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Analytica Chimica Acta (v.671, #1-2)
Murillo's paintings revealed by spectroscopic techniques and dedicated laboratory-made micro X-ray diffraction by A. Duran; M.B. Siguenza; M.L. Franquelo; M.C. Jimenez de Haro; A. Justo; J.L. Perez-Rodriguez (pp. 1-8).
This paper describes one of the first case studies using micro-diffraction laboratory-made systems to analyse painting cross-sections. Pigments, such as lead white, vermilion, red ochre, red lac, lapis lazuli, smalt, lead tin yellow type I, massicot, ivory black, lamp black and malachite, were detected in cross-sections prepared from six Bartolomé Esteban Murillo paintings by micro-Raman and micro-XRD combined with complementary techniques (optical microscopy, SEM-EDS, and FT-IR). The use of micro-XRD was necessary due to the poor results obtained with conventional XRD. In some cases, pigment identification was only possible by combining results from the different analytical techniques utilised in this study.
Keywords: Laboratory-made micro X-ray diffraction system; Micro-Raman spectroscopy; Cross-sections; Murillo's paintings
High performance liquid chromatography coupled to atomic fluorescence spectrometry for the speciation of the hydride and chemical vapour-forming elements As, Se, Sb and Hg: A critical review by Yu-Wei Chen; Nelson Belzile (pp. 9-26).
We present the most recent applications of high performance liquid chromatography (HPLC) hyphenated to hydride generation or chemical vapour generation and atomic fluorescence spectrometry (HG/CVG-AFS), for the determination and speciation of the selected hydride-forming elements arsenic (As), selenium (Se) and antimony (Sb) and the chemical vapour-forming metal Hg. The review focuses on sample preparation, post-column treatments and on the applications of this technique to various liquid and solid samples. This review also intends to discuss some limitations associated to HPLC-HG/CVG-AFS due to the necessity on post-column treatments, including the oxidation of organo-element compounds and the pre-reduction to a suitable valence. Nevertheless, the hyphenated technique HPLC-HG/CVG-AFS remains an efficient, sensitive and affordable approach to perform speciation of the four studied elements as shown by the variety of applications presented and discussed in this review.
Keywords: HPLC; AFS; Hydride generation; Chemical vapour generation; Elemental speciation; Arsenic; Selenium; Antimony; MercuryAbbreviations; AB; arsenobetaine; Ac; acetate; AC; arsenocholine; AFS; atomic fluorescence spectrometry; APDC; ammonium pyrolidine-1-yl-dithicarbamate; APM; atmospheric particulate matter; CCA; chromate-copper arsenate; CVG; chemical vapour generation; DBDTC; dibenzyldithiocarbamate; DAT; diammonium tartrate; DDTC; sodium diethyldithiocarbamate; DL; detection limit; DMA; dimethlylarsinic acid; DDAB; didocecyl-dimethyl-ammonium-bromide; DMPS; 2,3-Dimercapto-1-propane sulfonate; EDTA; ethylenediaminetetraacetic acid; EtHg; +; ethylmercury ion; GLS; gas–liquid separator; HHPN; hydraulic high pressure nebulizer; HG; hydride generation; HPLC; high performance liquid chromatography; KHP; potassium hydrogen phthalate; MeOH; methanol; MMA; monomethylarsonic acid; MMA(III); monomethylarsonous acid; MSPD; matrix solid-phase dispersion; MW; microwave; PCRD; photocatalysis reaction device; PhHg; +; phenylmercury ion; PICVG; photo-induced chemical vapour generation; RPPC; reversed-phase partition chromatography; Se-Cys; selenocysteine; Se-Cys; 2; selenocystine; Se-Cyt; selenocystamine; Se-Et; selenoethionine; Se-Met; selenomethionine; Se-Me-Se-Cys; selenium methylselenocysteine; SPDC; sodium pyrrolidinedithiocarbamate; SPDC; sodium pyrrolidinedithiocarbamate; TBAA; tetrabutyl-ammonium acetate; TBAH; tetrabutylammonium hydroxide; TEACl; tetraethylammonium chloride; TEAH; tetraethylammonium hydroxide; TFA; trifluoroacetic acid; TMAH; tetramethylammonium hydroxide; TMAO; trimethlyarsine oxide; TMA; +; tetramethylarsonium ion; TMSb; trimethylantimony; UPLC; Ultra Performance Liquid Chromatography; USN; ultrasonic nebulizer
Gasoline classification using near infrared (NIR) spectroscopy data: Comparison of multivariate techniques by Roman M. Balabin; Ravilya Z. Safieva; Ekaterina I. Lomakina (pp. 27-35).
Near infrared (NIR) spectroscopy is a non-destructive (vibrational spectroscopy based) measurement technique for many multicomponent chemical systems, including products of petroleum (crude oil) refining and petrochemicals, food products (tea, fruits, e.g., apples, milk, wine, spirits, meat, bread, cheese, etc.), pharmaceuticals (drugs, tablets, bioreactor monitoring, etc.), and combustion products. In this paper we have compared the abilities of nine different multivariate classification methods: linear discriminant analysis (LDA), quadratic discriminant analysis (QDA), regularized discriminant analysis (RDA), soft independent modeling of class analogy (SIMCA), partial least squares (PLS) classification, K-nearest neighbor (KNN), support vector machines (SVM), probabilistic neural network (PNN), and multilayer perceptron (ANN-MLP) – for gasoline classification. Three sets of near infrared (NIR) spectra (450, 415, and 345 spectra) were used for classification of gasolines into 3, 6, and 3 classes, respectively, according to their source (refinery or process) and type. The 14,000–8000cm−1 NIR spectral region was chosen. In all cases NIR spectroscopy was found to be effective for gasoline classification purposes, when compared with nuclear magnetic resonance (NMR) spectroscopy or gas chromatography (GC). KNN, SVM, and PNN techniques for classification were found to be among the most effective ones. Artificial neural network (ANN-MLP) approach based on principal component analysis (PCA), which was believed to be efficient, has shown much worse results. We hope that the results obtained in this study will help both further chemometric (multivariate data analysis) investigations and investigations in the sphere of applied vibrational (infrared/IR, near-IR, and Raman) spectroscopy of sophisticated multicomponent systems.
Keywords: Discriminant analysis (LDA, QDA, RDA); Petroleum (crude oil); Biofuel (biodiesel, bioethanol, ethanol–gasoline fuel); Soft independent modeling of class analogy; K; -Nearest neighbor method; Support vector machine; Probabilistic neural network; Near infrared spectroscopy
Electrochemical characterization of a single-walled carbon nanotube electrode for detection of glucose by Xuan-Hung Pham; Minh-Phuong Ngoc Bui; Cheng Ai Li; Kwi Nam Han; Jun Hee Kim; Hoshik Won; Gi Hun Seong (pp. 36-40).
We developed glucose biosensing electrodes using single-walled carbon nanotube (SWCNT) films on flexible, transparent poly(ethylene terephthalate). The homogeneous SWCNT films were fabricated by a vacuum filtration method, and the averaged resistivity and transparency of the fabricated flexible SWCNT films were 400Ωsq−1 and 80%, respectively. The glucose sensing electrodes were constructed by encapsulating glucose oxidase (GOx) by Nafion binder into the SWCNT film, and the variation in current response as a function of enzyme loading amount, Nafion thickness were investigated. 30mgmL−1 GOx and 2% Nafion was optimal for the detection of glucose. When ferrocene monocarboxylic acid (FMCA) was introduced as diffusional electron mediator, the current responses toward glucose of the Nafion/GOx/SWCNT electrodes in glucose solution containing FMCA were dramatically improved, and the developed sensor was independent of oxygen. In the application of GOx immobilized SWCNT films for glucose detection, a linear electrical response was observed for concentrations ranging from 0.25 to 3.0mM, and the detection limit and the sensitivity were assessed to be 97μM and 9.32μAmM−1cm−2, respectively. Moreover, according to the Lineweaver–Burk plot, the apparent Michaelis–Menten constant was calculated to be 23.8mM, and the current responses did not interfere with coexisting electroactive species, indicating that Nafion is an effective permselective polymer barrier.
Keywords: Single-walled carbon nanotube; Glucose detection; Amperometric sensor; Nafion
Optimization and validation of liquid–liquid extraction with low temperature partitioning for determination of carbamates in water by Simone Machado Goulart; Renata Domingos Alves; Antônio Augusto Neves; José Humberto de Queiroz; Tamires Condé de Assis; Maria Eliana L.R. de Queiroz (pp. 41-47).
Using a 23 experimental design, liquid–liquid extraction with low temperature partitioning (LLE-LTP) was optimized and validated for analysis of three carbamates (aldicarb, carbofuran and carbaryl) in water samples. In this method, 2.0mL of sample is placed in contact with 4.0mL of acetonitrile. After agitation, the sample is placed in a freezer for 3h for phase separation. The organic extract is analyzed by high performance liquid chromatography with ultraviolet detection (HPLC-UV). For validation of the technique, the following figures of merit were evaluated: accuracy, precision, detection and quantification limits, linearity, sensibility and selectivity. Extraction recovery percentages of the carbamates aldicarb, carbofuran and carbaryl were 90%, 95% and 96%, respectively. Even though extremely low volumes of sample and solvent were used, the extraction method was selective and the detection and quantification limits were between 5.0 and 10.0μgL−1, and 17.0 and 33.0μgL−1, respectively.
Keywords: Carbamates; Water; Low temperature partitioning; Aldicarb; Carbofuran; Carbaryl
Induced lead binding phytochelatins in Brassica juncea and Sesuvium portulacastrum investigated by orthogonal chromatography inductively coupled plasma-mass spectrometry and matrix assisted laser desorption ionization-time of flight-mass spectrometry by H. Zaier; A. Mudarra; D. Kutscher; M.R. Fernández de la Campa; C. Abdelly; A. Sanz-Medel (pp. 48-54).
The accumulation and transport of lead in Brassica juncea and Sesuvium portulacastrum plants and the possible formation of complexes of this element with bioligands such as phytochelatins was studied in roots and shoots of plants exposed to different amounts of Pb(NO3)2. Speciation studies on the plant extracts were conducted using size exclusion liquid chromatography and ion pair liquid chromatography coupled to UV and ICP-MS to monitor lead and sulphur. The identification of the species separated by chromatography was performed by MALDI-TOF-MS. In both types of exposed plants it was possible to identify the presence of the phytochelatin isoform PC3. The results obtained suggest that both types of plants can be useful in studies of phytoremediation but the ability of S. portulacastrum to accumulate and redistribute Pb from root to shoot is more effective than B. juncea.
Keywords: Speciation; Lead; Phytochelatins; Phytoremediation; Inductively coupled plasma-mass spectrometry; Matrix assisted laser desorption ionization-time of flight-mass spectrometry
Optimisation of specialty malt volatile analysis by headspace solid-phase microextraction in combination with gas chromatography and mass spectrometry by Sem M.G. Vandecan; Daan Saison; Nina Schouppe; Filip Delvaux; Freddy R. Delvaux (pp. 55-60).
The objective of this study was to develop a technique for analysing 14 flavour components, relevant for specialty malts. Therefore, a method was developed for the analysis of these components in dry ground malt using headspace solid-phase microextraction coupled with gas chromatography and mass spectrometry. A procedure was optimised for the optimal amount of sample, fibre selection, extraction temperature and extraction time. Afterwards, the method was calibrated and validated by the quantification of the specialty malt flavour components in a colour, a caramel and a roasted malt.
Keywords: Solid-phase microextraction; Gas chromatography; Mass spectrometry; Dry matrix; Specialty malt; Flavour
Ultra-trace determination of plutonium in marine samples using multi-collector inductively coupled plasma mass spectrometry by Patric Lindahl; Miranda Keith-Roach; Paul Worsfold; Min-Seok Choi; Hyung-Seon Shin; Sang-Hoon Lee (pp. 61-69).
Sources of plutonium isotopes to the marine environment are well defined, both spatially and temporally, which makes Pu a potential tracer for oceanic processes. This paper presents the selection, optimisation and validation of a sample preparation method for the ultra-trace determination of Pu isotopes (240Pu and239Pu) in marine samples by multi-collector (MC) ICP-MS. The method was optimised for the removal of the interference from238U and the chemical recovery of Pu. Comparison of various separation strategies using AG1-X8, TEVA, TRU, and UTEVA resins to determine Pu in marine calcium carbonate samples is reported. A combination of anion-exchange (AG1-X8) and extraction chromatography (UTEVA/TRU) was the most suitable, with a radiochemical Pu yield of 87±5% and a U decontamination factor of 1.2×104. Validation of the method was accomplished by determining Pu in various IAEA certified marine reference materials. The estimated MC-ICP-MS instrumental limit of detection for239Pu and240Pu was 0.02fgmL−1, with an absolute limit of quantification of 0.11fg. The proposed method allows the determination of ultra-trace Pu, at femtogram levels, in small size marine samples (e.g., 0.6–2.0g coral or 15–20L seawater). Finally, the analytical method was applied to determining historical records of the Pu signature in coral samples from the tropical Northwest Pacific and239+240Pu concentrations and240Pu/239Pu atom ratios in seawater samples as part of the 2008 GEOTRACES intercalibration exercise.
Keywords: Multi-collector inductively coupled plasma mass spectrometry; Plutonium; Coral; Sediment; Seawater; Isotope dilution
Enzyme-linked immunosorbent assays for doping control of 5α-reductase inhibitors finasteride and dutasteride by Eva M. Brun; Ana Torres; Rosa Ventura; Rosa Puchades; Ángel Maquieira (pp. 70-79).
Finasteride and dutasteride are 5α-reductase inhibitors included in the World Anti-Doping Agency's list of banned substances. Two highly sensitive and selective ELISA assays were developed for these compounds. Polyclonal rabbit antibodies were raised using synthesized haptens and other commercial products. The best immunoassay obtained, based on an antibody-coated format, showed a limit of detection of 0.01μgL−1 and an IC50 of 0.75μgL−1 for finasteride (cross-reactivity with dutasteride<4%). The second assay allowed finasteride and dutasteride determination, with limits of detection of 0.013 and 0.021μgL−1, and IC50 values 0.18 and 1.18μgL−1, respectively. Both assays were highly selective to a set of anabolic steroids, but they showed 37% and 30% cross-reactivity with the major urinary metabolite of finasteride, allowing its determination. The developed ELISA had better sensitivity than HPLC/MS/MS method and was applied as a screening technique to quantify dutasteride, finasteride, and its main metabolite in human urine without sample pre-treatment. Moreover, the analysis of dutasteride's excretion urines by ELISA was used to obtain its human excretion rate, essential to improve the analytical strategies about this type of drugs (permitted as medicines and prohibited in sport) and to establish an effective anti-doping policy.
Keywords: Finasteride; Dutasteride; 5α-Reductase inhibitors; Doping control; Enzyme-linked immunosorbent assay
A colorimetric sensor for determination of cysteine by carboxymethyl cellulose-functionalized gold nanoparticles by Xiaoyi Wei; Li Qi; Junjun Tan; Ruigang Liu; Fuyi Wang (pp. 80-84).
A simple and sensitive colorimetric method for cysteine detection was established based on the carboxymethyl cellulose-functionalized gold nanoparticles (CMC-AuNPs). The nanoparticles were directly synthesized with sodium carboxymethyl cellulose by a simple approach, which would protect particles against salt-induced aggregation. Then the CMC-AuNPs solution exhibited a high colorimetric selectivity to cysteine. The assay results indicated that the introduction of cysteine could induce the aggregation of the colloidal solutions at the presence of sodium chloride, displaying changes in color and in UV–vis absorption spectra. Thus an exceptionally simple, rapid method for detecting cysteine was obtained at the linear range of 10.0–100.0μM with the relative coefficient of 0.997. The proposed method possessed the advantages of simplicity and sensitivity, and was applied to real urine sample detection. The results were satisfying and the proposed method was especially appropriate for detection of cysteine in biological samples.
Keywords: Gold nanoparticles; Carboxymethyl cellulose; Cysteine; Colorimetric sensor; Urine
Characterization of the gas sensors based on polymer-coated resonant microcantilevers for the detection of volatile organic compounds by Ying Dong; Wei Gao; Qin Zhou; Yi Zheng; Zheng You (pp. 85-91).
The gas sensors based on polymer-coated resonant microcantilevers for volatile organic compounds (VOCs) detection are investigated. A method to characterize the gas sensors through sensor calibration is proposed. The expressions for the estimation of the characteristic parameters are derived. The effect of the polymer coating location on the sensor's sensitivity is investigated and the formula to calculate the polymer–analyte partition coefficient without knowing the polymer coating features is presented for the first time. Three polymers: polyethyleneoxide (PEO), polyethylenevinylacetate (PEVA) and polyvinylalcohol (PVA) are used to perform the experiments. Six organic solvents: toluene, benzene, ethanol, acetone, hexane and octane are used as analytes. The response time, reversibility, hydrophilicity, sensitivity and selectivity of the polymer layers are discussed. According to the results, highly sensitive sensors for each of the analytes are proposed. Based on the characterization method, a convenient and flexible way to the construction of electric nose system by the polymer-coated resonant microcantilevers can be achieved.
Keywords: Gas sensor; Microcantilever; Polymer; Volatile organic compound
Printed protein microarrays on unmodified plastic substrates by Meike Moschallski; Johannes Baader; Oswald Prucker; Jürgen Rühe (pp. 92-98).
A key challenge for the generation of protein microarrays is the immobilization of functional capture probe proteins at the chip surfaces. Here, a new concept for a single step production of protein microarrays to unmodified plastic substrates is presented. It is based on the printing of polymer/protein mixtures and the photochemical attachment of the obtained microstructures to the plastic chip surfaces. In the photochemical process three reactions occur simultaneously: transformation of the polymer into hydrogel dots, covalent binding of the forming gel to the substrate, and covalent immobilization of the proteins to the three-dimensional hydrogel scaffold. As an example we use anti-bovine serum albumin as a protein (anti-BSA) and a water swellable polymer network based on polydimethylacrylamide as a scaffold, which is photochemically crosslinked using benzophenone as a crosslinking agent. In one series of microarray experiments the probe density of the immobilized proteins was determined by incorporating fluorescence-labeled anti-BSA in the hydrogels. In a typical experiment, the number of immobilized probes was determined to 4×109 protein molecules per spot. In other experiments, the microarrays were brought into contact with fluorescently labeled BSA. In such analyses signal-to-noise values of more than 200 were obtained and about 9×107 antigen molecules were bound per spot. This demonstrates that in a very simple way microarrays with large amount of probes per spot can be realized and that antibodies immobilized in the printed hydrogels remain accessible and retain their functionality.
Keywords: Abbreviations; GOPS; 3-glycidoxypropyltrimethoxy-silane; His; histidine; MABP; methacryloyloxybenzophenone; MAGE; methacrylic acid glycidylester; NaPi; sodium phosphate buffer; NHS; N-hydroxysuccinimide; OWS; optical waveguide spectroscopy; PDMAA; polydimethylacrylamide; PMMA; polymethylmethacrylate; SSC; sodium citrate buffer; VPA; vinyl phosphonic acidProtein immobilization; Plastic chips; Microarray; Polymer networks