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Analytica Chimica Acta (v.618, #2)
Discrimination of Ganoderma lucidum according to geographical origin with near infrared diffuse reflectance spectroscopy and pattern recognition techniques by Yi Chen; Ming-Yong Xie; Yan Yan; Shang-Bin Zhu; Shao-Ping Nie; Chang Li; Yuan-Xing Wang; Xiao-Feng Gong (pp. 121-130).
A rapid and nondestructive near infrared (NIR) method combined with chemometrics was used to discriminate Ganoderma lucidum according to cultivation area. Raw, first, and second derivative NIR spectra were compared to develop a robust classification rule. The chemical properties of G. lucidum samples were also investigated to find out the difference between samples from six varied origins. It could be found that the amount of polysaccharides and triterpenoid saponins in G. lucidum samples was considerably different based on cultivation area. These differences make NIR spectroscopic method viable. Principal component analysis (PCA), discriminant partial least-squares (DPLS) and discriminant analysis (DA) were applied to classify the geographical origins of those samples. The results showed that excellent classification could be obtained after optimizing spectral pre-treatment. For the discriminating of samples from three different provinces, DPLS provided 100% correct classifications. Moreover, for samples from six different locations, the correct classifications of the calibration as well as the validation data set were 96.6% using the DA method after the SNV first derivative spectral pre-treatment. Overall, NIR diffuse reflectance spectroscopy using pattern recognition was shown to have significant potential as a rapid and accurate method for the identification of herbal medicines.
Keywords: Near infrared spectroscopy; Discrimination; Geographical origin; Ganoderma lucidum; Pattern recognition
Adsorptive stripping square wave voltammetry (Ad-SSWV) accomplished with second-order multivariate calibration by T. Galeano-Díaz; A. Guiberteau-Cabanillas; A. Espinosa-Mansilla; M.D. López-Soto (pp. 131-139).
A method, using stripping square wave voltammetry (Ad-SSWV), for the simultaneous determination of fenitrothion (FEN) and its metabolites: fenitrooxon (OXON) and 3-methyl-4-nitrophenol (3-MET) in environmental samples is reported. All three compounds produce, at mercury electrode (HMDE), an electrochemical signal due to an adsorptive–reductive process. The electrochemical approach shows a very high overlap degree for FEN and OXON voltammograms, however the adsorption kinetic profile could be used as an additional differential variable between both analytes. Second-order multivariate calibration has been tested to solve the mixture of the three compounds. The second-order assayed methods were parallel factor analysis (PARAFAC), unfolded partial least squares (U-PLS), multidimensional partial least squares (N-PLS) and the latest ones were used in combination with the residual bilinearization procedure RBL. U-PLS/RBL model was stated as the best second-order algorithm for the simultaneous determination of these three compounds up to 50ngmL−1 for each analyte. The detection limits and recovery values were 1.6ngmL−1 and 92±7% for FEN; 3.7ngmL−1 and 101±9% for OXON and 0.6ngmL−1 and 97±8% for 3-MET.
Keywords: Fenitrothion; Metabolites; Adsorptive stripping square wave voltammetry; Second-order multivariate calibration; Unfolded partial least squares/residual bilinearization
Electroreduction of oxygen on gold nanoparticle/PDDA-MWCNT nanocomposites in acid solution by Nadezda Alexeyeva; Kaido Tammeveski (pp. 140-146).
The electrochemical reduction of oxygen has been studied on gold nanoparticle (AuNP)/poly(diallyldimethylammonium chloride) (PDDA)-multi-walled carbon nanotubes (MWCNTs) modified glassy carbon (GC) electrodes in 0.5M H2SO4 using the rotating disk electrode (RDE) technique. The AuNP/PDDA-MWCNT catalysts were prepared using an electrostatic layer-by-layer (LBL) technique. The composite electrode was electrochemically characterized by cyclic voltammetry in an O2-free electrolyte. The oxygen reduction behaviour of these electrodes was compared with that of a PDDA-MWCNT/GC electrode. The AuNP/PDDA-MWCNT catalysts showed a remarkable electrocatalytic activity towards O2 reduction in acid media. The half-wave potential of O2 reduction on the AuNP/PDDA-MWCNT catalyst shifted more than 200mV to more positive potentials as compared to that of a PDDA-MWCNT/GC electrode. The kinetic parameters of O2 reduction were determined and the specific activity of the hybrid electrodes was higher than that of bulk gold.
Keywords: Oxygen reduction; Electrocatalysis; Gold nanoparticles; Multi-walled carbon nanotubes; Poly(diallyldimethylammonium chloride)
Synthesis of surface molecularly imprinted silica micro-particles in aqueous solution and the usage for selective off-line solid-phase extraction of 2,4-dinitrophenol from water matrixes by Wei Luo; Lihua Zhu; Chen Yu; Heqing Tang; Hongxia Yu; Xue Li; Xu Zhang (pp. 147-156).
Very severe reaction conditions are required in the conventional synthesis of molecularly imprinted polymers (MIPs), which is unfavorable to their applications in chemical separation and analysis. A simple surface molecular imprinting approach was developed to synthesize MIP-coated SiO2 micro-particles in aqueous solutions. The1H NMR and UV–vis spectroscopic analysis indicated that via hydrogen bonding, the functional monomer ( o-phenylenediamine) can associate with the target (template) 2,4-dinitrophenol (2,4-DNP), as a model compound of organic pollutants, to form a precursor in aqueous solution. The copolymerization of this precursor and the free monomer was performed in the aqueous suspension of surface modified SiO2 particles, leading to the formation of MIP-coated SiO2 micro-particles. The MIP-coated silica particles were characterized with FT-IR, TGA, and UV–vis solid-state reflection spectroscopy, and were further demonstrated to have high adsorption capacity, excellent selectivity and site accessibility for 2,4-DNP. The new absorbent was successfully used in solid-phase extraction (SPE) to selectively enrich and determine 2,4-DNP in aqueous samples. The experimental results indicated that the MIP-SPE column yielded recoveries higher than 92% with R.S.D. <2.8%, much better than the commercial C18-SPE column, which produced a recovery less than 30% with R.S.D. <3.0%.
Keywords: Molecularly imprinted polymer; Synthesis; Solid-phase extraction; 2,4-Dinitrophenol; High-performance liquid chromatography
Calibration and use of the Chemcatcher® passive sampler for monitoring organotin compounds in water by R. Aguilar-Martínez; M.A. Palacios-Corvillo; R. Greenwood; G.A. Mills; B. Vrana; M.M. Gómez-Gómez (pp. 157-167).
An integrative passive sampler (Chemcatcher®) consisting of a 47mm C18 Empore™ disk as the receiving phase overlaid with a thin cellulose acetate diffusion membrane was developed and calibrated for the measurement of time-weighted average water concentrations of organotin compounds [monobutyltin (MBT), dibutyltin (DBT), tributlytin (TBT) and triphenyltin (TPhT)] in water. The effect of water temperature and turbulence on the uptake rate of these analytes was evaluated in the laboratory using a flow-through tank. Uptake was linear over a 14-day period being in the range: MBT (3–23mLday−1), DBT (40–200mLday−1), TBT (30–200mLday−1) and TPhT (30–190mLday−1) for all the different conditions tested. These sampling rates were high enough to permit the use of the Chemcatcher® to monitor levels of organotin compounds typically found in polluted aquatic environments. Using gas chromatography (GC) with either ICP-MS or flame photometric detection, limits of detection for the device (14-day deployment) for the different organotin compounds in water were in the range of 0.2–7.5ngL−1, and once accumulated in the receiving phase the compounds were stable over prolonged periods. Due to anisotropic exchange kinetics, performance reference compounds could not be used with this passive sampling system to compensate for changes in sampling rate due to variations in water temperature, turbulence and biofouling of the surface of the diffusion membrane during field deployments. The performance of the Chemcatcher® was evaluated alongside spot water sampling in Alicante Habour, Spain which is known to contain elevated levels of organotin compounds. The samplers provided time-weighted average concentrations of the bioavailable fractions of the tin compounds where environmental concentrations fluctuated markedly in time.
Keywords: Passive sampling; Chemcatcher; ®; Organotin compounds; Water; Pollution; Monitoring; Priority pollutants
Mass spectrometric identification of formaldehyde-induced peptide modifications under in vivo protein cross-linking conditions by Judy Toews; Jason C. Rogalski; Thomas J. Clark; Juergen Kast (pp. 168-183).
Formaldehyde cross-linking of proteins is emerging as a novel approach to study protein–protein interactions in living cells. It has been shown to be compatible with standard techniques used in functional proteomics such as affinity-based protein enrichment, enzymatic digestion, and mass spectrometric protein identification. So far, the lack of knowledge on formaldehyde-induced protein modifications and suitable mass spectrometric methods for their targeted detection has impeded the identification of the different types of cross-linked peptides in these samples. In particular, it has remained unclear whether in vitro studies that identified a multitude of amino acid residues reacting with formaldehyde over the course of several days are suitable substitutes for the much shorter reaction times of 10–20min used in cross-linking experiments in living cells. The current study on model peptides identifies amino-termini as well as lysine, tryptophan, and cysteine side chains, i.e. a small subset of those modified after several days, as the major reactive sites under such conditions, and suggests relative position in the peptide sequence as well as sequence microenvironment to be important factors that govern reactivity. Using MALDI-MS, mass increases of 12Da on amino groups and 30Da on cysteines were detected as the major reaction products, while peptide fragment ion analysis by tandem mass spectrometry was used to localize the actual modification sites on a peptide. Non-specific cross-linking was absent, and could only be detected with low yield at elevated peptide concentrations. The detailed knowledge on the constraints and products of the formaldehyde reaction with peptides after short incubation times presented in this study is expected to facilitate the targeted mass spectrometric analysis of proteins after in vivo formaldehyde cross-linking.
Keywords: Protein cross-linking; Formaldehyde; Chemical modification; Mass spectrometry; Peptide fragmentation; Reactivity
Precursor ion scanning–mass spectrometry for the determination of nitro functional groups in atmospheric particulate organic matter by Julien Dron; Ehgere Abidi; Imad El Haddad; Nicolas Marchand; Henri Wortham (pp. 184-195).
An analytical method for the quantitative determination of the total nitro functional group (R-NO2) content in atmospheric particulate organic matter is developed. The method is based on the selectivity of NO2− ( m/ z 46) precursor ion scanning (PAR 46) by atmospheric pressure chemical ionization–tandem mass spectrometry (APCI–MS/MS). PAR 46 was experimented on 16 nitro compounds of different molecular structures and was compared with a neutral loss of NO (30amu) technique in terms of sensitivity and efficiency to characterize the nitro functional groups. Covering a wider range of compounds, PAR 46 was preferred and applied to reference mixtures containing all the 16 compounds under study. Repeatability carried out using an original statistical approach, and calibration experiments were performed on the reference mixtures proven the suitability of the technique for quantitative measurements of nitro functional groups in samples of environmental interest with good accuracy. A linear range was obtained for concentrations ranging between 0.005 and 0.25mM with a detection limit of 0.001mM of nitro functional groups. Finally, the analytical error based on an original statistical approach applied to numerous reference mixtures was below 20%. Despite of potential artifacts related to nitro-alkanes and organonitrates, this new methodology offers a promising alternative to FT-IR measurements. The relevance of the method and its potentialities are demonstrated through its application to aerosols collected in the EUPHORE simulation chamber during o-xylene photooxidation experiments and in a suburban area of a French alpine valley during summer.
Keywords: Functional group analysis; Tandem mass spectrometry; Precursor ion scanning; Nitro compounds; Particulate organic matter
Non-targeted detection of chemical contamination in carbonated soft drinks using NMR spectroscopy, variable selection and chemometrics by Adrian J. Charlton; Paul Robb; James A. Donarski; John Godward (pp. 196-203).
An efficient method for detecting malicious and accidental contamination of foods has been developed using a combined1H nuclear magnetic resonance (NMR) and chemometrics approach. The method has been demonstrated using a commercially available carbonated soft drink, as being capable of identifying atypical products and to identify contaminant resonances. Soft-independent modelling of class analogy (SIMCA) was used to compare1H NMR profiles of genuine products (obtained from the manufacturer) against retail products spiked in the laboratory with impurities. The benefits of using feature selection for extracting contaminant NMR frequencies were also assessed. Using example impurities (paraquat, p-cresol and glyphosate) NMR spectra were analysed using multivariate methods resulting in detection limits of approximately 0.075, 0.2, and 0.06mM for p-cresol, paraquat and glyphosate, respectively. These detection limits are shown to be approximately 100-fold lower than the minimum lethal dose for paraquat. The methodology presented here is used to assess the composition of complex matrices for the presence of contaminating molecules without a priori knowledge of the nature of potential contaminants. The ability to detect if a sample does not fit into the expected profile without recourse to multiple targeted analyses is a valuable tool for incident detection and forensic applications.
Keywords: Nuclear magnetic resonance; Contaminant; Chemometrics; Variable selection
A novel gaseous pinacolyl alcohol sensor utilizing cataluminescence on alumina nanowires prepared by supercritical fluid drying by Chao Yu; Guohong Liu; Boli Zuo; Yongjun Tang; Tian Zhang (pp. 204-209).
A cataluminescence (CTL) sensor using Al2O3 nanowires as the sensing material was developed for the determination of trace pinacolyl alcohol in air samples based on the catalytic chemiluminescence (CL) of pinacolyl alcohol on Al2O3 nanowires. Eight catalysts were examined and the CL intensity on Al2O3 nanowires prepared by supercritical fluid drying was the strongest. This novel CL sensor showed high sensitivity and selectivity to gaseous pinacolyl alcohol at optimal temperature of 340°C. Quantitative analysis was performed at a wavelength of 460nm. The linear range of CTL intensity versus concentration of gaseous pinacolyl alcohol was 0.09×10−6 to 2.56×10−6gmL−1 ( r=0.9983, n=6) with a detection limit (3 σ) of 0.0053×10−6gmL−1. None or only very low levels of interference were observed while the foreign substances such as water vapor, ethanol, ammonia, chloroform, benzene, nitrogen dioxide, methylbenzene, hydrochloric acid, methanol and butanol were passing through the sensor. The response time of the sensor is less than 100s, and the sensor had a long lifetime more than 60h. The sensor would be potentially applied to analysis of the nerve agents such as Soman.
Keywords: Cataluminescence; Al; 2; O; 3; nanowires; Sensor; Pinacolyl alcohol
Selective and sensitive determination of lipoyllysine (protein-bound α-lipoic acid) in biological specimens by high-performance liquid chromatography with fluorescence detection by Soichiro Satoh; Masahiro Shindoh; Jun Zhe Min; Toshimasa Toyo’oka; Takeshi Fukushima; Shinsuke Inagaki (pp. 210-217).
The direct determination of lipoyllysine (LLys) in proteins was carried out by reversed-phase high-performance liquid chromatography with fluorescence (FL) detection. The proteins containing α-lipoic acid (LA) were first hydrolyzed with several enzymes such as pronase E and subtilisin A. The disulfide bond (–S–S–) in LLys liberated from the enzyme digestion was reduced with tris(2-carboxyethyl)phosphine to the thiol form (–SH). The reduced LLys was then labeled with ammonium 4-fluoro-2,1,3-benzoxadiazole-7-sulfonate (SBD-F) at 50°C for 1h. The resulting fluorophore, SBD-LLys, was separated by reversed-phase chromatography and fluorometrically detected at 510nm (excitation at 380nm). The calibration curve obtained from the peak areas versus the injection amounts of LLys showed a good linearity. The limits of detection and quantification of LLys on the chromatogram were approximately 0.13pmol (signal-to-noise ratio (S/N)=3) and 0.44pmol (S/N=10), respectively. A good recovery (98.9–107.1%) and precision (R.S.D.: 4.49–17.2%) of LLys were also obtained using the present procedure. The proposed method was used for the determination of LLys in spinach and animal tissues. The FL derivative was completely separated without any interference by endogenous substances in the sample and sensitively detected by the fluorimetry. The assay values of LLys per 1g wet tissues were 3.67μg (kidney), 1.97μg (liver), 2.09μg (heart), 0.59μg (brain), 0.30μg (lung), 0.38μg (pancreas), and 0.20μg (spleen). The direct determination of LLys in protein using the FL labeling method is reported for the first time.
Keywords: Lipoyllysine; α-Lipoic acid; Enzyme digestion; Fluorescence labeling of thiol; Ammonium 4-fluoro-2,1,3-benzoxadiazole-7-sulfonate; High-performance liquid chromatography with fluorescence detection
Development of an enzyme-linked immunosorbent assay (ELISA)-like fluorescence assay to investigate the interactions of glycosaminoglycans to cells by Rodrigo Ippolito Bouças; Edvaldo S. Trindade; Ivarne L.S. Tersariol; Carl P. Dietrich; Helena B. Nader (pp. 218-226).
Sulfated glycosaminoglycans were labeled with biotin to study their interaction with cells in culture. Thus, heparin, heparan sulfate, chondroitin 4-sulfate, chondroitin 6-sulfate and dermatan sulfate were labeled using biotin-hydrazide, under different conditions. The structural characteristics of the biotinylated products were determined by chemical (molar ratios of hexosamine, uronic acid, sulfate and biotin) and enzymatic methods (susceptibility to degradation by chondroitinases and heparitinases). The binding of biotinylated glycosaminoglycans was investigated both in endothelial and smooth muscle cells in culture, using a novel time resolved fluorometric method based on interaction of europium-labeled streptavidin with the biotin covalently linked to the compounds. The interactions of glycosaminoglycans were saturable and number of binding sites could be obtained for each individual compound. The apparent dissociation constant varied among the different glycosaminoglycans and between the two cell lines. The interactions of the biotinylated glycosaminoglycans with the cells were also evaluated using confocal microscopy. We propose a convenient and reliable method for the preparation of biotinylated glycosaminoglycans, as well as a sensitive non-competitive fluorescence-based assay for studies of the interactions and binding of these compounds to cells in culture.
Keywords: Abbreviations; BSA; bovine serum albumin; C4S; chondroitin 4-sulfate; C6S; chondroitin 6-sulfate; DAB; 3,3′-diamino benzamidine tetrahydrochloride; DAPI; 4′,6-diamidino-2-phenylindole dihydrochloride; DS; dermatan sulfate; ECM; extracellular matrix; EDC; (1-ethyl-3-[dimethylaminopropyl] carbodiimide hydrochloride); EC; endothelial cells; FCS; fetal calf serum; HRP; horseradish peroxidase; HS; heparan sulfate; Hep; heparin; GAG; glycosaminoglycan; bGAG; biotinylated GAG; PBS; phosphate buffer saline; SMC; smooth muscle cellsGlycosaminoglycans; Biotinylation procedures; Fluorescence; Endothelial cells; Smooth muscle cells
Simultaneous determination of cell aging and ATP release from erythrocytes and its implications in type 2 diabetes by Wasanthi Subasinghe; Dana M. Spence (pp. 227-233).
Glucose-6-phosphate dehydrogenase (G6PD) is a determinant in the antioxidant status of the red blood cell (RBC) and is also used as an indicator of cell age. However, it is unknown if the relationship among antioxidant status, cell age, and RBC-derived adenosine triphosphate (ATP) occurs immediately or over a period of time. Therefore, the development of a simultaneous determination of G6PD activity (via the determination of nicotinamide adenine dinucleotide phosphate (NADPH)) in RBCs and the determination of deformation-induced RBC-derived ATP is described. The NADPH and ATP were determined while undergoing a chemically induced aging process via inhibition of G6PD with dehydroepiandroesterone (DHEA). Upon incubation with DHEA for 30min, NADPH levels measured in a flow stream decreased to 7.96±1.10μM from an original value of 13.20±1.80μM in a 0.02% solution of RBCs. In order to demonstrate a direct relationship between G6PD activity and deformation-induced ATP release from RBCs, a simultaneous microflow determination of G6PD activity and ATP release was performed. Upon inhibition with DHEA, NADPH levels decreased to 8.62±0.29μM from its original value of 12.73±0.50μM while ATP release decreased from 0.21±0.07μM to 0.06±0.02μM. These values were validated by an examination of NADPH levels in, and ATP release from, RBC fractions containing younger and older cells (separated by cell density centrifugation). This determination provides evidence that antioxidant status in the RBC and its ability to release ATP, a known stimulus of nitric oxide production, are closely related.
Keywords: Glucose-6-phosphate dehydrogenase; Nicotinamide adenine dinucleotide phosphate; Adenosine triphosphate; Chemiluminescence; Fluorescence