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Analytica Chimica Acta (v.638, #1)

Editorial Board (pp. iii).

A 21st century technique for food control: Electronic noses by Miguel Peris; Laura Escuder-Gilabert (pp. 1-15).

This work examines the main features of modern electronic noses (e-noses) and their most important applications in food control in this new century. The three components of an electronic nose (sample handling system, detection system, and data processing system) are described. Special attention is devoted to the promising mass spectrometry based e-noses, due to their advantages over the more classical gas sensors. Applications described include process monitoring, shelf-life investigation, freshness evaluation, authenticity assessment, as well as other general aspects of the utilization of electronic noses in food control. Finally, some interesting remarks concerning the strengths and weaknesses of electronic noses in food control are also mentioned.

Keywords: Abbreviations; 4EP; 4-ethylphenol; 4EG; 4-ethylguaiacol; ANN; artificial neural network; APC; aerobic plate count; API; atomic pressure ionization; BAW; bulk acoustic wave; BP-ANN; back-propagation artificial neural network; BP; backpropagation; CA; cluster analysis; CART; classification and regression tree; CP; conducting polymer; CP-ANN; counterpropagation artificial neural network; DFA; discriminant factor analysis; DHS; dynamic headspace; DOE; design of experiments; e-nose; electronic nose; EC; electrochemical sensor; FCM; fuzzy C means; FDA; factorial discriminant analysis; FSGDA; forward step-wise general discriminant analysis; GA; genetic algorithm; GC; gas chromatography; GC–MS; gas chromatography–mass spectrometry; HS; headspace; HS-MS; head-space mass spectrometry; IMS; ion mobility spectrometry; INDEX; inside-needle dynamic extraction; k; -NN; k; -nearest neighbors; KOSM; Kohonen self-organizing map; LDA; linear discriminant analysis; LVQ-NN; learning vector quantisation neural network; MDA; multiple discriminant analysis; MIMS; membrane introduction mass spectrometry; MLP; multilayer percepton; MLR; multiple linear regression; MOS; metal oxide semiconductors; MOSFET; metal oxide semiconductor field effect transistor; MS; mass spectrometry; MSE-nose; mass spectrometry based electronic nose; p-AV; anisidine value; P&T; purge and trap; PARAFAC; parallel factor analysis; PCA; principal component analysis; PCR; principal component regression; PLS; partial least squares; PLS-DA; partial least square-discriminant analysis; PNN; probabilistic neural network; PR; pattern recognition; PTR; proton transfer reaction; PV; peroxide value; QDA; quadratic discriminant analysis; QLSR; quadratic least squares regression; QMB or QCM; quartz microbalances; REP-PCR; repetitive extragenic palindromic polymerase chain reaction; SAW; surface acoustic wave; SBSE; stir bar sorptive extraction; SHS; static headspace; SIMCA; soft independent modelling of class analogy; SLDA; stepwise linear discriminant analysis; SOM; self-organizing map; SPME; solid-phase microextraction; SPR; surface plasmon resonance; SVM; support vector machine; TBARS; thiobarbituric acid reactive substances; TDNN; time-delay neural networks; TSM; thickness shear mode; VOCs; volatile organic compounds; WPTER; wavelet packet transform for efficient pattern recognitionElectronic noses; Food analysis; Gas sensors; Mass spectrometry

Detecting the quality of glycerol monolaurate: A method for using Fourier transform infrared spectroscopy with wavelet transform and modified uninformative variable elimination by Xiaojing Chen; Di Wu; Yong He; Shou Liu (pp. 16-22).

Glycerol monolaurate (GML) products contain many impurities, such as lauric acid and glucerol. The GML content is an important quality indicator for GML production. A hybrid variable selection algorithm, which is a combination of wavelet transform (WT) technology and modified uninformative variable eliminate (MUVE) method, was proposed to extract useful information from Fourier transform infrared (FT-IR) transmission spectroscopy for the determination of GML content. FT-IR spectra data were compressed by WT first; the irrelevant variables in the compressed wavelet coefficients were eliminated by MUVE. In the MUVE process, simulated annealing (SA) algorithm was employed to search the optimal cutoff threshold. After the WT-MUVE process, variables for the calibration model were reduced from 7366 to 163. Finally, the retained variables were employed as inputs of partial least squares (PLS) model to build the calibration model. For the prediction set, the correlation coefficient ( r) of 0.9910 and root mean square error of prediction (RMSEP) of 4.8617 were obtained. The prediction result was better than the PLS model with full-spectra data. It was indicated that proposed WT-MUVE method could not only make the prediction more accurate, but also make the calibration model more parsimonious. Furthermore, the reconstructed spectra represented the projection of the selected wavelet coefficients into the original domain, affording the chemical interpretation of the predicted results. It is concluded that the FT-IR transmission spectroscopy technique with the proposed method is promising for the fast detection of GML content.

Keywords: Fourier transform infrared spectroscopy; Glycerol monolaurate; Partial least squares; Wavelet transform; Uninformative information elimination; Simulated annealing; Nondestructive measurement

Mesoporous silica-based electrochemical sensor for sensitive determination of environmental hormone bisphenol A by Fengran Wang; Jinquan Yang; Kangbing Wu (pp. 23-28).

Bisphenol A (BPA) is an emerging contaminant with severe toxic effects such as disrupting endocrine system or causing cancer, therefore, developing sensitive and selective sensor for BPA is very important and interesting. Herein, MCM-41, a kind of mesoporous silica, was synthesized and then used to prepare an electrochemical sensor for BPA. For better comparison, carbon nanotubes, activated carbon, silica gel and graphite were also employed to prepare electrochemical sensor for BPA. The electrochemical behaviors of BPA at different electrochemical sensors were investigated. Compared with other sensors, the MCM-41 sensor greatly enhances the response signal of BPA due to the large active surface area and high accumulation efficiency. The effects of pH value, accumulation time and sensor composition were examined. The linear range is from 2.2×10⁻⁷ to 8.8×10⁻⁶molL⁻¹, and the limit of detection is evaluated to be 3.8×10⁻⁸molL⁻¹. Finally, the MCM-41 sensor was successfully employed to determine BPA in water samples.

Keywords: Electrochemical sensor; Bisphenol A (BPA); Determination; Mesoporous silica; Modified electrode

Determination of organochlorine pesticides in complex matrices by single-drop microextraction coupled to gas chromatography–mass spectrometry by Carol Cortada; Lorena Vidal; Sergio Tejada; Alicia Romo; Antonio Canals (pp. 29-35).

A rapid and simple single-drop microextraction method (SDME) has been used to preconcentrate eighteen organochlorine pesticides (OCPs) from water samples with a complex matrix. Exposing two microlitre toluene drop to an aqueous sample contaminated with OCPs proved an excellent preconcentration method prior to analysis by gas chromatography–mass spectrometry (GC–MS). A Plackett-Burman design was used for screening and a central composite design for optimizing the significant variables in order to evaluate several possibly influential and/or interacting factors. The studied variables were drop volume, aqueous sample volume, agitation speed, ionic strength and extraction time. The optimum experimental conditions of the proposed SDME method were: 2μL toluene microdrop exposed for 37min to 10mL of the aqueous sample containing 0% w/v NaCl and stirred at 380rpm.The calculated calibration curves gave high-level linearity for all target analytes with correlation coefficients ranging between 0.9991 and 0.9999. The repeatability of the proposed method, expressed as relative standard deviation, varied between 5.9 and 9.9% ( n=8). The detection limits were in the range of 0.022–0.101μgL⁻¹ using GC–MS with selective ion monitoring. The LOD values obtained are able to detect these OCPs in aqueous matrices as required by EPA Method 625. Analysis of spiked effluent wastewater samples revealed that the matrix had no effect on extraction for eleven of the analytes but exerted notable effect for the other analytes.

Keywords: Organochlorine pesticides; Single-drop microextraction; Experimental design; Complex matrix; Sample preparation

Sensitive determination of salicylate and benzophenone type UV filters in water samples using solid-phase microextraction, derivatization and gas chromatography tandem mass spectrometry by N. Negreira; I. Rodríguez; M. Ramil; E. Rubí; R. Cela (pp. 36-44).

A sensitive procedure for the determination of three UV filters: ethylhexyl salicylate (EHS), 3,3,5-trimethylcyclohexyl salicylate (Homosalate, HMS), 2-hydroxy-4-methoxybenzophenone (BP-3) and two related hydroxylated benzophenones (2,4-dihydroxybenzophenone, BP-1 and 2,2′-dihydroxy-4-methoxybenzophenone, BP-8) in water samples is presented. Analytes were first concentrated on the coating of a solid-phase microextraction (SPME) fibre, on-fibre silylated and then determined using gas chromatography combined with tandem mass spectrometry (GC–MS/MS). Factors affecting the performance of extraction and derivatization steps are thoroughly evaluated and their effects on the yield of the sample preparation discussed. Under final working conditions, a PDMS-DVB coated SPME fibre was exposed directly to 10mL of water, adjusted at pH 3, for 30min. After that, the fibre was placed in the headspace (HS) of a 1.5mL vial containing 20μL of N-methyl-N-(trimethylsilyl)-trifluoroacetamide (MSTFA). On-fibre silylation of hydroxyl groups contained in the structure of target compounds was performed at 45°C for 10min. The whole sample preparation process was completed in 40min, providing limits of quantification from 0.5 to 10ngL⁻¹ and acceptable precision (RSDs under 13%) for samples spiked at different concentrations. All compounds could be accurately determined in river and treated wastewater (relative recoveries from 89 to 115%) using standards in ultrapure water, whereas standard addition is recommended to quantify their levels in untreated wastewater. Analysis of wastewater revealed the systematic presence of BP-3 and BP-1 in raw samples with maximum concentrations close to 500 and 250ngL⁻¹, respectively.

Keywords: UV filters; Water samples; Solid-phase microextraction; Derivatization; Gas chromatography

Simple hollow fiber renewal liquid membrane extraction method for pre-concentration of Cd(II) in environmental samples and detection by Flame Atomic Absorption Spectrometry by Jeferson Schneider Carletto; Raquel Medeiros Luciano; Gizelle Cristina Bedendo; Eduardo Carasek (pp. 45-50).

A hollow fiber renewal liquid membrane (HFRLM) extraction method to determine cadmium (II) in water samples using Flame Atomic Absorption Spectrometry (FAAS) was developed. Ammonium O, O-diethyl dithiophosphate (DDTP) was used to complex cadmium (II) in an acid medium to obtain a neutral hydrophobic complex (ML₂). The organic solvent introduced to the sample extracts this complex from the aqueous solution and carries it over the poly(dimethylsiloxane) (PDMS) membrane, that had their walls previously filled with the same organic solvent. The organic solvent is solubilized inside the PDMS membrane, leading to a homogeneous phase. The complex strips the lumen of the membrane where, at higher pH, the complex Cd–DDTP is broken down and cadmium (II) is released into the stripping phase. EDTA was used to complex the cadmium (II), helping to trap the analyte in the stripping phase. A multivariate procedure was used to optimize the studied variables. The optimized variables were: sample (donor phase) pH 3.25, DDTP concentration 0.05% (m/v), stripping (acceptor phase) pH 8.75, EDTA concentration 1.5×10⁻²molL⁻¹, extraction temperature 40°C, extraction time 40min, a solvent mixture N-butyl acetate and hexane (60/40%, v/v) with a volume of 100μL, and addition of ammonium sulfate to saturate the sample. The sample volume used was 20mL and the stripping volume was 165μL. The analyte enrichment factor was 120, limit of detection (LOD) 1.3μgL⁻¹, relative standard deviation (RSD) 5.5% and the working linear range 2–30μgL⁻¹.

Keywords: Hollow fiber renewal liquid membrane; Cadmium; Flame Atomic Absorption Spectrometry; O; ,; O; -diethyl dithiophosphate; Poly(dimethylsiloxane) membrane

Optimizing the performance of tin dioxide microspheres for phosphopeptide enrichment by Alexander Leitner; Martin Sturm; Jan-Henrik Smått; Mikael Järn; Mika Lindén; Karl Mechtler; Wolfgang Lindner (pp. 51-57).

Phosphopeptide enrichment based on metal oxide affinity chromatography is one of the most powerful tools for studying protein phosphorylation on a large scale. To complement existing metal oxide sorbents, we have recently introduced tin dioxide as a promising alternative. The preparation of SnO₂ microspheres by the nanocasting technique, using silica of different morphology as a template, offers a strategy to prepare materials that vary in their particle size and their porosity. Here, we demonstrate how such stannia materials can be successfully generated and their properties fine-tuned in order to obtain an optimized phosphopeptide enrichment material. We combined data from liquid chromatography–mass spectrometry experiments and physicochemical characterization, including nitrogen physisorption and energy-dispersive X-ray spectroscopy (EDX), to explain the influence of the various experimental parameters.

Keywords: Phosphorylation; Phosphopeptide enrichment; Metal oxide affinity chromatography; Tin dioxide; Mass spectrometry; Nanocasting

Aminorex and rexamino as metabolites of levamisole in the horse by E.N.M. Ho; D.K.K. Leung; G.N.W. Leung; T.S.M. Wan; A.S.Y. Wong; C.H.F. Wong; L.R. Soma; J.A. Rudy; C. Uboh; R. Sams (pp. 58-68).

Administration studies of levamisole in horses were carried out using two different levamisole preparations, namely, levamisole hydrochloride oral bolus and levamisole phosphate injectable solution. These preparations were analysed in detail for the presence of aminorex-like impurities. Both levamisole preparations were found to contain 1-(2-mercaptoethyl)-4-phenyl-2-imidazolidinone (I) and 4-phenyl-2-imidazolidinone (II) as degradation impurities, but neither aminorex nor rexamino was detected in these preparations. After the administration of these preparations to horses, aminorex, rexamino, in addition to levamisole and compound II, were detected in post-administration urine and plasma samples, among which compound II was found to have the longest detection time. Administration study of compound II was then performed on another horse to investigate whether it could be a metabolic precursor of aminorex and/or rexamino. However, no aminorex and rexamino was detected in the post-administration samples, suggesting that compound II was not a metabolic precursor of aminorex or rexamino. A metabolite (III) of compound II, tentatively identified to be a hydrolysis product of compound II, was observed instead.It has been established unequivocally that the normal use of levamisole products in horses can lead to the presence of aminorex, rexamino and 4-phenyl-2-imidazolidinone (II) in their urine and blood samples. As compound II has the longest detection time, the detection of aminorex (and in some cases rexamino) in some of the official samples from racehorses can be ascribed to the use of levamisole products as long as compound II is also present as a marker. These findings should be of direct relevance to the investigation of some of the cases of aminorex detection in official doping control samples from racehorses.

Keywords: Levamisole; Aminorex; Rexamino; Metabolism; Horse

Solid substrate-room temperature phosphorimetry for the determination of residual clenbuterol hydrochloride based on the catalysis of sodium periodate oxidizing eosine Y by Jiaming Liu; Liqing Zeng; Zhiming Li; Fei Gao; Xiaomei Huang; Feiming Li; Huiqing Lin (pp. 69-74).

Clenbuterol hydrochloride (CLB) could catalyze NaIO₄ oxidation of eosine Y (R), which caused the room temperature phosphorescence (RTP) signal of R to quench sharply. The Δ I_P (= I_P2− I_P1, I_P2 was RTP intensities of reagent blank and I_P1 was RTP intensities of test solution) of the system was directly proportional to the content of CLB. According to that academic thought, a new solid substrate-room temperature phosphorimetry (SS-RTP) for the determination of trace CLB has been established. This method has high sensitivity (detection limit (LD): 0.021zgspot⁻¹, corresponding concentration: 5.2×10⁻²⁰gmL⁻¹) and good selectivity (Er=±5%, interfering species were of no interference). It has been applied to the determination of residual CLB in the practical samples. The results were verified using HPLC and GC/MS methods. The reaction mechanism of catalytic SS-RTP for the determination of residual CLB was also discussed.

Keywords: Clenbuterol hydrochloride; Eosine Y; Catalytic solid substrate-room temperature phosphorimetry; Residual detection technique

One step purification of the grape vacuolar invertase by Sandrine Jégou; Alexandra Conreux; Sandra Villaume; Agnès Hovasse; Christine Schaeffer; Clara Cilindre; Alain Van Dorsselaer; Philippe Jeandet (pp. 75-78).

Invertase is a major protein of grape juice and wine. Accordingly, in order to study the biochemical and structural characteristics of this protein and for a better understanding of its physico-chemical properties, large amounts of the pure protein are needed. A simple method for the purification of the grape vacuolar invertase in a preparative-scale is described in this work. The grape protein was isolated and purified from must by ultrafiltration and anion exchange chromatography. The identification and purity determination of the grape invertase fraction were assessed by SDS-PAGE, and were then confirmed using nanoLC-chip-MS/MS analysis. The laboratory fractionation procedure presented in this work generated large quantities of pure grape vacuolar invertase from must.

Keywords: Abbreviations; SDS-PAGE; sodium dodecyl sulfate polyacrylamide gel electrophoresis; LC; liquid chromatography; MS/MS; tandem mass spectrometry; NCBI; National Center for Biotechnology Information; EDTA; ethylenediaminetetraacetic acid; DTT; dithiothreitolGrape must; Protein; Invertase; Purification; Ion exchange chromatography; Mass spectrometry

Py-GC/MS, GC/MS and FTIR investigations on LATE Roman-Egyptian adhesives from opus sectile: New insights into ancient recipes and technologies by Erika Ribechini; Sibilla Orsini; Flora Silvano; Maria Perla Colombini (pp. 79-87).

An analytical protocol based on optical microscopy, Fourier transforms infrared spectroscopy (FTIR), analytical pyrolysis in the presence of hexamethyldisilazane followed by gas chromatographic/mass spectrometric analysis (Py-GC/MS) and gas chromatography/mass spectrometry after alkaline hydrolysis, solvent extraction and trimethylsilylation (GC/MS) was used in the chemical characterisation of the original adhesives used to fix monochrome and mosaic glass and stone plaques coming from the Late Roman archaeological site of Antinoopolis (Egypt).FTIR analysis demonstrated the presence of calcite fragments, and Py-GC/MS and GC/MS analyses provided detailed molecular compositions, highlighting the presence of a wide range of compound classes including diterpenoid acids, tricyclic abietanes with a high degree of aromatisation, mid- and long-chain monocarboxylic fatty acids, mono- and di-hydroxy acids, α,ω-dicaboxylic fatty acids, n-alkanols, and n-alkanes. Characteristic biomarkers and their distribution patterns indicated the presence of pine pitch in all the adhesives, which in some cases was admixed with beeswax and brassicaceae seed oil.The results provided new insights into the complex recipes used by artisans in ancient Egypt in the production of adhesives and in the sophisticated manufacture of opus sectile decorations.

Keywords: Pyrolysis-gas chromatography/mass spectrometry; Gas chromatography/mass spectrometry; Pine pitch; Beeswax; Brassica oil; Archaeological adhesives

Application of experimental design and radial basis function neural network to the separation and determination of active components in traditional Chinese medicines by capillary electrophoresis by Huitao Liu; Yingying Wen; Feng Luan; Yuan Gao (pp. 88-93).

Orthogonal design has been used to the optimization of separation and determination of two active components in traditional Chinese medicines by capillary electrophoresis. The concentration of phosphate, applied voltage, organic modifier content and buffer pH were selected as variable parameters. Their different effects on peak resolution were studied by the experimental design method. Optimized separation conditions were obtained and successfully applied to the separation and determination of aconitine and hypaconitine in Aconitum medicinal herbs. Good separation was achieved within 7min using a buffer system composed of 20mmolL⁻¹ phosphate and 35% acetonitrile at pH 9.5. The applied voltage was 14kV and the detection was set at 235nm. In addition, a radial basis function neural network with a “4-18-1” structure was developed based on the experimental results of orthogonal design and uniform design, and was applied to the prediction of peak resolution of the two active components under the optimum separation conditions given by orthogonal design. The predicted results were in good agreement with the experimental values, indicating that radial basis function neural network is a potential way for the selection of separation conditions in capillary electrophoresis.

Keywords: Capillary electrophoresis; Experimental design; Radial basis function neural network; Aconitine; Hypaconitine

An enzyme-linked immunometric assay for cortisol based on idiotype–anti-idiotype reactions by Toshifumi Niwa; Takayuki Kobayashi; Pi Sun; Junichi Goto; Hiroyuki Oyama; Norihiro Kobayashi (pp. 94-100).

Cortisol levels in body fluids are useful for monitoring the function of the pituitary–adrenal axis. Here, we established an “enzyme-linked immunometric assay” (a noncompetitive-type ELISA) for cortisol based on idiotype–anti-idiotype reactions. Six different anti-idiotype monoclonal antibodies that recognized the variable regions of a newly established anti-cortisol antibody were generated using hybridoma technology; these were two β-type and four α-type anti-idiotype antibodies, recognizing the paratope and framework regions, respectively. An immunometric assay was established using a combination of a selected α-type and a selected β-type antibody. The analyte (cortisol) was captured by an excess amount of anti-cortisol antibody immobilized on microplates, and the unoccupied paratope was saturated with the β-type antibody. Hapten-occupied anti-cortisol antibody, with less steric hindrance, was then selectively bound by the α-type antibody, labeled with biotin. The amount of biotin residue on the microplates was colorimetrically monitored using a peroxidase-labeled streptavidin. This assay had an approximately threefold higher sensitivity (detection limit: 90pg=248fmol cortisol) than a competitive ELISA using the same anti-cortisol antibody, as well as a practical specificity for providing reasonable determination of normal urinary cortisol levels.

Keywords: Noncompetitive assay; Enzyme-linked immunosorbent assay; Anti-idiotype antibody; Monoclonal antibody; Hapten; Cortisol

Microwave-assisted total digestion of sulphide ores for multi-element analysis by M. Al-Harahsheh; S. Kingman; C. Somerfield; F. Ababneh (pp. 101-105).

A new two-stage microwave-assisted digestion procedure using concentrated HNO₃, HCl, HF and H₃BO₃ has been developed for the chemical analysis of major and trace elements in sulphide ore samples prior to inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis. In the first stage 0.2g of the certified reference material (CRM) sample was digested with a combination of acids (HNO₃, HCl, and HF) in a closed Teflon vessel and heated in the microwave to 200°C for 30min. After cooling, H₃BO₃ was added and the vessel was reheated to 170°C for 15min. The precision of the method was checked by comparing the results against six certified reference materials. The analytical results obtained were in good agreement with the certified values, in most cases the recoveries were in the range 95–105%. Based on at least 17 replicates of sample preparation and analysis, the precision of the method was found to be ≤5%.

Keywords: Microwave digestion; Sulphide ores; Total digestion; Inductively coupled plasma atomic emission spectroscopy

Identification of potential gene expression biomarkers for the surveillance of anabolic agents in bovine blood cells by Irmgard Riedmaier; Ales Tichopad; Martina Reiter; Michael W. Pfaffl; Heinrich H.D. Meyer (pp. 106-113).

In the EU, the use of anabolic steroids in food producing animals has been forbidden since 1988. The routine methods used in practice are based on the detection of hormonal residues. To overcome these routine methods, growth-promoting agents are sometimes administered at concentrations below the detection limit and new anabolic substances are designed. Therefore, new monitoring systems are needed to overcome the misuse of anabolic agents in meat production.In this study, a new monitoring system was applied: the quantification of mRNA gene expression changes by quantitative real time reverse transcription polymerase chain reaction (qRT-PCR). Blood was selected as ideal tissue for biomarker screening. From the literature, it is known that steroid hormones affect mRNA gene expression of the different blood cells, which can easily be taken from the living animal.In an animal trial, 18 Nguni heifers were separated to two groups of nine animals. One group served as untreated control and the other group was treated with a combination of trenbolone acetate plus estradiol for 39 days in order to allow the detection of the effect on mRNA expression in blood at three time points. Candidate genes used for developing a biomarker pattern were chosen by screening the actual literature for anabolic effects on blood cells.It could be demonstrated that the combination of trenbolone acetate plus estradiol significantly influences mRNA expression of the steroid receptors (ER-α and GR-α), the apotosis regulator Fas, the proinflammatory interleukins IL-1α, IL-1β and IL-6 and of MHCII, CK, MTPN, RBM5 and Actin-β. Advanced statistical analysis by Principal Components Analysis (PCA) indicated that these genes represent potential biomarkers for this hormone combination in whole blood.

Keywords: Anabolic agents; Trenbolone acetate; Estradiol; Biomarker; Gene expression; Quantitative real time reverse transcription polymerase chain reaction (qRT-PCR); Principal components analysis

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Analytica Chimica Acta (v.638, #1)