Analytica Chimica Acta (v.615, #1)

Contents (v-vi).

The aim of this manuscript is to provide a condensed overview of the contribution of certain relatively new semiconductor substrates in the development of chemical and biochemical field effect transistors. The silicon era is initially reviewed providing the background onto which the deployment of the new semiconductor materials for the development of bio-chem-FETs is based on. Subsequently emphasis is given to the selective interaction of novel semiconductor surfaces, including doped conductive diamond, gallium nitride, and indium nitride, with the analyte, and how this interaction can be properly transduced using semiconductor technology. The main advantages and drawbacks of these materials, as well as their future prospects for their applications in the sensor area are also described.
Keywords: Chemical sensor; Biosensor; Semiconductor; Gallium nitride; Indium nitride; Conductive diamond; Transduction; Surface potential;

Near infrared (NIR) spectroscopy based on effective wavelengths (EWs) and chemometrics was proposed to discriminate the varieties of fruit vinegars including aloe, apple, lemon and peach vinegars. One hundred eighty samples (45 for each variety) were selected randomly for the calibration set, and 60 samples (15 for each variety) for the validation set, whereas 24 samples (6 for each variety) for the independent set. Partial least squares discriminant analysis (PLS-DA) and least squares-support vector machine (LS-SVM) were implemented for calibration models. Different input data matrices of LS-SVM were determined by latent variables (LVs) selected by explained variance, and EWs selected by x-loading weights, regression coefficients, modeling power and independent component analysis (ICA). Then the LS-SVM models were developed with a grid search technique and RBF kernel function. All LS-SVM models outperformed PLS-DA model, and the optimal LS-SVM model was achieved with EWs (4021, 4058, 4264, 4400, 4853, 5070 and 5273 cm−1) selected by regression coefficients. The determination coefficient (R 2), RMSEP and total recognition ratio with cutoff value ±0.1 in validation set were 1.000, 0.025 and 100%, respectively. The overall results indicted that the regression coefficients was an effective way for the selection of effective wavelengths. NIR spectroscopy combined with LS-SVM models had the capability to discriminate the varieties of fruit vinegars with high accuracy.
Keywords: Near infrared spectroscopy; Fruit vinegars; Discrimination; Effective wavelengths; Partial least squares discriminant analysis; Least squares-support vector machine;

More than one multi-informative analytical technique is often applied when describing the condition of a set of samples. Often a part of the information found in these data blocks is redundant and can be extracted from more blocks. This study puts forward a method (multiblock variance partitioning—MVP) to compare the information/variation in different data blocks using simple quantitative measures. These measures are the unique part of the variation only found in one data block and the common part that can be found in more data blocks. These different parts are found using PLS models between predictor blocks and a common response. MVP provides a different view on the information in different blocks than normal multiblock analysis. It will be shown that this has many applications in very diverse fields such as process control, assessor performance in sensory analysis, efficiency of preprocessing methods and as complementary information to an interval PLS analysis. Here the ideas of the MVP approach are presented in detail using a study of red wines from different regions measured with GC–MS and FT-IR instruments providing different kinds of data representations.
Keywords: Multiblock; Partial least squares; Unique variation;

Carboxylated multiwalled carbon nanotubes (MWCNT-COOH) were used to modify the working electrode surface of different screen-printed electrodes. The effect of this modification on the electrodic characteristics (double layer capacitance, electroactive area and heterogeneous rate constants for the electron transfer) was evaluated and optimized for the cyclic voltammetric determination of p-aminophenol. The enzymatic hydrolysis of p-aminophenylphosphate was employed for the quantification of alkaline phosphatase, one of the most important label enzymes in immunoassays. Finally, ELISA assays were carried out to quantify pneumolysin using this enzymatic system. Results obtained indicated that low superficial densities of MWCNT-COOH (0.03–0.06 μg mm−2) yielded the same electrodic improvements but with better analytical properties.
Keywords: Alkaline phosphatase; Screen-printed electrode; p-Aminophenol; Enzyme-Linked ImmunoSorbent Assay; Carbon nanotube;

The study of a new type of working electrode – the renovated silver ring electrode (RSRE) – for lead ions detection via differential pulse anodic stripping voltammetry (DP ASV) without removal of oxygen is reported. The only four constituents of the RSRE: a specially constructed silver ring electrode, a silver sheet used as silver counter/quasi-reference electrode and a silicon O-ring, are fastened together in a polypropylene body. The renovation of this electrode is carried out through mechanical removal of solid contaminants and electrochemical activation in the electrolyte which fills the RSRE body. Excellent repeatability and reproducibility – also in organic samples solutions – were reached in a period of a few weeks through the renovation of the electrode surface before each measurement. The reduction and stripping of lead on silver electrode under the DP ASV conditions are underpotential deposition/dissolution phenomena. The RSRE is used for the determination of Pb ions in concentrations ranging from 1 × 10−9 to 1 × 10−7  M. The repeatability of DP ASV runs in synthetic solutions covering the entire concentration range is better than 2%. Obtained calibration curves are represented by a correlation coefficient of at least 0.999. The detection limit (LOD) for the time of electrodeposition equal to 60 s is 0.2 × 10−9  M. LOD for Pb2+ detection at the RSRE is similar to this reported for a rotating silver electrode in subtractive anodic stripping voltammetry (E. Kirowa-Eisner, et al., Anal. Chim. Acta, 385 (1999) 325). The analysis of Pb2+ in synthetic solutions with and without surfactants, certified reference materials and natural water samples have been performed.
Keywords: Silver electrode; Underpotential deposition; Stripping voltammetry; Mercury-free electroanalysis; Trace analysis; Lead;

Microwave-assisted extraction using 1 M KOH/methanol (alkaline-MAE) in combination with solid-phase extraction treatment was developed and applied to polycyclic aromatic hydrocarbons (PAHs) in a sediment sample. Although various conditions were examined (100 or 150 °C for 10 or 30 min), comparable concentrations of PAHs to those obtained by conventional extraction with 1 M KOH/methanol at 70 °C for 4 h were obtained, even at 100 °C for 10 min. The concentrations obtained by using MeOH at 150 °C for 30 min without KOH were lower (by 1.3–37%) than those obtained by alkaline-MAE at 150 °C for 30 min. Since the developed technique can introduce higher concentration of benzo[ghi]perylene relative to those using pressurized liquid extraction (toluene, 150 °C, 15 MPa, 10 min, two cycles), the developed alkaline-MAE is a effective technique.
Keywords: Polycyclic aromatic hydrocarbons (PAHs); Microwave-assisted extraction (MAE); Alkaline extraction; Isotope dilution mass spectrometry (IDMS); Sediment;

In this study, molecularly imprinted poly (methacrylamide-co-methacrylic acid) composite membranes with different ratio of methacrylamide (MAM) versus methacrylic acid (MAA) were prepared via UV initiated photo-copolymerization on the commercial filter paper. Curcumin was chosen as the template molecule. Infra-red (IR) spectroscopy was used to study the binding mechanism between the imprinted sites and the templates. The morphology of the resultant membranes was visualized by scanning electron microscopy (SEM). Static equilibrium binding and recognition properties of the imprinted composite membranes to curcumin (cur-I) and its analogues demethoxycurcumin (cur-II) or bisdemethoxycurcumin (cur-III) were tested. The results showed that curcumin-imprinted membranes had the best recognition ability to curcumin compared to its analogues. From the results, the biggest selectivity factor of αcur-I/cur-II and αcur-I/cur-III were 1.50 and 5.94, and they were obtained from the composite membranes in which MAM/MAA were 1:4 and 0:1, respectively. The results of this study implied that the molecularly imprinted composite membranes could be used as separation membranes for curcumin enrichment.
Keywords: Molecular imprinting; Photo-copolymerization; Composite membrane; Selective separation; Curcumins;

In-situ detection of drugs-of-abuse on clothing using confocal Raman microscopy by Esam M.A. Ali; Howell G.M. Edwards; Michael D. Hargreaves; Ian J. Scowen (63-72).
This study describes the application of confocal Raman microscopy to the detection and identification of drugs-of-abuse in situ on undyed natural synthetic fibres, and coloured textile specimens. Raman spectra were obtained from drug particles trapped between the fibres of the specimens. Pure samples of cocaine hydrochloride and N-methyl-3,4-methylenedioxy-amphetamine HCl (MDMA-HCl) were used in this study. Raman spectra were collected from drug particles of an average size in the range 5–15 μm. Despite the presence of spectral bands arising from the natural and synthetic polymer and dyed textiles, the drugs could be identified by their characteristic Raman bands. If necessary, interfering bands could be successfully removed by spectral subtraction. Furthermore, Raman spectra were recorded from drug particles trapped between the fibres of highly fluorescent specimens. Interference from the fibres, including background fluorescence, was overcome by careful focusing of the confocal beam and the resulting spectra allow ready differentiation from interference from the fibres substrate bands. Spectra of several drugs-of-abuse on dyed and undyed clothing substrates were readily obtained within 3 min with little or no sample preparation and with no alteration of the evidential material.
Keywords: Cocaine hydrochloride; N-methyl-3,4-methylenedioxy-amphetamine hydrochloride; Confocal Raman microscopy; Textiles; Drug discrimination; Forensic;

Development of a conductometric phosphate biosensor based on tri-layer maltose phosphorylase composite films by Zhiqiang Zhang; Nicole Jaffrezic-Renault; François Bessueille; Didier Leonard; Siqing Xia; Xuejiang Wang; Ling Chen; Jianfu Zhao (73-79).
A conductometric biosensor for phosphate detection was developed using maltose phosphorylase (MP) from recombinant Escherichia coli immobilized on a planar interdigitated electrode by cross-linking with saturated glutaraldehyde (GA) vapour in the presence of bovine serum albumin (BSA). The process parameters for the fabrication of the mono-enzymatic sensor and various experimental variables such as the enzyme loading, time of immobilization in saturated GA vapour, working buffer solution and temperature were investigated with regard to their influence on sensitivity, detection limit, dynamic range, operational and storage stability. The biosensor can work well at the temperature between 20 °C and 50 °C, and reach 90% of steady-state conductance in about 10 s. The sensor has two linear ranges, one is from 1.0 μM to 20 μM phosphate with a detection limit of 1.0 μM, and the other is between 20 μM and 400 μM phosphate. When stored in citrate buffer (0.1 M, pH 6.0) at 4 °C, the biosensor showed good stability over two months. No obvious interference from other anionic species like SO4 2−, Cl, NO3 , NO2 and HCO3 was detected. The biosensor is suitable for use in real water samples.
Keywords: Conductometric biosensor; Phosphate; Maltose phosphorylase; Monoenzyme; Multilayer;

A cell-microelectronic sensing technique for profiling cytotoxicity of chemicals by Jessica M. Boyd; Li Huang; Li Xie; Birget Moe; Stephan Gabos; Xing-Fang Li (80-87).
A cell-microelectronic sensing technique is developed for profiling chemical cytotoxicity and is used to study different cytotoxic effects of the same class chemicals using nitrosamines as examples. This technique uses three human cell lines (T24 bladder, HepG2 liver, and A549 lung carcinoma cells) and Chinese hamster ovary (CHO-K1) cells in parallel as the living components of the sensors of a real-time cell electronic sensing (RT-CES) method for dynamic monitoring of chemical toxicity. The RT-CES technique measures changes in the impedance of individual microelectronic wells that is correlated linearly with changes in cell numbers during t log phase of cell growth, thus allowing determination of cytotoxicity. Four nitrosamines, N-nitrosodimethylamine (NDMA), N-nitrosodiphenylamine (NDPhA), N-nitrosopiperidine (NPip), and N-nitrosopyrrolidine (NPyr), were examined and unique cytotoxicity profiles were detected for each nitrosamine. In vitro cytotoxicity values (IC50) for NDPhA (ranging from 0.6 to 1.9 mM) were significantly lower than the IC50 values for the well-known carcinogen NDMA (15–95 mM) in all four cell lines. T24 cells were the most sensitive to nitrosamine exposure among the four cell lines tested (T24 > CHO > A549 > HepG2), suggesting that T24 may serve as a new sensitive model for cytotoxicity screening. Cell staining results confirmed that administration of the IC50 concentration from the RT-CES experiments inhibited cell growth by 50% compared to the controls, indicating that the RT-CES method provides reliable measures of IC50. Staining and cell-cycle analysis confirmed that NDPhA caused cell-cycle arrest at the G0/G1 phase, whereas NDMA did not disrupt the cell cycle but induced cell death, thus explaining the different cytotoxicity profiles detected by the RT-CES method. The parallel cytotoxicity profiling of nitrosamines on the four cell lines by the RT-CES method led to the discovery of the unique cytotoxicity of NDPhA causing cell-cycle arrest. This study demonstrates a new approach to comprehensive testing of chemical toxicity.
Keywords: Cell electronic sensing; Nitrosamines; Chemical cytotoxicity; Environmental monitoring;

Three different quantitative methods, which rely on base-mediated reactions for the purity assessment of the hydrolytically unstable activated ester, mPEG-SC (1) are discussed. In a spectrophotometric assay, controlled base-catalyzed hydrolysis of mPEG-SC (1) affords N-hydroxysuccinimide and its concentration can be determined by UV analysis. Reaction of mPEG-SC (1) with benzylamine and a non-aqueous back titration of the remaining benzylamine can also be used for purity determination of mPEG-SC (1). HPLC analysis of derivatized forms of mPEG-SC (1) affords a potential specific assay for these polymers. The relative attributes and shortcomings of these methods are elaborated. Although the titration assay is intermediate in specificity, the greater precision of the method makes it the preferred method at this stage of development of an HPLC–ELSD or HPLC–UV assay method. The percent relative standard deviation (%R.S.D.) of the titration method was 2.9% as opposed to 8.8% for the HPLC assay. The accuracy of the titration method was shown to be 101 ± 4.0% and was sufficient to justify a blending operation according to FDA cGMP guidelines.
Keywords: Monomethoxypoly(ethylene glycol)succinimido carbonate; Titration; Polymers; End-group characterization;

A simple, rapid and efficient method, dispersive liquid–liquid microextraction (DLLME), has been developed for the extraction and preconcentration of polybrominated diphenyl ethers (PBDEs) in water samples. The factors influencing microextraction efficiencies, such as the kind and volume of extraction and dispersive solvent, the extraction time and the salt effect, were optimized. Under the optimum conditions (sample volume: 5 mL; extraction solvent: tetrachloroethane, 20.0 μL; dispersive solvent: acetonitrile, 1.00 mL; extraction time: below 5 s and without salt addition), the enrichment factors and extraction recoveries were high and ranged from 268 to 305 and 87.0 to 119.1%, respectively. Linearity was observed in the range 0.05–50 ng mL−1 for BDE-28 and BDE-99, and 0.1–100 ng mL−1 for BDE-47 and BDE-209, respectively. Coefficients of correlation (r 2) ranged from 0.9995 to 0.9999. The repeatability study was carried out by extracting the spiked water samples at concentration levels of 50 ng mL−1 for BDE-28 and BDE-99, and 100 ng mL−1 for BDE-47 and BDE-209, respectively. The relative standard deviations (R.S.D.s) varied between 3.8 and 6.3% (n  = 5). The limits of detection (LODs), based on signal-to-noise ratio (S/N) of 3, ranged from 12.4 to 55.6 pg mL−1 (the wavelength of detector at 226 nm). The relative recoveries of PBDEs from tap, lake water and landfill leachate samples at spiking levels of 5, 10 and 50 ng mL−1 were in the range of 89.7–107.6%, 114.3–119.1% and 87.0–90.9%, respectively. As a result, this method can be successfully applied for the determination of PBDEs in landfill leachate and environmental water samples.
Keywords: Dispersive liquid–liquid microextraction; Polybrominated diphenyl ethers; Reversed phase-high performance liquid chromatography; Landfill leachate; Water sample;