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Analytica Chimica Acta (v.597, #2)

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

Contents (pp. iii-iv).

Box-Behnken design: An alternative for the optimization of analytical methods by S.L.C. Ferreira; R.E. Bruns; H.S. Ferreira; G.D. Matos; J.M. David; G.C. Brandão; E.G.P. da Silva; L.A. Portugal; P.S. dos Reis; A.S. Souza; W.N.L. dos Santos (pp. 179-186).

The present paper describes fundamentals, advantages and limitations of the Box-Behnken design (BBD) for the optimization of analytical methods. It establishes also a comparison between this design and composite central, three-level full factorial and Doehlert designs. A detailed study on factors and responses involved during the optimization of analytical systems is also presented. Functions developed for calculation of multiple responses are discussed, including the desirability function , which was proposed by Derringer and Suich in 1980. Concept and evaluation of robustness of analytical methods are also discussed. Finally, descriptions of applications of this technique for optimization of analytical methods are presented.

Keywords: Box-Behnken design; Multivariate optimization; Experimental design; Analytical methods; Desirability function; Robustness

Liquid chromatography–electrothermal atomic absorption spectrometry for the separation and preconcentration of molybdenum in milk and infant formulas by I. López-García; P. Viñas; R. Romero-Romero; M. Hernández-Córdoba (pp. 187-194).

Two procedures for the electrothermal atomic absorption spectrometric determination of molybdenum in milk and infant formulas using slurried samples are described. For powdered milk samples, 10% (m/v) slurries were prepared in a medium containing 25 and 75% (v/v) concentrated hydrogen peroxide and hydrofluoric acid, respectively, and introduced directly into the furnace. Palladium (200μgmL⁻¹) was used as the modifier and calibration was carried out using aqueous standards prepared in the same medium. The detection limit was 0.02μgg⁻¹ for powdered milk samples suspended at 10% (m/v) (equivalent to 2μgL⁻¹). The relative standard deviation (R.S.D.) for five measurements was 1.9%, the characteristic mass being 25pg. For liquid milk samples, a procedure was proposed based on preconcentration and removal of the matrix, using ionic exchange (Amberlite IRA 743) and elution of molybdenum with 5% (m/v) NaOH. In this case, a 30-fold improvement in the calibration slope was achieved, leading to a detection limit of 0.04μgL⁻¹ for liquid samples diluted to 10%. The R.S.D. was 3.5%. Using a size-based separation procedure, it was found that molybdenum is present in its inorganic form or associated to low molecular weight substances in cow milk, while in breast milk it is associated to proteins. The reliability of the procedure was checked by comparing the results obtained with those found using a previous mineralization stage and by analyzing three certified reference materials, namely, BCR 063R (skim milk powder), NBS 1549 (non-fat milk powder) and NBS 8435 (whole milk powder).

Keywords: Electrothermal atomic absorption spectrometry; Liquid chromatography; Molybdenum; Speciation; Milk; Infant formula

Determination of depleted uranium in fish by S. D’Ilio; N. Violante; O. Senofonte; F. Petrucci (pp. 195-202).

Depleted uranium (DU) is a by-product of the uranium enrichment process for nuclear fuel. According to the Commission Decision 2002/657/EC, a confirmatory method for the quantification of DU in freeze-dried fish was developed by isotope ratio dynamic reaction cell inductively coupled plasma-mass spectrometry (IR-DRC-ICP-MS). A preliminary study was performed to determine the following parameters: instrumental detection limit (IDL), isotopic ratio measurement limit (IRML), percentage of DU (P_DU) in presence of natural uranium (NU) and limit of quantification (LoQ_DU). The analyses were carried out by means of IR-DRC-ICP-MS. Ammonia was the reaction gas used for the dynamic reaction cell. In addition, a sector field inductively coupled plasma mass spectrometer (SF-ICP-MS) was employed to calculate the within-laboratory reproducibility. For the confirmatory method the following parameters were determined: (a) trueness; (b) precision; (c) critical concentrations alpha and beta (CC_α, CC_β); (d) specificity; (e) stability. Trueness was assessed by using the recovery tests. The recovery and within-laboratory reproducibility were determined by fortifying the blank digested solution of dogfish tissue: six aliquots were fortified at 1, 1.5 and 2 times the LOQ_DU with 25.0, 37.5 and 50.0ngL⁻¹ or 4.16, 6.24, 8.32μgkg⁻¹ with a recovery of −8.2, +9.5 and +9.6%, respectively and a within-laboratory reproducibility (three analytical run) of 15.5, 8.0 and 11.0%, respectively. The results for the decision limit and the detection capability were: CC_α=11.69ngL⁻¹ and CC_β=19.8ngL⁻¹. The digested solutions resulted to be stable during testing time (60 days) and the method can be considered highly specific as well.

Keywords: Depleted uranium; Inductively coupled plasma mass spectrometry; Isotopic ratio measurements; Validation of methods; Long-lived radionuclide

Evolving Window Zone Selection method followed by Independent Component Analysis as useful chemometric tools to discriminate between grapefruit juice, orange juice and blends by M. Cuny; G. Le Gall; I.J. Colquhoun; M. Lees; D.N. Rutledge (pp. 203-213).

This study investigates the use of high resolution¹H NMR as a suitable alternative to the standard chromatographic method for the determination of adulteration of orange juice ( Citrus sinensis) with grapefruit juice ( Citrus paradisi) based on flavonoid glycoside content. Fifty-nine orange juices (OJ), 23 grapefruit juices (GJ) and 10 blends (OG), obtained from local retail outlets were used to assess the performance of the¹H NMR method. The work presented here introduces the Evolving Window Zone Selection (EWZS) function that holds promise for the automatic detection of spectral regions tailored to discriminate predefined groups. This technique was applied on the pre-processed¹H NMR spectra of the 92 juices. Independent Component Analysis (ICA) is a good alternative to Principal Component Analysis (PCA) for recovering linearly-mixed unobserved multidimensional independent signals and has been used in this study to build supervised models that classify the samples into three categories, OJ, GJ, OG. The regions containing the known flavonoid glycoside markers were selected as well as another zone containing the signals of sucrose, α-glucose and other components that were tentatively attributed. ICA was applied on three different groups of selected variables and showed good results for both discrimination and interpretation of the signals. Up to 97.8% of the juices were correctly attributed. This method gave better results than the commonly used PCA method. In addition, the time required to carry out the¹H NMR analysis was less than half the time of the standard chromatographic method.

Keywords: Fruit juice; Orange; Grapefruit; ¹; H NMR spectroscopy; Authenticity; Chemometric analysis; Evolving Window Zone Selection; Independent Component Analysis

Quantitative structure–property relationship studies for collision cross sections of 579 singly protonated peptides based on a novel descriptor as molecular graph fingerprint (MoGF) by Peng Zhou; Feifei Tian; Zhiliang Li (pp. 214-222).

Aiming at ion mobility spectrometry (IMS), computer-assisted ion mobility prediction (CAIMP) has been recently developed to simulate and predict diverse IMS behaviors in assistance of mathematics and computer science. Of that, quantitative structure–property relationship (QSPR) plays a vital role, dedicating to predict properties of unknown samples by creating statistical model based on known samples. In QSPR, the key lies in how to transform structural characteristics of target compounds into a group of numerical codes. In consideration that future IMS applications may mainly focus on intricate drug/biological systems, a novel molecular structural characterization method referring to molecular graphic fingerprint (MoGF) is proposed in this paper. In MoGF approach, radical distribution function is employed to map intrinsic interatomic correlations into a coordinate system according to a reasonable sampling interval, thus forming the characteristic graph curve which is rich in information on molecular structural characteristics, possessing of great merits in easy calculation, independent of experiments, large information contents, explicit structural meanings and intuitive expressions, etc. Consequently, MoGF is utilized to QSPR studies on 579 singly protonated peptide collision cross sections, and the constructed partial least square (PLS) regression model is confirmed to be robust and predictable by rigorous both internal and external validations, with statistics as r²=0.991, q²=0.990, RMSEE=5.526, RMSCV=5.572,qext2=0.990,rext2=0.990,r0,ext2=0.990,r0,ext'2=0.990, k=1.003, k′=0.996 and RMSEP=5.561, respectively.

Keywords: Ion mobility spectrometry; Computer-assisted ion mobility prediction; Quantitative structure–property relationship; Molecular structural characterization; Molecular graph fingerprint; Peptide

Polymer coated quartz crystal microbalance sensors for detection of volatile organic compounds in gas mixtures by Pengchao Si; John Mortensen; Alexei Komolov; Jens Denborg; Preben Juul Møller (pp. 223-230).

By coating different conducting polymers of thiophene and its derivatives on quartz crystal microbalance (QCM) sensor surfaces, new novel QCM gas sensors have been produced in two simple ways, which could classify testing gas samples of volatile organic compounds (VOCs) gases. Principle components analysis (PCA) has been performed based on the QCM measurement results, which shows that our QCM sensors array has very good utilizing potential on sensing both polar and low-polar/nonpolar VOC gases. The sensitivity, selectivity, reproducibility and detection limit of QCM sensors have also been discussed. Quantitative variation of sensitivity response with the increasing concentration has been studied. (PLS) analysis and prediction of concentrations of single gas in mixtures have been carried out.

Keywords: Quartz crystal microbalance; Volatile organic compounds; Conducting polymer; Polythiophene; Multi sensor system; Electronic nose; Principle components analysis; Partial least square

Characterization of an ion-selective polypyrrole coating and application to the joint determination of potassium, sodium and ammonium by electrochemical impedance spectroscopy and partial least squares method by Montserrat Cortina-Puig; Xavier Muñoz-Berbel; Manuel del Valle; Francisco J. Muñoz; M. Asunción Alonso-Lomillo (pp. 231-237).

A stable immobilization of ionophores (INPHs) was achieved by selectively electropolymerizing overoxidized pyrrol on the working electrode surface. The optimal conditions found allowed the immobilization of a huge amount of INPH which remained its recognition properties. A single sensing chip, containing a generic INPH or an INPH mixture, was employed to the joint quantification of potassium, ammonium and sodium in fertilizer samples. Electrochemical impedance spectroscopy (EIS) and partial least square (PLS) regression were used to obtain and process the data, respectively. The sensing element (INPH) and the exposure time were optimized. The best results were obtained by using the dibenzo-18-crown-6 INPH after waiting for 60s, the time required to stabilize the impedimetric measurement. Taking into account that a single chip was employed, acceptable relative errors were obtained in the determination of potassium and ammonium (17% and 9%, respectively) in real fertilizer samples, also containing sodium. Although sodium concentration could not be estimated with precision, it had to be introduced into the calibration set data in order to model its interference with the other two ions.

Keywords: Ionophore-polypyrrole modified chip; Partial least squares; Electronic tongue; Impedance measurements

Effects of microstructure of carbon nanofibers for amperometric detection of hydrogen peroxide by Zhizhou Li; Xiaoli Cui; Junsheng Zheng; Qingfei Wang; Yuehe Lin (pp. 238-244).

Carbon nanofibers (CNFs) with three microstructures, including platelet-carbon nanofibers (PCNFs), fish-bone-carbon nanofibers (FCNFs), and tube-carbon nanofibers (TCNFs), were synthesized, characterized, and evaluated for electrochemical sensing of hydrogen peroxide. The CNFs studied here show microstructures with various stacked morphologies. The sizes and graphite-layer ordering of the CNFs can be well controlled. Glassy carbon (GC) electrodes modified by CNFs were fabricated and compared for amperometric detection of hydrogen peroxide. Sensors based on PCNFs/GC, FCNFs/GC, and TCNFs/GC were used in the amperometric detection of H₂O₂ in solution by applying a potential of +0.65V versus Ag/AgCl at the working electrode. The highest electrocatalytic performance was observed for PCNFs/GC among the three types of hydrogen peroxide sensors. The amperometric response of PCNFs/GC retained over 90% of the initial current of the first day up to 21 days. The linear range is from 1.80×10⁻⁴ to 2.62×10⁻³M with a correlation coefficient larger than 0.999 and with a detection limit of 4.0μM H₂O₂ (S/N=3). The relative standard deviation for detecting 1.80×10⁻⁴M H₂O₂ ( N=8) is 2.1% with an average response of 0.64μA. The significant diversity of electrocatalytic activity of the CNFs toward the oxidation of hydrogen peroxide may result from the difference of morphologies, textural properties, and crystalline structures.

Keywords: Carbon nanofibers; Hydrogen peroxide oxidation; Electrocatalytic activity; Hydrogen peroxide sensors

Characterization of surfactant/hydrotalcite-like clay/glassy carbon modified electrodes: Oxidation of phenol by María Hernández; Lenys Fernández; Carlos Borrás; Jorge Mostany; Hermes Carrero (pp. 245-256).

The characteristics of hydrotalcite (HT)-like clay films containing ionic and nonionic surfactants and their ability to oxidize phenol have been examined. The HT clay (Co/Al–NO₃) was synthesized by coprecipitation techniques and then modified with surfactants such as sodium dodecylbenzenesulfonate (SDBS), octylphenoxypolyethoxyethanol (TX100) or cetylpyridinium bromide (CPB). X-ray diffraction analysis revealed that the interlayer basal spacing varied depending on the type of surfactant retained by the HT. The presence of SDBS and CPB expanded the HT interlayer, which in the presence of TX100 did not show an appreciable change. Phenol oxidation is favored at surfactant-HT-GC modified electrodes, after a preconcentration time, compared to phenol oxidation at HT-GC or GC electrodes. Surfactant-HT-GC modified electrodes display good stability in continuous electrochemical phenol oxidation. At pH values between 6 and 10.8, both SDBS-HT-GC and TX100-HT-GC modified electrodes seem to be promising electrodes for the detection of phenol in water; while the CPB-HT-GC modified electrode should be affected by the inorganic anions.

Keywords: Synthetic hydrotalcite-like clay; Phenol oxidation; Clay-modified electrode

Screening of variety- and pre-fermentation-related volatile compounds during ripening of white grapes to define their evolution profile by Elisabete Coelho; Sílvia M. Rocha; António S. Barros; Ivonne Delgadillo; Manuel A. Coimbra (pp. 257-264).

The variety- and pre-fermentation-related volatile compounds of ‘Fernão-Pires’ (FP) white grape berries were analyzed during ripening by headspace-solid phase microextraction (HS-SPME) coupled to gas chromatography-quadrupole mass spectrometry (GC-qMS). A preliminary step, in which the grapes were crushed and macerated before HS-SPME analyses, was used. The sampling started at véraison (beginning of berry ripening) and was carried on during 5 weeks in two different vineyards. Sixteen terpenoids, two C₁₃ norisoprenoids, two aromatic alcohols, two C₆ aldehydes, and three C₆ alcohols were identified. The amount of all volatiles increased since véraison towards day 20. A sharp decrease was observed after this day. The maximum amount of varietal volatile compounds was coincident with the harvesting day for white table wine production defined by the ratio sugar/acid content. The varietal volatile evolution observed for FP grapes shows that the maximum amount of volatiles occurs only in a very short period. As a consequence, the establishment of the optimum moment for harvesting of FP white variety, based on its volatile content, deserves higher accuracy than that necessary for all other already studied grapes. This work also evidences that the analysis of the evolution of the terpenoids with higher GC peak area can represent the evolution of all varietal compounds. For FP grapes, this work shows that the screening of linalool, α-terpineol, and geraniol during ripening can be used to define the evolution profile of the varietal volatile compounds.

Keywords: Vitis vinifera; L.; Fernão-Pires; Varietal volatiles; Pre-fermentation-related volatiles; Ripening; Maturity; Headspace-solid phase microextraction

Ultrasound-assisted extraction of isoflavones from soy beverages blended with fruit juices by Mauricio A. Rostagno; Miguel Palma; Carmelo G. Barroso (pp. 265-272).

A new method for the fast determination of isoflavones from soy beverages blended with fruit juices without the need of freeze-drying the sample was developed. During the method development, several parameters were studied: solvent (methanol and ethanol), sample:solvent ratio (5:1 to 0.2:1), temperature (10–60°C) and extraction time (5–30min). The most important parameter for the extraction of isoflavones from soy drinks was the sample:solvent ratio. The optimized method consists of extracting the sample with ethanol with a sample:solvent ratio of 0.2:1 on an ultrasound bath at 45°C during 20min. Also, samples were freeze-dried, extracted using conventional method and compared with the optimized method and no significant difference was observed on total and individual isoflavone concentration. The most representative samples from the Spanish market, with a wide variation of isoflavone concentration were analyzed using the optimized method. Differences between manufacturers reached an almost 10 times fold variation. Overall isoflavone concentration ranged from 6.7 to 58.2mgL⁻¹.

Keywords: Isoflavones; Fast analysis; Ultrasound-assisted extraction; Soy beverages

Optimization of a novel method for the organic chemical characterization of atmospheric aerosols based on microwave-assisted extraction combined with stir bar sorptive extraction by O. Alvarez-Avilés; L. Cuadra-Rodríguez; F. González-Illán; J. Quiñones-González; O. Rosario (pp. 273-281).

A practical analytical methodology based on coupling microwave-assisted extraction–stir bar sorptive extraction–thermal desorption-gas chromatography–mass spectrometry (MAE–SBSE–TD–GC–MS) was developed and validated for the characterization of several SVOC in atmospheric particulate matter (PM).The high enrichment capacity of SBSE makes it a powerful tool for improving detection limits and MAE has been useful for overcoming the long extraction times and high volumes of extraction solvent used in traditional methodologies. Relative to Soxhlet extraction followed by GC–MS analysis (EPA Methods 3540 and 8270C), the MAE–SBSE–TD–GC–MS methodology resulted with approximately 10⁴ times better detection limits. Detection limits ranged from 0.3 to 8.3pgm⁻³ for pp′-DDD and decachlorobyphenyl, respectively in PM2.5, 24m³ air sample. The performance of the optimized methodology gave good precisions, with R.S.D. less than 30% for most of the standards, and linearity within the range tested of 0.1–15μgL⁻¹. Analysis of real PM samples resulted in the identification of compounds in the ngL⁻¹ range.

Keywords: Particulate matter; Microwave-assisted extraction; Stir bar sorptive extraction; Thermal desorption; Organic aerosols

Quantitative analysis of clavulanic acid in porcine tissues by liquid chromatography combined with electrospray ionization tandem mass spectrometry by Tim Reyns; Sandra De Boever; Siegrid De Baere; Patrick De Backer; Siska Croubels (pp. 282-289).

The purpose of this study was to develop and validate a method for the determination of clavulanic acid (CLAV) residues in edible tissues of swine by liquid chromatography-electrospray ionisation-tandem mass spectrometry (LC-ESI-MS/MS). After a simple extraction of CLAV using an aqueous phosphate buffer solution of pH 6.0, an ultrafiltration step was performed for protein removal. Chromatography of CLAV and the internal standard tazobactam (TAZO) was achieved on a reversed-phase PLRP-S polymeric column (150mm×2.1mm i.d., 100Å) using a mixture of 0.05 (v/v)% formic acid in water and acetonitrile. The mass spectrometer was operated in the MS/MS selected reaction monitoring (SRM) mode. The method was validated for the analysis of porcine muscle, skin plus fat, liver and kidney, according to the requirements defined by the European Community. Calibration curves were prepared for all tissues and good linearity was achieved over the concentration ranges tested (correlation coefficient ≥0.99 and goodness-of-fit coefficient ≤10%). Limits of quantification of 50ngg⁻¹ were obtained for the analysis of CLAV in the various tissues which corresponds in all cases to at least half the maximum residue limits (MRLs). Limits of detection ranged between 8.0 and 15.14ngg⁻¹. The within-day, between-day precisions and trueness fell within the ranges specified in the EMEA/CVMP/573-00/FINAL document. Biological samples from pigs that received an oral or intravenous bolus of a commercial amoxicillin/clavulanic acid formulation were analyzed using the described method.

Keywords: Clavulanic acid; Residue analysis; Liquid chromatography–tandem mass spectrometry; Porcine tissues; Validation

Determination of phosphate using a highly sensitive paired emitter–detector diode photometric flow detector by Martina O’Toole; King Tong Lau; Roderick Shepherd; Conor Slater; Dermot Diamond (pp. 290-294).

The use of a novel inexpensive photometric device, a paired emitter–detector diode (PEDD) has been applied to the colorimetric determination of phosphate using the malachite green spectrophotometric method. The novel miniaturized flow detector applied within this manifold is a highly sensitive, low cost, miniaturized light emitting diode (LED) based detector. The optical flow cell was constructed from two LEDs, whereby one is the light source and the second is the light detector, with the LED light source forward biased and the LED detector reversed biased. The photocurrent generated by the LED light source discharges the junction capacitance of the detector diode from 5V (logic 1) to 1.7V (logic 0) and the time taken for this process to occur is measured using a simple timer circuit.The malachite green (MG) method employed for phosphate determination is based on the formation of a green molybdophosphoric acid complex, the intensity of which is directly related to phosphate concentration. Optimum analytical parameters such as reaction kinetics, reagent to sample concentration ratio and emitter wavelength intensity were investigated for the spectrophotometric method. Linear calibration plots that obeyed the Beer–Lambert law were obtained for phosphate in the range of 0.02–2μM. The dynamic range, sensitivity and limits of detection are reported.

Keywords: Light emitting diode detector; Malachite green; Phosphate; Colorimetric flow analysis

Spectrophotometric determination of carbon tetrachloride via ultrasonic oxidation of iodide accelerated by dissolved carbon tetrachloride by Rong Zhou; Wei Luo; Lihua Zhu; Fang Chen; Heqing Tang (pp. 295-299).

Ultrasonic oxidation of iodide was investigated in the presence of carbon tetrachloride (CCl₄). The ultrasonic oxidation of potassium iodide led to formation of iodine and then I₃⁻ in the presence of excess iodide, and the generated I₃⁻ shows strong UV absorption with a molar absorptivity of 2.31×10⁴Lmol⁻¹cm⁻¹ at the maximum absorption wavelength of 351nm. The ultrasonic oxidation of iodide was found to be significantly promoted by a small addition of CCl₄, and it was further found that the generation rate was increased with the amount of CCl₄ added. This can be used to analyze the level of CCl₄ dissolved in aqueous solutions. Under optimum conditions, the concentration of generated iodine (or its absorption at 351nm) was found to correlated linearly with the concentration of CCl₄ in the range of 0.2–50mgL⁻¹ (detection limit=0.09mgL⁻¹, R²=0.999). As an alternative indirect spectrophotometric method of CCl₄ determination, the proposed method was successfully applied to determine the concentrations of CCl₄ in several practical samples, showing merits of being sensitive and simple of operation.

Keywords: Carbon tetrachloride determination; Spectrophotometric; Ultrasonic oxidation; Iodide

Resonance scattering method for the ultrasensitive determination of peptides using semiconductor nanocrystals by Xudong Chen; Yeping Dong; Li Fan; Dacheng Yang; Mingqiu Zhang (pp. 300-305).

Resonance light scattering (RLS) of the functionalized ZnS nanocrystals–peptides system and its analytical application have been studied. The RLS intensity can be efficiently enhanced when various peptides were added. The mechanism of the RLS enhancement of ZnS nanocrystals was discussed. The change of RLS intensity was in proportion to the concentration of peptides. The limits of detection were in range of 2.8–5.7ngmL⁻¹. Application results to synthetic samples showed simplicity, rapidity, high sensitivity and satisfactory reproducibility of the presented method. Measurements of real samples also give satisfactory results which were in good agreement with those obtained using high performance liquid chromatography (HPLC) and liquid chromatography–mass spectrography (LC–MS) methods.

Keywords: Peptides; Nanocrystals; Resonance light scattering; Determination

Tracking of mercury ions in living cells with a fluorescent chemodosimeter under single- or two-photon excitation by Zhou-Jun Lu; Pei-Nan Wang; Yu Zhang; Ji-Yao Chen; Shen Zhen; Bing Leng; He Tian (pp. 306-312).

Tracking of Hg²⁺ in solutions as well as in living cells was conducted with a fluorescent chemodosimeter by measuring the spectral shift of its fluorescence under single- or two-photon excitation. The spectral hypsochromic shifts of this chemodosimeter when reacting with Hg²⁺ were found to be about 50nm in acetonitrile/water solutions and 32nm in Euglena gracilis 277 living cells. This chemodosimeter shows high sensitivity and selectivity, and is not influenced by the pH values. It can signal Hg²⁺ in solutions down to the ppb range under either single-photon excitation (SPE) at 405nm or two-photon excitation (TPE) at 800nm. However, with low cellular chemodosimeter concentrations, the SPE spectra were disturbed by the auto-fluorescence from the native fluorophore in the cell, while the TPE spectra were still of high quality since the two-photon absorption cross section of this chemodosimeter is much larger than that of the native fluorophores in the cell.

Keywords: Fluorescent chemodosimeter; Mercury ion; Living cell; Two-photon excitation

Development of miniaturized pH biosensors based on electrosynthesized polymer films by Olivier Segut; Boris Lakard; Guillaume Herlem; Jean-Yves Rauch; Jean-Claude Jeannot; Laurent Robert; Bernard Fahys (pp. 313-321).

A new type of pH biosensor was developed for biological applications. This biosensor was fabricated using silicon microsystem technology and consists in two platinum microelectrodes. The first microelectrode was coated by an electrosynthesized polymer and acted as the pH sensitive electrode when the second one was coated by a silver layer and was used as the reference electrode. Then, this potentiometric pH miniaturized biosensor based on electrosynthesized polypyrrole or electrosynthesized linear polyethylenimine films was tested. The potentiometric responses appeared reversible and linear to pH changes in the range from pH 4 to 9. More, the responses were fast (less than 1min for all sensors), they were stable in time since PPy/PEI films were stable during more than 30 days, and no interference was observed. The influence of the polymer thickness was also studied.

Keywords: Electrochemistry; pH biosensor; Microsystem technology; Polypyrrole; Linear polyethylenimine

Ytterbium-selective polymeric membrane electrode based on substituted urea and thiourea as a suitable carrier by A.K. Singh; A.K. Jain; Sameena Mehtab (pp. 322-330).

Plasticized membranes using 1-phenyl-3-(2-thiazolyl)-2-thiourea (PTT) and 1-phenyl-3-(2-thiazolyl)-2-urea (PTU) have been prepared and explored as ytterbium ion-selective sensors. Effect of various plasticizers, viz. chloronaphthalene (CN), o-nitrophenyloctyl ether ( o-NPOE), dibutylphthalate (DBP), dioctylsebacate (DOS) and anion excluders, sodium tetraphenylborate (NaTPB) and oleic acid (OA) was studied and improved membrane performance was observed. Optimum performance was noted with membrane of PTT having composition of PTT (3.5):PVC (80):DOS (160):NaTPB (1.5) in mg. The sensor works satisfactorily in the concentration range 1.2×10⁻⁷ to 1.0×10⁻²M (detection limit 5.5×10⁻⁸M) with a Nernstian slope of 19.7mVdecade⁻¹ of activity. Wide pH range (3.0–8.0), fast response time (10s), non-aqueous tolerance (up to 20%) and adequate shelf life (12 weeks) indicate the vital utility of the proposed sensor. The proposed electrode comparatively shows good selectivity for Yb³⁺ ion with respect to alkali, alkaline earth, transition and rare earth metals ions and can be used for its determination in binary mixtures and sulfite determination in white and red wine samples.

Keywords: Ion-selective electrode; Urea and thiourea derivatives; Ytterbium; Neutral carrier

Fully automated immunoassay for detection of prostate-specific antigen using nano-magnetic beads and micro-polystyrene bead composites, ‘Beads on Beads’ by Tadashi Matsunaga; Yoshiaki Maeda; Tomoko Yoshino; Haruko Takeyama; Masaaki Takahashi; Harumi Ginya; Junko Aasahina; Hideji Tajima (pp. 331-339).

Magnetic beads have served as a conventional bioassay platform in biotechnology. In this study, a fully automated immunoassay was performed using novel nano- and microbead-composites constructed by assembling nano-magnetic beads onto polystyrene microbeads, designated ‘Beads on Beads’. Nano-sized bacterial magnetic particles (BacMPs) displaying the immunoglobulin G (IgG)-binding domain of protein A (ZZ domain) were used for the construction of ‘Beads on Beads’ via the interaction of biotin–streptavidin. The efficient assembly of ‘Beads on Beads’ was performed by gradual addition of biotin-labeled BacMPs onto streptavidin-coated polystyrene microbeads. Approximately 2000 BacMPs were uniformly assembled on a single microbead without aggregation. The constructed ‘Beads on Beads’ were magnetized and separated from the suspension by using an automated magnetic separation system with a higher efficiency than BacMPs alone. Furthermore, fully automated detection of prostate-specific antigens was performed with the detection limit of 1.48ngmL⁻¹. From this preliminary assay, it can be seen that ‘Beads on Beads’ could be a powerful tool in the development of high-throughput, fully automated multiplexed bioassays.

Keywords: Fully automated immunoassay; Prostate-specific antigen; Bacterial magnetic particle; Polystyrene microbeads

Characterization of flavor compounds in Chinese liquor Moutai by comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry by Shukui Zhu; Xin Lu; Keliang Ji; Kunliang Guo; Yanli Li; Caiying Wu; Guowang Xu (pp. 340-348).

In this paper, a method to characterize the volatile compounds in Chinese liquors by comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry has been developed. The selection of column combination and the optimization of temperature program are discussed. With the optimized conditions, ordered chromatograms are achieved in the two-dimensional plane, which is useful for the identification of unknown compounds. According to the automated data processing by TOFMS software, combining with the ordered chromatogram and the retention index database developed by our group, a total of 528 components are identified in a Moutai liquor sample, including organic acids, alcohols, esters, ketones, aldehydes, acetals, lactones, nitrogen-containing and sulfur-containing compounds, etc. In addition, the contribution of some important aroma compounds to flavor of Moutai liquor has also been studied.

Keywords: Comprehensive two-dimensional gas chromatography; Time-of-flight mass spectrometry; Chinese liquor; Moutai; Flavor compounds

Fiber optic-linear array detection spectrophotometry in combination with dispersive liquid–liquid microextraction for simultaneous preconcentration and determination of palladium and cobalt by N. Shokoufi; F. Shemirani; Y. Assadi (pp. 349-356).

A new combined method including fiber optic-linear array detection spectrophotometry (FO-LADS) and dispersive liquid–liquid microextraction (DLLME) was developed using a cylindrical micro-cell for simultaneous preconcentration and determination of different species. DLLME and FO-LADS methods have good matching conditions for being combined since FO-LADS is a suitable method for the determination of analytes in low volume of the remained phase obtained after DLLME.DLLME technique was successfully used as a sample preparation method. In this preconcentration method, an appropriate mixture of ethanol (the disperser solvent) and 1,2-dichlorobenzene (the extraction solvent) was injected rapidly into the water sample containing palladium and cobalt after complex formation using 1-(2-pyridylazo)-2-naphthol (PAN) reagent. After phase separation, 50μL of the sedimented phase containing enriched analytes was determined by FO-LADS. The ordinary and first derivative absorption spectra were obtained for optimization and simultaneous determination of palladium and cobalt, respectively.Under the optimum conditions, the calibration graphs were linear in the range of 2–100μgL⁻¹ and 1–70μgL⁻¹ with detection limit of 0.25μgL⁻¹ and 0.2μgL⁻¹ for palladium and cobalt, respectively. The relative standard deviations (R.S.D.s, n=5) were lower than 4%. The enhancement factors of 162 and 165 were obtained for palladium and cobalt, respectively.The proposed method was compared with other methods and applied to the analysis of several real and synthetic samples with satisfactory results.

Keywords: Linear array detector; Dispersive liquid–liquid microextraction; Optical fiber; Palladium; Cobalt

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Analytica Chimica Acta (v.597, #2)

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Analytica Chimica Acta (v.597, #2)