Analytica Chimica Acta (v.459, #1)

Calendar (N1-N3).

Lithium sensor based on the laser scanning semiconductor transducer by Yu. Ermolenko; T. Yoshinobu; Yu. Mourzina; K. Furuichi; S. Levichev; Yu. Vlasov; M.J. Schöning; H. Iwasaki (1-9).
A lithium-selective polymeric membrane has been immobilised on the surface of a semiconductor transducer. This light-addressable potentiometric sensor (LAPS) with the induced lithium selectivity has been prepared with the aim at further development of a Li+ assay in liquid media, including biological fluids. The sensor developed exhibits Nernstian response interval of 10−5 to 10−1  mol l−1 with an ionic sensitivity of (58±1) mV/pLi. The detection limit was found to be (3±1)×10−6  mol l−1 Li+. The sensor has high selectivity for lithium over sodium and potassium ions with selectivity coefficients of K Li/Na POT=(7±2)×10−3 and K Li/K POT=(5±1)×10−3, respectively, and a response time of less than 30 s.
Keywords: Light-addressable potentiometric sensor; Lithium sensitivity; Ionophore; Polymeric membrane;

Chronocoulometric flow-injection analysis with solvent polymeric membrane ion sensors by Concepción Sánchez-Pedreño; Joaquı́n A. Ortuño; Jorge Hernández (11-17).
A method to carry out chronocoulometric measurements with solvent polymeric membrane ion sensors in flow-injection systems has been developed. For this, a double potential step was synchronised to the passage of the sample plug through the detector cell. A four-electrode potentiostat with ohmic drop compensation and a new flow-through cell to incorporate the four-electrode and the membrane were developed. A plasticized poly(vinyl chloride) (PVC) membrane containing TBATBP was used and the procedure was applied to the determination of tetraethyl-ammonium. The effect of the electrochemical and flow-injection variables was studied. In the selected conditions, a linear relationship between the quantity of electricity and tetraethyl-ammonium concentration was obtained in the range 5×10−7–5×10−5  M. The detection limit was 7×10−8  M. Good repeatability and between day reproducibility were obtained. The potential application to other quaternary ammonium ions including acetylcholine was also studied.
Keywords: Chronocoulometry; Flow-injection analysis; Solvent polymeric membrane; Ion sensor; Tetraethyl-ammonium determination;

A novel chemiluminscence (CL) flow-through sensor for pipemidic acid is described. It was based on the sensitizing effect of pipemidic acid on the CL oxidation of sulfite by sodium bismuthate in H2SO4 media. The solid-phase sodium bismuthate was mechanicially immobilized on the sponge rubber inside of the CL flow cell as CL oxidant. The calibration graph is linear in the range 0.1–10 μg/ml with a detection limit of 6.2×10−8  g/ml (3σ). A complete analysis could be performed in 1 min with a relative standard deviation (R.S.D.) of 2.5% for 2 μg/ml pipemidic acid (n=8). This method has been successfully applied to determine pipemidic acid in pharmaceutical preparation.
Keywords: Chemiluminscence; Flow-through sensor; Pipemidic acid; Sodium bismuthate; Solid-phase oxidant;

Differentiation of human serum samples by surface plasmon resonance monitoring of the integral glycoprotein interaction with a lectin panel by Michael Mecklenburg; Juraj Svitel; Fredrik Winquist; Jin Gang; Katharina Ornstein; Estera Dey; Xie Bin; Eva Hedborg; Ragnar Norrby; Hans Arwin; Ingemar Lundström; Bengt Danielsson (25-31).
Bacterial infection and inflammation result in massive changes in serum glycoproteins. These changes were investigated by the interaction of the saccharide glycoprotein moiety with lectins. A panel of eight lectins (Canavalia ensiformis, Bandeiraea simplicifolia BS-I, Arachis hypogaea, Phytolacca americana, Phaseolus vulgaris, Artocarpus integrifolia, Triticum vulgaris and Pisum sativum) was used to differentiate human serum glycoproteins obtained from patients with various bacterial infections. Lectin functionalised sensing layers were created on gold-coated wafers and lectin–glycoprotein interactions were monitored by surface plasmon resonance. The interaction of the lectin panel with serum glycoproteins produces unique patterns. Principal component analysis (PCA) was used to analyse the patterns. The actual panel of eight lectins enabled discrimination between sera obtained from patients sick with bacterial infection and healthy patients. Extended lectin panels have the potential to distinguish between types of bacterial infection and identify specific disease state.
Keywords: Human serum; Bacterial infection; Glycoprotein; Lectin panel; Surface plasmon resonance; Principal component analysis;

An assessment of the toxicity of methyl parathion and products of its photodegradation in water samples was performed using conductometric biosensors based on thin films planar electrodes and immobilized cholinesterases. All photodegradation experiments were carried out using a quartz reaction cell equipped with a 125 W high pressure mercury arc lamp as source of radiation. The photodegradation kinetics can be described as a first-order degradation curve C=C0   e −kt , where C 0=(9.1±0.1)×10−5  M, k=0.026±0.001 min−1 and t 1/2=26 min. The high performance liquid chromatography (HPLC) was used to identify and quantify methyl paraoxon and 4-nitrophenol as main methyl parathion photoproducts. It was shown for the first time by using conductometric enzyme biosensor that the inhibition effect on the acetyl cholinesterase (AcChE) activity increases dramatically as soon as the photodegradation of methyl parathion begins. Methyl paraoxon is about 10 times more toxic than methyl parathion. The toxicity curve does not exactly follow the appearance of methyl paraoxon. The results obtained could be explained by a strong synergistic effect of methyl parathion and methyl paraoxon on the enzyme activity.
Keywords: Conductometric biosensor; Methyl parathion; Photodegradation; Toxicity; Synergistic effect;

Glassy carbon paste electrodes modified with polyphenol oxidase by Marcela C. Rodrı́guez; Gustavo A. Rivas (43-51).
The electrochemical behavior of a glassy carbon paste electrode (GCPE) is evaluated in comparison to that of graphite paste electrode (gPE) and glassy carbon electrode (GCE). Important shifting in the peak potentials and increases in the peak currents for catechol, ascorbic acid, dopamine and hydroquinone were obtained for the GCPE and its usefulness for the development of phenol and catechol biosensors was also evaluated. Both, pure mushroom polyphenol oxidase (PPO) and fresh mushroom tissues were used as biorecognition elements. The effect of the binder percentage in the composite material was also studied. The bioelectrode was used for the determination of dopamine and acetaminophen in pharmaceutical formulations and for the detection of polyphenols in wine and tea. The bioelectrode demonstrated to be very stable as the response remained around 90% after four months at 4 °C.
Keywords: Glassy carbon microparticles; Glassy carbon paste electrode; Composite electrodes; Enzymatic biosensors; Phenol biosensors; Catechol biosensors;

As a sequel to an earlier paper, we have studied the behaviour of 1-fluoropyrene and pyrene in lamp-excited Shpol’skii spectrofluorimetry at 11 K in two different matrices, n-octane and n-hexane, using two different solidification processes. Particular attention is paid to the suitability of 1-fluoropyrene as an internal standard (IS) to correct for different sources of variability. As a demonstration of the applicability of this approach, four polycyclic aromatic hydrocarbons (PAHs; pyrene, chrysene, benzo[a]pyrene and benzo[k]fluoranthene) were determined in a river sediment extract. The results agreed well with those obtained by HPLC with fluorescence detection.
Keywords: PAH; F-PAH; Pyrene; Calibration; Fluorinated analogues;

Selective fluorescence quenching is used to profile polycyclic aromatic hydrocarbons (PAHs) in samples of environmental origin. After separation by high-efficiency capillary liquid chromatography, the PAHs are detected by laser-induced fluorescence spectroscopy. Nitromethane is added to selectively quench the fluorescence of alternant PAHs, whereas diisopropylamine is added to quench nonalternant PAHs. The chromatograms in the absence and presence of fluorescence quenching are evaluated by means of the product moment correlation method to quantify the statistical similarities and differences. This method is demonstrated by application to three samples: a standard mixture of 16 priority pollutants, a coal-derived fluid, and a contaminated soil. The correlation coefficients (r) are typically 0.99 or higher for samples that are identical in origin, 0.90–0.50 for closely related samples, and less than 0.50 for samples that are distinctly unrelated. This method can be used to confirm with high statistical confidence the cause or source of an event with environmental impact, such as an oil leak or spill, contamination or waste by-products from petroleum fuel production and processing, etc.
Keywords: Fluorescence; Fluorescence quenching; Environmental analysis; Polycyclic aromatic hydrocarbons; Nitromethane; Diisopropylamine;

A sensitized and convenient determination of trace Hg(II) with HgI4 2− complex in benzalkonium chloride media has been studied. The UV–VIS spectrum of HgI4 2− complex in benzalkonium chloride solution had higher sensitivity and reproducibility than that in aqueous solution. The HgI4 2− complex in benzalkonium chloride media was very stable at pH 10.0 and could be quantitatively complexed if I was added to the sample solution more than 17 times the moles of Hg(II). The optimum concentration of benzalkonium chloride was 0.07%. The calibration curve of HgI4 2− complex with good linearity (R 2=0.9963) was obtained in 0.07% benzalkonium chloride media. The detection limit was 1.8×10−8  M. Recovery yields of Hg(II) in spiked real and synthetic samples were mostly above 95%. Based on the experimental results, this proposed technique could be applied to the rapid and simple determination of trace Hg(II) in real samples.
Keywords: Mercury; Benzalkonium chloride; Spectrophotometry;

A novel catalytic spectrophotometric method for the determination of superoxide anion radical (O2) and superoxide dismutase (SOD) activity is proposed. The method is based on the coupling reaction of 2,4-dichlorophenol (2,4-DCP) and 4-amino antipyrine in the presence of H2O2, catalyzed by a Schiff base metal complex included by β-cyclodextrin cross-linked polymer (β-CDP) as a mimetic enzyme. The contribution describes the design and synthesis of a novel Schiff base, salicylidene-2-amino-4-phenylthiazole (SAPTS) as well as a series of its metal complexes: M(II)–(SAPTS)2 [M: Cu(II), Co(II), Zn(II), Ni(II)], among which Cu(II)–(SAPTS)2 exhibits efficient horseradish peroxidase-like catalytic activity. Investigations of the optimum reaction conditions, the mechanism, and effects of coexisting substances are presented. The linear calibration range and the detect limit (3σ) of the developed method for superoxide is from 0.0 to 1.0×10−3 and 7.54×10−7  M, respectively. The determinations of SOD activity in human/rat blood, garlic, onion and scallion serve as models for the proposed method. A comparison of the results with established classical analysis is satisfactory.
Keywords: Mimetic enzyme; β-Cyclodextrin cross-linked polymer; Catalytic spectrophotometry; Superoxide anion radical; Superoxide dismutase;

Using Monte Carlo simulation, the geometric and matrix effects on intensity and intensity ratio measured by EPMA were investigated for both synthetic particles and biomass burning particles. Three particulate standards, KCl, K2SO4, KHSO4, were prepared and measured along with biomass burning particles. The modified CASINO program (University of Sherbrooke, Quebec, Canada) at the University of Antwerp, Belgium was used. The relative intensities obtained by the UA version of the CASINO program appear to be in line with those from experiments.The CASINO program and iterative procedures were applied to quantitatively determinate the atomic fraction of K, Cl and S in particulate standard and real samples. After correcting the geometric and matrix effects, the atomic fraction ratio of K to Cl in KCl sample was found to be 1.007±0.025, 0.996±0.013 and 1.011±0.019 for experiments with high voltages of 15, 20 and 25 keV, respectively. The same procedure was also applied to K2SO4 and KHSO4 standard particle sample. The atomic fraction ratio of K to S was 1.945±0.049 (25 keV) for K2SO4 and 1.014±0.072 (20 keV) for KHSO4. These ratios obtained are close to the theoretic values 1 or 2. Reasonable data were obtained for biomass burning particles, indicating that it is possible to perform chemical speciation.
Keywords: Monte Carlo simulation; Electron probe X-ray microanalysis; Biomass burning particles; Speciation analysis;

Outer product analysis of electronic nose and visible spectra: application to the measurement of peach fruit characteristics by Corrado Di Natale; Manuela Zude-Sasse; Antonella Macagnano; Roberto Paolesse; Bernd Herold; Arnaldo D’Amico (107-117).
Visual aspect and aroma are among the most important features of fruit that determine consumer preferences. Electronic nose and spectroscopic techniques have shown positive results in evaluating some basic analytical parameters of fruit and global features such as the cultivar.In this paper, we illustrate and discuss a study aimed at evaluating the improvement derived by the fusion of visible spectra and electronic nose data. These experiments were performed on a population of yellow peaches belonging to two cultivars. Each sample was measured by visible optical spectroscopy and by electronic nose. In addition, a number of reference parameters were also measured by conventional destructive methodologies.Collected data were analysed individually and then fused together in order to classify the two cultivars and to estimate the reference parameters. Data fusion was performed building the outer product matrix for each measurement. The set of matrices was then successively unfolded and analysed by conventional chemometrics tools.Results were improved using outer products, for instance in classification average percentage errors of 25, 10, and 7 for electronic nose, spectra, and outer product, respectively was achieved. Regression analysis provides the evidence of a substantial orthogonal appearance of the datasets, which offer former hidden information on fruit classification.
Keywords: Outer product; Electronic nose; Spectroscopic techniques; Fruits quality;

A method for spectral curve deconvolution is described, evaluated and applied to micellar systems. The technique is based on combination of H-point curve isolation method (HPCIM) and H-point standard addition method (HPSAM). HPCIM is used for extracting the spectrum of solute in micellar pseudophase and HPSAM is used for calculation of equilibrium concentrations of solute in aqueous phase for each sample. The outputs of procedure are spectrum of dye molecules in micellar pseudophase free from contribution of the dye in the aqueous phase, and partition coefficients of considered solutes between micelle and water phase. The effects of noise and extent of solute partitioning on the reliability of the method are evaluated using model data. The applications of the method to the study of interaction of two different solutes, m-cresol purple (m-CP) and Azure C with Brij-35 and 2-amino-cyclopentene-1-dithiocarboxylic acid (ACDA) with cetyltrimethylamonium bromide (CTAB) micellar systems are presented.
Keywords: Micellar systems; HPCIM; HPSAM; Spectral deconvolution;

Characterisation of a wheat straw cell wall residue by various techniques by Patricia Merdy; Emmanuel Guillon; Jacques Dumonceau; Michel Aplincourt (133-142).
Comparative studies using various analytical and spectroscopic techniques have been carried out on three samples of lignin: two samples of natural lignin that have been extracted using different processes, and one sample of synthetic lignin. This paper discusses the general features common to all three kinds of lignin, as well as the differences between, on one hand, the two natural lignins coming from different extraction processes, and, on the other hand, the natural lignins and the synthetic one. The advantages of each technique in explaining the structure of these three different lignins are emphasised.
Keywords: Lignin; Lignocellulosic; NMR; XPS; Thioacidolyse;

In vitro study of experimental factors affecting the microdialysis results by Marı́a Santos Martı́nez Martı́nez; Beatriz Gutiérrez Hurtado; Clara-Isabel Colino Gandarillas; José Martı́nez Lanao; Amparo Sánchez Navarro (143-150).
The aim of the present study was to determine the influence of a series of experimental conditions (probe, perfusate flow rate and the method used to ascertain recovery) as well as the pharmacokinetic variables (concentration and time) on the estimation of the recovery coefficient of microdialysis probes. Two in vitro pharmacokinetic assays were also carried out to compare the results provided by microdialysis and those obtained with traditional sampling. The probes used were made in our laboratory and ciprofloxacin was used as a model compound. The results revealed that in all cases recovery was dependent on the probe and independent of time for a 80 min sampling time period. The effects of concentration on recovery depend on the flow rate; this was not statistically significant for a flow rate of 2 μl/min but an increase in flow rate to 6 μl/min transformed this parameter into a concentration-dependent variable. A decrease in recovery parallel to the increase in flow rate was found, with an exponential relationship between the two variables. Statistically significant differences were also found between the recovery values obtained for direct dialysis (18.44±1.61) and retrodialysis by loss of the analyte of interest (16.79±3.42). The values of the protein binding of ciprofloxacin as calculated by equilibrium dialysis and by microdialysis were similar. Characterization of the in vitro kinetic profile revealed no statistically significant differences for coefficients and exponents obtained by traditional sampling and microdialysis, although the confidence intervals of the curves were wider for microdialysis.
Keywords: Microdialysis methodology; Probe; Recovery; Ciprofloxacin;

A simple, fast and quantitative method was developed for the determination of As(III) and total inorganic arsenic (As (total)) in natural spring and mineral waters using square wave cathodic stripping voltammetry (SWCSV) at a hanging mercury drop electrode (HMDE). In the determination of As(III), pre-concentration was carried out on the electrode from a solution of 1 mol/l HCl in the presence of 45 ppm of Cu(II) at a potential of −0.39 V versus Ag/AgCl, and the deposited intermetallic compound was reduced at a potential of about −0.82 V versus Ag/AgCl. In the determination of As (total) the pre-concentration was carried out in 1 mol/l HCl in the presence of 400 ppm of Cu(II) at a potential of −0.40 V versus Ag/AgCl, and the intermetallic compound deposited was reduced at a potential of about −0.76 V versus Ag/AgCl. For determination of As(III) the quantification limit was 0.2 ppb for a deposition time of 40 s, and the relative standard deviation (R.S.D.) was calculated to be 6% (n=13) for a solution with 8 ppb of As(III). For As (total), the quantification limit was 2 ppb for a deposition time of 3 min, and the R.S.D. was calculated to be 3% (n=10) for a solution with 8 ppb of As(V). The method was validated by application of recovery and duplicate tests in the measurements of As(III) and As (total) in natural spring and mineral waters. For As (total), the results of the SWCSV method were compared with the results obtained by optical emission spectrometry with ICP coupled to hydride generation (OES–ICP–HG) good correlation being observed.
Keywords: Arsenic; Speciation; Stripping voltammetry; HMDE;

Diverse matrix effects on the determination of bismuth, selenium and tellurium (μg g−1) in nickel-based alloys and pure copper by flow-injection hydride generation atomic absorption spectrometry (FIAS-HGAAS) were investigated. Sodium tetrahydroborate was used as the reductant. The separation of analytes from copper matrix was mandatory while the analytes were successfully determined without being separated from the alloy matrix. Hydrochloric acid was effective in the prereduction of bismuth and selenium, however, it did not give any satisfactory result for tellurium in nickel-based alloys. In this work, 5% (w/v) ascorbic acid was proved effective for the prereduction of tellurium.Successful determination of tellurium in copper was achieved when N-nitroso-N-phenylhydroxylamine (cupferron) chelation–extraction was employed for the separation of tellurium from copper matrix. Cupferron chelation–extraction was performed in phosphate buffer (a mixture of 0.2 mol l−1 sodium phosphate and 0.1 mol l−1 citric acid). Lanthanum hydroxide coprecipitation at pH 10.0±0.5 was effective for bismuth and selenium. Standard reference materials of nickel-based alloys and pure copper were analyzed using the proposed methods. The linear range for the calibration curves were 0.30–15 and 0.20–10 ng ml−1 for BiH3 and H2Se, respectively, with a correlation coefficient of 0.9995. For H2Te, the linear range for the calibration curves was 0.50–12 ng ml−1 with the correlation coefficient of 0.9994. Good agreement was obtained between experimental values and certified values. Satisfactory recovery ranged from 91±1 to 106±2% was obtained from five replicate determinations.
Keywords: Bismuth; Selenium; Tellurium; Nickel-based alloy; Pure copper; Flow-injection; Hydride generation atomic absorption spectrometry;