra could be fitted to a Randles equivalent circuit containing a constant phase element (CPE). Furthermore, it was shown that impedance measurements could be simplified by performing EIS at only two selected frequencies, without loss of reliability. Incubation of these disposable immunosensor chips with various anti-transglutaminase antibody concentrations resulted in changes in their charge transfer resistance ( R_ct). Thereby, a calibration graph could be established. Finally, immunosensors were used for characterizing different human sera with respect to their anti-transglutaminase autoantibody concentration of the IgG and IgA type.

Keywords: Immunosensor; Electrochemical impedance spectroscopy; Transglutaminase; Anti-transglutaminase antibodies; Poly (sodium-4-styrensulfonic acid); Screen-printed electrodes

Study of fibrinogen adsorption on hydroxyapatite and TiO₂ surfaces by electrochemical piezoelectric quartz crystal impedance and FTIR–ATR spectroscopy by Qin Yang; Youyu Zhang; Meiling Liu; Min Ye; YuQin Zhang; Shouzhuo Yao (pp. 58-66).

The electrochemical piezoelectric quartz crystal impedance (EQCI), a combined technique of piezoelectric quartz crystal impedance (PQCI), electrochemical impedance (EI), and Fourier transform infrared spectroscopy–attenuated total internal reflectance spectroscopy (FTIR–ATR) were used to in situ study the adsorption process of fibrinogen onto the surface of biomaterials—TiO₂ and hydroxyapatite (Ca₅(PO₄)₃OH, HAP). The equivalent circuit parameters, the resonance frequencies and the half peak width of the conductance spectrum of the two biomaterial-modified piezoelectric quartz crystal (PQC) resonances as well as the FTIR–ATR spectra of fibrinogen during fibrinogen adsorption on TiO₂ and HAP particles modified electrode surface were obtained. The adsorption kinetics and mechanism of fibrinogen were investigated and discussed as well. The results suggested that two consecutive steps occurred during the adsorption of fibrinogen onto TiO₂ and hydroxyapatite (HAP) surface. The fibrinogen molecules were firstly adsorbed onto the surface, and then the rearrangement of adsorbed fibrinogen or multi-layered adsorption occurred. The FTIR–ATR spectroscopy investigations showed that the secondary structure of fibrinogen molecules was altered during the adsorption and the adsorption kinetics of fibrinogen related with the variety of biomaterials. These experimental results suggest a way for enriching biological analytical science and developing new applications of analytical techniques, such as PQCI, EI, and FTIR–ATR.

Keywords: Electrochemical quartz crystal impedance; Fourier transform infrared spectroscopy–attenuated total internal reflectance spectroscopy; Adsorption kinetics; TiO; ₂; Hydroxyapatite; Fibrinogen

The different behaviors of three oxidative mediators in probing the redox activities of the yeast Saccharomyces cerevisiae by Jinsheng Zhao; Min Wang; Zhenyu Yang; Zhong Wang; Huaisheng Wang; Zhengyu Yang (pp. 67-74).

The different behaviors of three lipophilic mediators including 2-methyl-1,4-naphthalenedione(menadione), 2,6-dichlorophenolindophenol (DCPIP) and N, N, N′, N′-tetramethyl- p-phenylenediamine (TMPD) in probing the redox activity of the yeast Saccharomyces cerevisiae were studied by several comparative factor-influencing experiments. Hydrophilic ferricyanide was employed as an extracellular electron acceptor, and constituted dual mediator system with each of three lipophilic mediators. Limiting-current microelectrode voltammetry was used to measure the quantity of ferrocyanide accumulations, giving a direct measure of the redox activity. It was found that under anaerobic condition, menadione interacts with anaerobic respiration pathway, whereas DCPIP and TMPD interact with fermentation pathway in the yeast. Based on the understanding of the interaction between the yeast and each of three mediators, three mediators were respectively employed in evaluating the toxicity of acetic acid on S. cerevisiae and, the results for the first showed that the mediators are complementary to each other when used as electron carriers in biotoxicity assay.

Keywords: Electrochemical; Mediators; Redox activity; S. cerevisiae

Assessment of the uncertainty budget for the amperometric measurement of dissolved oxygen by Paola Fisicaro; Annemie Adriaens; Enzo Ferrara; Enrico Prenesti (pp. 75-81).

This work aimed at identifying the main sources of uncertainty for the measurement of dissolved oxygen concentration in aqueous solutions. The experimental apparatus consists of an amperometric cell based on the Clark-type sensor. The corresponding uncertainty budget was assessed, this being a fundamental step for the validation of a measurement method. The principle of the measurement, as well as the procedure for the set-up and the characterisation of the cell, are described. The measurement equation was defined as a combination of Faraday's and Fick's laws, and a method was worked out for the empirical determination of the diffusivity parameter. In this connection, the solutions of oxygen were standardised by way of the Winkler's titration, as suggested by the ISO Guide 5813 and 5814. With this approach we aimed at contributing to the development of a potential primary method of measurement. A discussion of all the contributions to the overall uncertainty is reported, allowing operators to locate the largest ones and plan specific improvements.

Keywords: Clark-type sensors; Amperometric measurement; Dissolved oxygen measurement uncertainty; Validation

Fullerene-C₆₀-modified electrode as a sensitive voltammetric sensor for detection of nandrolone—An anabolic steroid used in doping by Rajendra N. Goyal; Vinod K. Gupta; Neeta Bachheti (pp. 82-89).

The electrochemical behaviour of nandrolone is investigated by cyclic, differential pulse and square-wave voltammetry in phosphate buffer system at fullerene-C₆₀-modified electrode. The modified electrode shows an excellent electrocatalytic activity towards the oxidation of nandrolone resulting in a marked lowering in the peak potential and considerable improvement of the peak current as compared to the electrochemical activity at the bare glassy carbon electrode. The oxidation process is shown to be irreversible and diffusion-controlled. A linear range of 50μM to 0.1nM is obtained along with a detection limit and sensitivity of 0.42nM and 0.358nAnM⁻¹, respectively, in square-wave voltammetric technique. A diffusion coefficient of 4.13×10⁻⁸cm²s⁻¹ was found for nandrolone using chronoamperometry. The effect of interferents, stability and reproducibility of the proposed method were also studied. The described method was successfully employed for the determination of nandrolone in human serum and urine samples. A cross-validation of observed results by GC–MS indicates that the results are in good agreement with each other.

Keywords: Fullerene-C; ₆₀; -modified electrode; Nandrolone; Electrocatalysis; Square-wave voltammetry; Biological fluids

Cucurbit[ n]urils-induced room temperature phosphorescence of quinoline derivatives by Lan Mu; Xiao-Bing Yang; Sai-Feng Xue; Qian-Jiang Zhu; Zhu Tao; Xi Zeng (pp. 90-96).

The cucurbit[7,8]urils (Q[7] and Q[8])-induced room temperature phosphorescence (RTP) of quinoline and its derivatives were firstly found in the cucurbit[ n]urils chemistry. The luminophores (quinolines) and their RTP are affected by the concentration of different Q[ n]s, heavy metal ions and amounts, and pH. The RTP lifetime of the luminophore has been investigated. In presence of Na₂SO₃, the cation Tl⁺ led to stronger Q[ n]-induced RTP, while the RTP lifetimes of luminophore/Q[7 or 8]/KI were generally longer than that of luminophore/Q[7 or 8]/TlNO₃, the RTP lifetimes of these systems were between 0.18 and 47.4ms. Contrary to the stable 1:2 Q[8]:guest ternary inclusion complexes at lower pHs, as suggested by¹H NMR, electronic absorption and fluorescence spectroscopy, low Q[8]-induced room temperature phosphorescence was observed. However, at higher pHs, high intensity of cucurbit[ n]urils-induced room temperature phosphorescence of these quinoline derivatives were observed, and a 1:1 Q[8]:guest inclusion complex was formed. Investigations of dependence of RTP intensity on concentration of Q[ n] revealed that the highest intensity of the Q[ n]-induced RTP was observed at a low mole ratio of host:guest, which is closed to 1:1. It was presumably resulted from the strong interaction of Q[ n] and these guests due to the combined hydrophobic cavity interaction and the hydrophilic portal interaction of the cucurbit[ n]urils with the nitrogen heterocycles guest.

Keywords: Room temperature phosphorescence; Cucurbit[7,8]urils; Quinoline and its derivatives; Potassium iodide; Thallium nitrate

Fluorescence detection of single-nucleotide polymorphisms with two simple and low cost methods: A double-DNA-probe method and a bulge form method by Na Li; Ling Mei; Yu Xiang; Aijun Tong; Seiichi Nishizawa; Norio Teramae (pp. 97-102).

Two 10-mer DNA probes, or one 20-mer DNA probe, respectively, hybridize with a 21-mer target DNA to form a vacancy or bulge opposite the target nucleotide. The former double-DNA-probe method and the latter bulge form method are applicable to the detection of single-nucleotide polymorphisms (SNPs). A small fluorescent dye enters into the vacancy or bulge and binds with a target nucleotide via a hydrogen bonding interaction, which causes fluorescence quenching. The interaction between fluorescent dye and the target nucleotide is confirmed by measuring the melting temperature and fluorescence spectra. The fluorescent dye, ADMND (2-amino-5,7-dimethyl-1,8-naphthyridine), is found to selectively bind with C over A or G. The methods proposed here are economic, convenient, and effective for the fluorescence detection of SNPs. Finally, the double-DNA-probe method and bulge form method are successfully applied to the detection of C/G and C/A mutations in the estrogen receptor 2 gene and progesterone receptor gene using ADMND.

Keywords: Single-nucleotide polymorphisms; Fluorescence detection; Double-DNA-probe method; Bulge form method

Direct quantitative evaluation of complex substances using computer screen photo-assisted technology: The case of red wine by Adriano Alimelli; Daniel Filippini; Roberto Paolesse; Simonetta Moretti; Gaetano Ciolfi; Arnaldo D’Amico; Ingemar Lundström; Corrado Di Natale (pp. 103-112).

The combination of computer monitors and webcams has been recently demonstrated to behave as a sort of spectrophotometer able to classify and recognize substances according to their light absorption and emission properties. This measurement technique is known as computer screen photoassisted technique (CSPT).In this paper, it is demonstrated for the first time and in the case of a complex sample such as red wine, that also quantification of integral parameters (colour indicators) and specific compounds (total anthocyanins and polyphenols) is possible through a multivariate analysis of CSPT fingerprints. Most of the properties of the method are due to the combination of light emission and absorption properties that are captured by the CSPT platform. Thanks to this combination, a CSPT fingerprint may contain a comparable amount of information with respect to standard spectrophotometers.Wine measurements were performed on intact samples without the intervention of chemical mediators. The regression models, built by Partial Least Squares, obtained errors of estimation of colour parameters, total polyphenols and anthocyanines that are comparable with those typical of the standard methods in use.Since computation functionalities, video capture and display are embedded in a steadily growing number of ubiquitously distributed equipments (from portable computers to cellular phones), these results indicate a viable methodology for low-cost and largely diffused analytical capabilities.

Keywords: Spectrophotometry; Red wine; Colour indicators; Polyphenols; Computer screen photoassisted technique

Simultaneous determination of salbutamol sulphate, bromhexine hydrochloride and etofylline in pharmaceutical formulations with the use of four rapid derivative spectrophotometric methods by H.N. Dave; R.C. Mashru; A.R. Thakkar (pp. 113-120).

Four simple, rapid, accurate, precise, reliable and economical spectrophotometric methods have been proposed for simultaneous determination of salbutamol sulphate (SS), bromhexine hydrochloride (BH) and etofylline (ET) in pure and commercial formulations without any prior separation or purification. They were first derivative zero crossing spectrophotometry (method 1), simultaneous equation method (method 2), derivative ratio spectra zero crossing method (method 3) and double divisor ratio spectra derivative method (method 4). The ranges for SS, BH and ET were found to be 1–35μgmL⁻¹, 4–40μgmL⁻¹ and 5–80μgmL⁻¹. For methods 1 and 2, the values of limit of detection (LOD) were 0.2314μgmL⁻¹, 0.4865μgmL⁻¹ and 0.2766μgmL⁻¹ and the values of limit of quantitation (LOQ) were 0.7712μgmL⁻¹, 1.6217μgmL⁻¹ and 0.9221μgmL⁻¹ for SS, BH and ET, respectively. For method 3, LOD values were 0.3297μgmL⁻¹, 0.2784μgmL⁻¹ and 0.7906μgmL⁻¹ and LOQ values were 0.9325μgmL⁻¹, 0.9282μgmL⁻¹ and 2.6352μgmL⁻¹ for SS, BH and ET, respectively. For method 4, LOD values were 0.3161μgmL⁻¹, 0.2495μgmL⁻¹ and 0.2064μgmL⁻¹ and LOQ values were 0.9869μgmL⁻¹, 0.8317μgmL⁻¹ and 0.6879μgmL⁻¹ for SS, BH and ET. The precision values were less then 2% R.S.D. for all four methods. The common excipients and additives did not interfere in their determinations. The results obtained by the proposed methods have been statistically compared by means of Student t-test and by the variance ratio F-test.

Keywords: First derivative zero crossing spectrophotometry; Simultaneous equation method; Derivative ratio spectra zero crossing spectrophotometry; Double divisor ratio spectra derivative spectrophotometry; Salbutamol sulphate; Bromhexine hydrochloride; Etofylline

Feasibility of electron impact and electron capture negative ionisation mass spectrometry for the trace determination of tri- to deca-brominated diphenyl ethers in human samples by Belén Gómara; Laura Herrero; María José González (pp. 121-128).

The applicability of two different MS ionisation modes (EI and ECNI) for the determination of PBDEs at low-trace levels in small-size (up to 1mL) human samples was compared. The instrumental precision, expressed as R.S.D., obtained for both ionisation modes was similar and lower than 6% (repeatability) and 12% (intermediate precision) for all congeners investigated, except PBDE 209. The LODs obtained when using the ECNI-MS operation mode (6–507fg) were lower than those found in EI-MS experiments (9 and 10,909fg), mainly for those congeners with a high bromination degree, i.e., hepta- to deca-BDEs. The selectivity of the ECNI-MS method proposed in the present work was improved by using two ions of the [M−H_xBr_y]⁻ cluster as both qualifier and quantifier ions. For the final validation of the methods, serum and breast milk samples from two different inter-laboratory exercises were analysed. A good agreement was found between the results obtained using the proposed methods and the results provided by the different inter-laboratory organisations, but only ECNI-MS provided the low-LODs necessary for the quantification of high brominated congeners (mainly, PBDEs 196, 197 and 209) at low concentration levels in small-size human samples. Finally, the ECNI-MS method was applied to real-life samples obtained from the Spanish population and the preliminary results obtained were in the same range as those found in other European and Asian regions and lower than the concentrations reported in USA populations.

Keywords: Polybrominated diphenyl ethers electron impact ionisation; Electron capture negative ionisation; Mass spectrometry; Human samples

A three-factor Doehlert matrix design in optimising the determination of octadecyltrimethylammonium bromide by cation-exchange chromatography with suppressed conductivity detection by Tommaso R.I. Cataldi; Donatella Orlando; Donatella Nardiello; Alessandra Rubino; Giuliana Bianco; Salvatore Abate; Rosanna Ciriello; Antonio Guerrieri (pp. 129-136).

A simple and effective chromatographic method with suppressed conductivity detection was developed and validated to determine dissolved samples of octadecyltrimethylammonium bromide (C₁₈H₃₇N⁺Me₃Br⁻, ODTAB) for purity testing. A response surface methodology generated with a Doehlert matrix design was applied to optimize the chromatographic and detection conditions in ion-exchange chromatography (IEC) with conductivity detection in the chemical suppression mode. A three-factor Doehlert design was performed to fit a second-order model and jointly optimize the peak intensity and shorten analysis time through a global desirability function. Regenerant flow rate, volume fraction of acetonitrile in the acidic eluent and its flow rate were studied at seven, five and three levels, respectively. The optimized separation and detection conditions were accomplished by using a cation-exchange column eluted at 0.5mLmin⁻¹ with an isocratic mobile phase composed of CH₃CN and 25mN H₂SO₄, 82/18 (v/v). Chemical suppression of ionic conductivity was performed by 100mN tetrabutylammonium hydroxide (TBAOH) as a regenerant at a flow-rate of 4.0mLmin⁻¹. Remarkably good agreement was found between predicted and experimental values of signal intensity and chromatographic retention. With the developed method, a linear calibration curve of ODTA⁺ as bromide salt from 5 to 1000ppm was obtained using hexadecyltrimethylammonium bromide as internal standard. The estimated limit of detection was 0.3ppm (S/N=3). The effectiveness of electrochemically suppressed conductivity detection of ODTA⁺ was also demonstrated, thus making easier the whole detection operation and instrumental needs as well.

Keywords: Experimental design; Doehlert design; Chemometrics; Surfactant; Octadecyltrimethylammonium ion; Ion chromatography; Suppressed conductivity detection

Luminescence decay time encoding of magnetic micro spheres for multiplexed analysis by Torsten Mayr; Christoph Moser; Ingo Klimant (pp. 137-144).

Magnetic microspheres are optically encoded by doping with three luminescent dyes. The combination of a fluorophore with a nanosecond decay profile and two phosphorescent Ruthenium metal ligand complexes with a microsecond decay profile generates a characteristic signature described by three features: bead brightness, luminescent decay time and dual lifetime referencing (DLR). The beads are identified by time resolved imaging in the microsecond range. A series of fluorophores is tested and the interference of the resulting luminescent code in the red and green label detection channels is investigated. A detailed staining procedure is worked out to increase the staining efficiency of the dyes with hydrophilic character into the lipophilic polystyrene microspheres. A mathematical model is established to calculate the dye amounts that are needed for staining a bead family with a specific feature set. Nineteen bead families were prepared representing the grid points in the three planes of a cube referring to the three features. The coefficient of variation over all bead families is 7%, 1.4% and 1.6% for bead brightness, luminescence decay time and DLR, respectively. The combination of these features and the bead size as additional feature enables the creation of 840 distinguishable bead families.

Keywords: Multiplex analysis; Suspension arrays; Magnetic microspheres; Optical encoded microspheres; Time resolved imaging

An enhanced biosensor for glutamate based on self-assembled carbon nanotubes and dendrimer-encapsulated platinum nanobiocomposites-doped polypyrrole film by Longhua Tang; Yihua Zhu; Xiaoling Yang; Chunzhong Li (pp. 145-150).

An enhanced amperometric biosensor based on incorporating one kind of unique nanobiocomposite as dopant within an electropolymerized polypyrrole film has been investigated. The nanobiocomposite was synthesized by self-assembling glutamate dehydrogenase (GLDH) and poly(amidoamine) dendrimer-encapsulated platinum nanoparticles (Pt-DENs) onto multiwall carbon nanotubes (CNTs). ζ-Potentials and high-resolution transmission electron microscopy (HRTEM) confirmed the uniform growth of the layer-by-layer nanostructures onto the carboxyl-functionalized CNTs. The size of Pt nanoparticles is approximately 3nm. The (GLDH/Pt-DENs)_n/CNTs/Ppy hybrid film was obtained by electropolymerization of pyrrole onto glassy carbon electrodes and characterized with scanning electron microscopy (SEM), cyclic voltammetry (CV) and other electrochemical measurements. All methods indicated that the (GLDH/Pt-DENs)_n/CNTs nanobiocomposites were entrapped within the porous polypyrrole film and resulted in a hybrid film that showed a high electrocatalytic ability toward the oxidation of glutamate at a potential 0.2V versus Ag/AgCl. The biosensor shows performance characteristics with high sensitivity (51.48μAmM⁻¹), rapid response (within 3s), low detection limit (about 10nM), low level of interference and excellent reproducibility and stability.

Keywords: Carbon nanotubes; Dendrimer-encapsulated platinum nanoparticles; Self-assembly; Polypyrrole; Electropolymerization; Biosensor

Ordered mesoporous polyaniline film as a new matrix for enzyme immobilization and biosensor construction by Qin Xu; Jun-Jie Zhu; Xiao-Ya Hu (pp. 151-156).

Ordered mesoporous polyaniline film has been fabricated by electrodepositing from the hexagonal lyotropic liquid crystalline (LCC). Horseradish peroxidase (HRP), as a symbol biomolecule, was successfully immobilized on the film to construct a new kind of hydrogen peroxide biosensor. The biosensor combined the advantages of the good conductivity of polyaniline and the higher surface area of the ordered mesoporous film. Polyaniline could be served as a wire to relay electron between HRP and the electrode. The high surface area of the film supplied more sites for HRP immobilization, therefore increased the catalytic activity of the biosensor. The ordered mesoporous character of the film increased the rate of mass transport, which resulted in the improvement of sensor response and linearity. The biosensor displayed excellent electrocatalytic response to the detection of H₂O₂ in a concentration range from 1.0μM to 2.0mM with a detection limit of 0.63μM. Good reproducibility, stability, high precision, wide linearity and low detection limit were assessed for the biosensor.

Keywords: Mesoporous; Ordered; Lyotropic liquid crystalline; Biosensor

Membraneless vaporization unit for direct analysis of solid sample by K. Sereenonchai; P. Saetear; N. Amornthammarong; K. Uraisin; P. Wilairat; S. Motomizu; D. Nacapricha (pp. 157-162).

A new apparatus, called ‘membraneless vaporization’ (MBL-VP) unit was designed and developed for direct analysis of solid samples. Solid analyte was converted into a gaseous form which then reacts with an indicator reagent. Change in absorbance was used to quantitate the analyte. Stirring with a magnetic bar was employed to facilitate the evaporation of the gas. Unlike the pervaporation technique, hydrophobic membrane was not required for this MBL-VP technique.Application of the membraneless technique for direct determination of calcium carbonate in calcium supplements, has shown to be very precise (R.S.D.=2.5% for 0.16mmolCO₃²⁻), with detection limit of 0.5mg CaCO₃. Results by this method agreed well with flame atomic absorption spectrometric method. Sample throughput was 20samplesh⁻¹.

Keywords: Membraneless vaporization; Direct analysis; Solid analysis; Carbonate; Carbon dioxide

Use of liposomes to evaluate the role of membrane interactions on antioxidant activity by Marlene Lúcio; Helena Ferreira; José L.F.C. Lima; Salette Reis (pp. 163-170).

In this study the possibility of using liposomes as membrane mimetic systems was evaluated to estimate the antioxidant properties of oxicams and establish a relationship between the interactions of the drugs with the membrane and their consequent antioxidant activity. Different experiments were performed covering the study of the protective effect of oxicams in lipid peroxidation induced by the peroxyl radical (ROO) derived from 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) and using two fluorescence probes with distinct lipophilic properties. Lipid peroxidation using the hydrophilic probe fluorescein was evaluated in lipid and aqueous media. Lipid systems labelled with the fluorescent probe diphenylhexatriene propionic acid (DPH-PA) were used to assess the effects of the drugs on membrane peroxidation simultaneously by fluorescence intensity decay and changes in membrane fluidity by steady-state anisotropy measurements. The use of different probes and liposomes as membrane mimetic systems allowed to conclude that membrane lipoperoxidation is related not only to the scavenging characteristics of the antioxidants but also to their ability to interact with the lipid bilayers.

Keywords: Liposomes; Membrane models; Oxicams; Lipid peroxidation

Determination of fluoride and oxalate using the indicator reaction of Zr(IV) with methylthymol blue adsorbed on silica gel by Olga A. Zaporozhets; Lyudmila Ye Tsyukalo (pp. 171-177).

Solid-phase spectrophotometric and visual test-methods of fluoride and oxalate determination are proposed. The methods are based on the competitive reactions of ZrOCl₂ with methylthymol blue immobilized on silica gel and fluoride or oxalate in solution. Absorbance of the solid-phase reagent at 590nm decreases with the growth of fluoride and oxalate contents in solution. The developed methods demonstrate high selectivity. The interference of Bi(III) and SO₄²⁻, PO₄³⁻ is eliminated by the addition of 0.01molL⁻¹ solution of ascorbic acid and 0.01molL⁻¹ of BaCl₂, respectively. To eliminate the fluoride interference with oxalate determination 1×10⁻³molL⁻¹ solution of Ca(NO₃)₂ at pH 1.5 was added. The anions of the organic acids were destructed prior to F⁻ determination by ultrasonic exposition (44kHz, intensity of ≤10Wcm⁻² for 3min). The proposed methods were applied to the analysis of mineral water, toothpaste and biological fluids.

Keywords: Fluoride and oxalate determination; Solid-phase spectrophotometry; Test kits; Immobilization; Water; Toothpaste; Biological fluids

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Analytica Chimica Acta (v.597, #1)

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Analytica Chimica Acta (v.597, #1)