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Analytica Chimica Acta (v.602, #2)
Advances in passive sampling in environmental studies by Agata Kot-Wasik; Bożena Zabiegała; Magdalena Urbanowicz; Ewa Dominiak; Andrzej Wasik; Jacek Namieśnik (pp. 141-163).
Passive sampling is based on the phenomenon of mass transport due to the difference between chemical potentials of analytes in a given environmental compartment and the collection medium inside a dosimeter. The subsequent laboratory procedure (i.e. extraction, identification and determination of analytes) is the same as in the case of classic sampling techniques.Passive sampling techniques are characterized by simplicity with regard to the dosimeter's construction as well as its maintenance. Therefore, they find ever increasing application in the field of environmental research and analytics. When choosing a passive sampling method, one should not forget that some passive samplers require the time-consuming calibration step before being used in the field.Novel solutions and modifications of existing sampler designs have been presented. Practical application of passive dosimetry in environmental analytics, including sampling of water, soil, air and other atypical media are discussed. Some aspects of calibration methods in passive dosimetry are also described. The latest trends in the application of passive sampling are highlighted.
Keywords: Passive sampling; Dosimeters; Air; Water; Soil; Environmental monitoring
Review on modelling aspects in reversed-phase liquid chromatographic quantitative structure–retention relationships by R. Put; Y. Vander Heyden (pp. 164-172).
In the literature an increasing interest in quantitative structure–retention relationships (QSRR) can be observed. After a short introduction on QSRR and other strategies proposed to deal with the starting point selection problem prior to method development in reversed-phase liquid chromatography, a number of interesting papers is reviewed, dealing with QSRR models for reversed-phase liquid chromatography. The main focus in this review paper is put on the different modelling methodologies applied and the molecular descriptors used in the QSRR approaches. Besides two semi-quantitative approaches (i.e. principal component analysis, and decision trees), these methodologies include artificial neural networks, partial least squares, uninformative variable elimination partial least squares, stochastic gradient boosting for tree-based models, random forests, genetic algorithms, multivariate adaptive regression splines, and two-step multivariate adaptive regression splines.
Keywords: Quantitative structure–retention relationships; Molecular descriptors; Retention prediction; Reversed-phase chromatography
The miniaturization of bioanalytical assays and sample pretreatments by exploiting meso-fluidic lab-on-valve configurations: A review by Xu-Wei Chen; Jian-Hua Wang (pp. 173-180).
Termed as the third generation of flow injection analysis, the lab-on-valve (LOV) system is closely related to the principle of sequential injection analysis and constructed aiming at facilitating various miniature analytical operations and downscaling sample/reagent consumption. The highly integrated configuration makes LOV system compatible with virtually all kinds of spectroscopic detection techniques and presents it an intelligent platform for bead-injection protocol. The minimized reagent consumption and precise fluidic manipulation also propose the LOV system an excellent candidate for the adaptation of sample processing in the macroscopic world with the microfluidic analysis system. After a few years development, it has been applied extensively in the miniaturization and automation of analytical procedures, especially in the field of bioassays. This review presents the up-to-date progress and some of the selected applications of the LOV system for bioanalytical assays. In addition, future perspectives are discussed.
Keywords: Lab-on-valve; Sequential injection analysis; Bead injection; Bioanalytical assays
Direct electron transfer of xanthine oxidase and its catalytic reduction to nitrate by Yunhua Wu; Shengshui Hu (pp. 181-186).
This work reports on the direct electrochemistry of the xanthine oxidase (XO) from buttermilk, a mononuclear molybdenum enzyme that comprises four redox active cofactors: a five-coordinate mononuclear Mo ion, two [2Fe-2S] clusters, and a flavin adenine dinucleotide (FAD) group. The Mo, [2Fe-2S] and FAD redox responses are obtained from the enzyme immobilized on an activated single-wall carbon nanotubes (SWNTs) modified glassy carbon electrode using protein film voltammetry. The formal potentials of which are −0.61V, −0.47V and −0.37V (vs. SCE) at pH 5.0, respectively. Upon addition of nitrate to the electrochemical cell, a steady-state voltammogram and i– t amprometric response were observed, indicating XO can catalyze the reduction of nitrate.
Keywords: Xanthine oxidase; Nitrate; Direct electron transfer; Catalytic reduction
Electrodeposition of Co–Ag films and compositional determination by electrochemical methods by Elvira Gomez; Jose García-Torres; Elisa Valles (pp. 187-194).
An electrolytic bath containing silver(I), cobalt(II) and different complexing agents to electrodeposit Co–Ag coatings over vitreous carbon and silicon/seed-layer substrates is proposed. In situ electrochemical characterization of thin deposits is performed by means of stripping (potentiodynamic or galvanostatic) methods. These techniques allow detecting the heterogeneous codeposition of cobalt and silver. Electrochemical ex situ methods (polarographic and voltammetric methods) are implemented to quantify the silver and cobalt percentage in the coatings. Optimal analytical parameters for voltammetric method are established.
Keywords: Heterogeneous Co–Ag deposits; Electrodeposition; Voltammetry; Stripping; Polarography
An ultrasound-assisted digestion method for the determination of toxic element concentrations in ash samples by inductively coupled plasma optical emission spectrometry by Aki Ilander; Ari Väisänen (pp. 195-201).
A method of ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) used for the determination of toxic element concentrations (arsenic, barium, cobalt, copper, lead, nickel, strontium, vanadium and zinc) in ash samples was developed. All the measurements were performed in robust plasma conditions which were tested by measuring the Mg(II) 280.270nm/Mg(I) 285.213nm line intensity ratios. The highest line intensity ratios were observed when a nebulizer gas flow of 0.6Lmin−1, auxiliary gas flow of 0.2Lmin−1 and plasma power of 1400W were used for radially viewed plasma. The analysis of SRM 1633b showed that the ultrasound-assisted method developed is highly comparable with the microwave digestion method standardized by the United States Environmental Protection Agency (EPA-3052). The ultrasound-assisted digestion with a digestion solution of aqua regia and hydrofluoric acid (HF) resulted in recovery rates of over 81%. One exception is arsenic which resulted in recoveries of about 60% only; however, it could be digested with good recovery (>90%) using a digestion solution of 5mL of water and 5mL of aqua regia. The major advantage of the ultrasound-assisted digestion over microwave digestion is the high treatment rate (30 samples simultaneously with a sonication time of 18min).
Keywords: Emission spectrometry; Ultrasound; Microwave; Ash; Toxic elements
Application of microwave energy to speed up the alkaline extraction of humic and fulvic acids from marine sediments by Vanessa Romarís-Hortas; Antonio Moreda-Piñeiro; Pilar Bermejo-Barrera (pp. 202-210).
The feasibility of microwave energy to speed up the alkaline extraction of humic substances (humic acid, HA, and fulvic acid, FA) from marine sediments has been checked. Extractions were performed by using 20mL of sodium hydroxide at 0.1M (two repeated extractions) after an ultrasound-assisted acid pre-treatment of samples to remove the carbonate fraction (ultrasound power at 17kHz, 10mL of 6.0M hydrochloric acid for 15min). After separation of HA and FA fractions by acidifying with 6M HCl, the FA fraction (supernatant) was purified by passing the solution through a column of Amberlite XAD-8. Both HA and FA extracts were measured by UV–visible spectrophotometry. All variables affecting the extraction process (sodium hydroxide concentration and volume, ramp and hold times, temperature and number of repeated extractions) have been screened by using a Plackett–Burman design (PBD) as multivariate approach. The variables temperature and number of repeated extractions were the most significant factors ( P=95%) affecting the extraction of both FA and HA from marine sediments. These two variables have led optimum values of 150°C and two repeated extractions. The developed method has been found precise (R.S.D.s of 9% for HA and 12% for FA, for 11 determinations) and its results were comparable in terms of elemental (C, H and N) composition to those obtained after applying methods based on mechanical stirring and ultrasounds assisting. However, higher HA and FA concentrations than those obtained after conventional stirring and ultrasound irradiation were obtained when applying microwave energy. This means a higher efficiency of microwave energy than ultrasounds or mechanical stirring to extract HA and FA fractions from marine sediments. The method was finally applied to different surface marine sediments from the Ría de Arousa estuary.
Keywords: Humic substances; Marine sediments; UV–visible spectrophotometry; Microwave energy
Extraction of polycyclic aromatic hydrocarbons and organochlorine pesticides from soils: A comparison between Soxhlet extraction, microwave-assisted extraction and accelerated solvent extraction techniques by Wentao Wang; Bingjun Meng; Xiaoxia Lu; Yu Liu; Shu Tao (pp. 211-222).
The methods of simultaneous extraction of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) from soils using Soxhlet extraction, microwave-assisted extraction (MAE) and accelerated solvent extraction (ASE) were established, and the extraction efficiencies using the three methods were systemically compared from procedural blank, limits of detection and quantification, method recovery and reproducibility, method chromatogram and other factors. In addition, soils with different total organic carbon contents were used to test the extraction efficiencies of the three methods. The results showed that the values obtained in this study were comparable with the values reported by other studies. In some respects such as method recovery and reproducibility, there were no significant differences among the three methods for the extraction of PAHs and OCPs. In some respects such as procedural blank and limits of detection and quantification, there were significant differences among the three methods. Overall, ASE had the best extraction efficiency compared to MAE and Soxhlet extraction, and the extraction efficiencies of MAE and Soxhlet extraction were comparable to each other depending on the property such as TOC content of the studied soil. Considering other factors such as solvent consumption and extraction time, ASE and MAE are preferable to Soxhlet extraction.
Keywords: Soxhlet extraction; Microwave-assisted extraction; Accelerated solvent extraction; Polycyclic aromatic hydrocarbons; Organochlorine pesticides; Soil
Sensitive determination of fungicides and prometryn in environmental water samples using multiwalled carbon nanotubes solid-phase extraction cartridge by Qingxiang Zhou; Junping Xiao; Yujie Ding (pp. 223-228).
In this paper, a sensitive, fast and simple method with multiwalled carbon nanotubes SPE for the determination of metalaxyl, diethofencarb, myclobutanil, prometryn and tebuconazole was developed. Factors that may influence the extraction efficiency of MWCNTs such as the kind and volume of eluent, pH of sample solutions and sample volume were optimized. Under the optimized conditions, detection limits for metalaxyl, diethofencarb, myclobutanil, prometryn and tebuconazole were in the range of 2.99–6.94ngL−1, respectively. There was good linearity in the concentration range of 0.2–80μgL−1 except that prometryn was in the range of 0.05–20μgL−1. The precisions of proposed method were very excellent in the range of 1.43–5.86%. The method was successfully applied to the analysis of environmental water samples, and the results indicated that it could be used as a good alternative for the routine analysis in environmental field.
Keywords: Multiwalled carbon nanotubes; Solid-phase extraction; Metalaxyl; Diethofencarb; Myclobutanil; Prometryn and tebuconazole
Single DNA molecules as probes for interrogating silica surfaces after various chemical treatments by Xia Liu; Zhan Wu; Huagui Nie; Ziling Liu; Yan He; E.S. Yeung (pp. 229-235).
We examined the adsorption of single YOYO-1-labeled λ-DNA molecules at glass surfaces after treatment with various chemical cleaning methods by using total internal reflection fluorescence microscopy (TIRFM). The characteristics of these surfaces were further assessed using contact angle (CA) measurements and atomic force microscopy (AFM). By recording the real-time dynamic motion of DNA molecules at the liquid/solid interface, subtle differences in adsorption affinities were revealed. The results indicate that the driving force for adsorption of DNA molecules on glass surfaces is mainly hydrophobic interaction. We also found that surface topography plays a role in the adsorption dynamics.
Keywords: Single-molecule imaging; Total internal reflection fluorescence microscopy; λ-DNA; Adsorption; Glass surfaces
Surface enhanced Raman scattering from layered assemblies of close-packed gold nanoparticles by Hye Young Jung; Yong-Kyun Park; Sungho Park; Seong Kyu Kim (pp. 236-243).
A synthetic method of ordering hydrophilic gold nanoparticles into a close-packed two-dimensional array at a hexane–water interface and subsequent transferring of such structure onto a solid substrate is described. By repeating the transfer process, multilayered gold nanoparticle films are formed without need of linker molecules. Their surface enhanced Raman scattering (SERS) efficiencies are compared as a function of the number of layers. It is shown that both the number of layers and the particle size contribute to SERS phenomenon. Judging from the noticeable dependence of SERS efficiency on the nanometer scale architecture, the close-packed nanoparticle formation at an immiscible interface presents a facile route to the preparation of highly active and relatively clean SERS substrates by controlling both the particle size and the film thickness. Among the investigated samples, the gold nanoparticle film assembled with quintuple layers of 30nm diameter particles showed the maximum SERS efficiency.
Keywords: Surface enhanced Raman scattering; Enhancement factor; Gold; Au; Nanoparticle; Surface plasmon; Benzenethiol; Thiophenol; Electromagnetic effect; Chemical effect
Cholesterol biosensor based on electrophoretically deposited conducting polymer film derived from nano-structured polyaniline colloidal suspension by Chetna Dhand; S.P. Singh; Sunil K. Arya; Monika Datta; B.D. Malhotra (pp. 244-251).
Cholesterol oxidase (ChOx) has been covalently immobilized onto electrophoretically deposited conducting polymer film (on indium-tin-oxide (ITO) glass plate) derived from nano-structured polyaniline (PANI) colloidal suspension using N-ethyl- N′-(3-dimethylaminopropyl) corbodiimide (EDC) and N-hydroxysuccinimide (NHS) chemistry. These PANI/ITO and ChOx/PANI/ITO electrodes have been characterized using ultraviolet-visible (UV-vis), Fourier transform-infrared (FT-IR), scanning electron microscopy (SEM), and impedance spectroscopy techniques, respectively. These ChOx/PANI/ITO bio-electrodes exhibit linearity from 25 to 400mgdL−1 of cholesterol, detection limit as 25mgdL−1 and sensitivity as 7.76×10−5Abs(mg/dL)−1. The value of the apparent Michaelis–Menten constant (Kmapp) calculated from amperometric response studies has been found to be 0.62mM for ChOx/PANI/ITO bio-electrode.
Keywords: Electrophoretic deposition; Nano-structured polyaniline; Conducting polymer; Cholesterol oxidase; Biosensor
Simultaneous quantification of three isoflavonoid glycosides in rabbit plasma after oral administration of Astragalus mongholicus extract by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry by X. Zhang; Y.G. Sun; M.C. Cheng; Y.Q. Wang; H.B. Xiao; X.M. Liang (pp. 252-258).
A selective and sensitive liquid chromatography coupled with triple stage quadruple tandem mass spectrometry (HPLC/TSQ-MS/MS) was developed and validated for simultaneous quantification of calycosin-7- O-β-d-glycoside (CCSG), formononetin-7- O-β-d-glycoside (Ononin) and ( 6R, 10R)-9,10-dimethoxypterocarpan-3- O-β-d-glycoside (DPG) in rabbit plasma. Plasma samples were extracted with solid-phase extraction (SPE), separated on an Inertsil ODS-3 column and detected by tandem mass spectrometry with electrospray ionization (ESI) interface in positive selective reaction monitoring (SRM) mode. 3,7,8-Trimethoxy-xanthone-1- O-primaverose was used as internal standard (IS) for quantitative measurement. For each analyte, one major product ion was chosen and used for screening of it. Calibration curves were generated over the range of 2–1000ngmL−1 with the correlation coefficients greater than 0.99 by using a weighted (1/ χ) least squares linear regression. The method had the lower limit quantification of 0.15, 0.21 and 0.19 for CCSG, Ononin and DPG, respectively, with precision less than 20%. The intra- and inter-day precisions ranged from 2.48 to 6.38% and 4.81 to 11.78% (R.S.D.%), respectively. This assay is suitable for determining the above three trace glycosides in rabbit plasma simultaneously and thus investigating the pharmacokinetics of glycosides from Astragalus mongholicus extract in rabbits.
Keywords: Isoflavonoid glycoside; Astragalus mongholicus; Liquid chromatography; Tandem mass spectrometry; Plasma