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Analytica Chimica Acta (v.668, #2)

Editorial Board (pp. i).

Molecularly imprinted polymers for sample preparation: A review by Esther Turiel; Antonio Martín-Esteban (pp. 87-99).

In spite of the huge development of analytical instrumentation during last two decades, sample preparation is still nowadays considered the bottleneck of the whole analytical process. In this regard, efforts have been conducted towards the improvement of the selectivity during extraction and/or subsequent clean-up of sample extracts. Molecularly imprinted polymers (MIPs) are stable polymers with molecular recognition abilities, provided by the presence of a template during their synthesis and thus are excellent materials to provide selectivity to sample preparation. In the present review, the use of MIPs in solid-phase extraction and solid-phase microextraction as well as its recent incorporation to other extraction techniques such as matrix-solid phase dispersion and stir bar sorptive extraction, among others, is described. The advantages and drawbacks of each methodology as well as the future expected trends are discussed.

Keywords: Molecular imprinting; Sample preparation; Solid-phase extraction; Solid-phase microextraction; Review

Review on recent and advanced applications of monoliths and related porous polymer gels in micro-fluidic devices by Mercedes Vázquez; Brett Paull (pp. 100-113).

This review critically summarises recent novel and advanced achievements in the application of monolithic materials and related porous polymer gels in micro-fluidic devices appearing within the literature over the period of the last 5 years (2005–2010). The range of monolithic materials has developed rapidly over the past decade, with a diverse and highly versatile class of materials now available, with each exhibiting distinct porosities, pore sizes, and a wide variety of surface functionalities. A major advantage of these materials is their ease of preparation in micro-fluidic channels by in situ polymerisation, leading to monolithic materials being increasingly utilised for a larger variety of purposes in micro-fluidic platforms. Applications of porous polymer monoliths, silica-based monoliths and related homogeneous porous polymer gels in the preparation of separation columns, ion-permeable membranes, preconcentrators, extractors, electrospray emitters, micro-valves, electrokinetic pumps, micro-reactors and micro-mixers in micro-fluidic devices are discussed herein. Procedures used in the preparation of monolithic materials in micro-channels, as well as some practical aspects of the micro-fluidic chip fabrication are addressed. Recent analytical/bioanalytical and catalytic applications of the final micro-fluidic devices incorporating monolithic materials are also reviewed.

Keywords: Abbreviations; AAm; acrylamide; AChE; acetylcholinesterase; AIBN; 2,2′-azobis(isobutyronitrile); AMPS; 2-acrylamide-2-methyl-propanesulfonic acid; APS; ammonium persulfate; BDDA; 1,3-butanediol diacrylate; BMA; butyl methacrylate; BVPE; bis-vinylphenyl ethane; CHO; choline oxidase; COC; cyclic olefin copolymer; DMPA; 2,2′-dimethoxy-2-phenylacetophenone; DVB; divinylbenzene; EDA; ethylene diacrylate; EDMA; ethylene dimethacrylate; EGDMA; ethylene glycol dimethacrylate; EHMA; ethylhexyl methacrylate; EFGF; electric field gradient focusing; ELISA; enzyme-linked immunosorbent assay; EOF; electroosmotic flow; EOPs; electroosmotic pumps; ESI; electrospray ionisation; ESI-MS; electrospray ionisation mass spectrometry; FFIEF; free-flow isoelectric focusing; FITC; fluorescein isothiocyanate; GFP; green fluorescent protein; GMA; glycidyl methacrylate; HA; hexyl acrylate; HEMA; hydroxylethyl methacrylate; HSA; human serum albumin; IgG; immunoglobulin G; ILs; ionic liquids; IEF; isoelectric focusing; LA; lauryl acrylate; LED; light emitting diode; LCST; lower critical solution temperature; LIF; laser induced fluorescence; LIGA; lithography, electroplating and moulding; LMA; lauryl methacrylate; LTCC; low temperature co-fired ceramic technology; MBAA; N; ,; N; ′-methylenebis(acrylamide); MMA; methyl methacrylate; MS; 4-methylstyrene; MTMOS; methyl trimethoxysilane; NHS; N; -hydroxysuccinimide; NIPAAm; N; -isopropylacrylamide; ODS; octadecyl silica; PAHs; polycyclic aromatic hydrocarbons; PBS; phosphate buffer saline solution; PC; polycarbonate; PCR; polymerase chain reaction; PDMS; polydimethylsiloxane; PEG; poly(ethylene glycol); PEI; polyethylenimine; p; I; isoelectric point; PMMA; poly(methyl methacrylate); PTMOS; phenethyl trimethoxysilane; TEGDMA; tetraethylene glycol dimethacrylate; TEMED; N; ,; N; ,; N; ′,; N; ′-tetramethylethylenediamine; TEOS; tetraethoxysilane; THF; tetrahydrofuran; TMOS; tetramethoxysilane; TMPTMA; trimethylolpropane trimethacrylate; TMSPM; 3-(trimethoxysilyl)propyl methacrylate; SDS-PAGE; sodium dodecyl sulfate polyacrylamide gel electrophoresis; SP; spirobenzopyran; ST; styrene; Sulfo-SMCC; sulfosuccinimidyl-4-(; N; -maleimidomethyl)cyclohexane-1-carboxylate; μEC; micro-electro-chromatography; μFIA; micro-flow injection analysis; μLC; micro-liquid chromatography; μSPE; micro-solid phase extractionMicro-fluidic platforms; Monoliths; On-chip extraction; On-chip preconcentration; Micro-valves; Micro-mixers; Micro-reactors; Ion-permeable membranes

Environmental application of elemental speciation analysis based on liquid or gas chromatography hyphenated to inductively coupled plasma mass spectrometry—A review by Maximilian Popp; Stephan Hann; Gunda Koellensperger (pp. 114-129).

In recent years the number of environmental applications of elemental speciation analysis using inductively coupled plasma mass spectrometry (ICP-MS) as detector has increased significantly. The analytical characteristics, such as extremely low detection limits (LOD) for almost all elements, the wide linear range, the possibility for multi-elemental analysis and the possibility to apply isotope dilution mass spectrometry (IDMS) make ICP-MS an attractive tool for elemental speciation analysis. Two methodological approaches, i.e. the combination of ICP-MS with high performance liquid chromatography (HPLC) and gas chromatography (GC), dominate the field. Besides the investigation of metals and metalloids and their species (e.g. Sn, Hg, As), representing “classic” elements in environmental science, more recently other elements (e.g. P, S, Br, I) amenable to ICP-MS determination were addressed. In addition, the introduction of isotope dilution analysis and the development of isotopically labeled species-specific standards have contributed to the success of ICP-MS in the field. The aim of this review is to summarize these developments and to highlight recent trends in the environmental application of ICP-MS coupled to GC and HPLC.

Keywords: Abbreviations; AB; arsenobetaine; AC; arsenocholine; AEC; anion exchange chromatography; AMPA; aminomethylphosphonic acid; As(III); arsenite; As(V); arsenate; BFR; brominated flame retardants; CCA; chromated copper arsenate; CE; capillary electrophoresis; CEC; cation exchange chromatography; CPC; cancerostatic platinum compound; CRM; certified reference material; CV; cold vapor generation; DBT; dibutyltin; DEL; diethyllead; DGT; diffusive gradient in thin film; DIHEN; direct insertion high efficiency nebulizer; DMA; dimethlylarsinate; DMAA; dimethylarsinoylacetate; DML; dimethyllead; DMT; dimethyltin; DPhA; diphenylarsinic acid; DPhT; diphenyltin; DRC; dynamic reaction cell; EI-MS; electron ionisation mass spectrometry; EMPA; ethyl methylphosphonic acid; EPA; environmental protection agency; ESI-MS; electrospray ionisation mass spectrometry; ESR; electron spin resonance; EtHg; ⁺; ethyl-mercury; GC; gas chromatography; GC-ICP-MS; gas chromatography inductively coupled plasma spectrometry; GC-ICP-TOF-MS; gas chromatography inductively coupled plasma time of flight mass spectrometry; HF-LPME; hollow fiber-liquid phase micro-extraction; HG-PT-GC-ICP-MS; purge and trap gas chromatography coupled to ICP-MS; HILIC; hydrophilic interaction chromatography; HPIC; high performance ion chromatography; HPLC; high performance liquid chromatography; HPLC-ICP-MS; high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry; HS-SDME; head space single drop microextraction; HS-SPME; head space solid phase microextraction; IC; ion chromatography; IC-ICP-MS; ion chromatography inductively coupled plasma mass spectrometry; IC-ICP-QMS; ion chromatography coupled to ICP-QMS; IC-ICP-SFMS; ion chromatography coupled to ICP-SFMS; ICP; inductively coupled plasma; ICP-AES; inductively coupled plasma atomic emission spectrometry; ICP-DRC-MS; ICP-MS equipped with a dynamic reaction cell; ICP-MS; inductively coupled plasma mass spectrometry; ICP-QMS; inductively coupled plasma quadrupole mass spectrometry; ICP-SFMS; inductively coupled plasma sector-field mass spectrometry; ICP-TOF-MS; inductively coupled plasma time of flight mass spectrometry; ID; isotope dilution; ID-GC-ICP-MS; isotope dilution gas chromatography inductively coupled plasma mass spectrometry; IDMS; isotope dilution mass spectrometry; IMPA; isopropyl methylphosphonic acid; IT-MS; ion trap mass spectrometry; LC; liquid chromatography; LC-ICP-MS; liquid chromatography inductively coupled plasma mass spectrometry; LLE; liquid liquid extraction; LOD; limit of detection; MBT; monobutyltin; MCN; microconcentric nebulizer; Me; ₂; Hg; dimethyl-mercury; MeHg; ⁺; methylmercury; MIP-AES; microwave induced plasma atomic emission spectrometry; MMA; monomethylarsonate; MMT; monomethyltin; MPA; methylphosphonic acid; MPhT; monophenyltin; MRI; magnetic resonance imaging; NaBEt; ₄; sodium tetraethylborate; NaBPr; ₄; sodium tetrapropylborate; p-ASA; p-arsanilic acid; PBDPE; polybrominated diphenyl ether; PhA; phenylarsonic acid; PhAO; phenylarsine oxide; PhHg+; phenylmercury; ppb; parts per billion; ppt; parts per trillion; PT; purge and trap; PTI; purge and trap injection; QMS; quadrupole mass spectrometry; RF; radio frequency; RP; reversed phase; RP-HPLC; reversed phase high performance liquid chromatography; RP-HPLC-ICP-DRC-MS; high performance liquid chromatography coupled to inductively coupled plasma dynamic reaction cell mass spectrometry; RSD; relative standard deviation; SEC; size exclusion chromatography; SFMS; (double-focusing) sector field mass spectrometry; SPE; solid phase extraction; SPME; solid phase microextraction; SS; species specific; SU; species unspecific; TBT; tributyltin; TEL; triethyllead; TeMA; tetramethylarsonium; THM; trihalomethanes; TMAO; trimethylarsine oxide; TML; trimethyllead; TMSbCl; ₂; trimethylantimony dichloride; TMT; trimethyltin; TOF-MS; time of flight mass spectrometry; TPhT; triphenyltin; USN; ultrasonic nebulizerElemental speciation analysis; Environmental analysis; LC-ICP-MS; GC-ICP-MS

Improvement of Direct Calibration in spectroscopy by Jean-Claude Boulet; Jean-Michel Roger (pp. 130-136).

Several linear calibration methods have been proposed for predicting the concentration of a particular compound from a spectrum. Some methods are based on experimental data, such as Partial Least Square Regression. Other methods are based on expert data, e.g. Direct Calibration. This article proposes a new method, called Improved Direct Calibration, which uses expert and experimental information. It performs a projection onto the pure interest spectrum, after correcting it from influence factors. No calibration dataset is necessary to build this model. This method has been successfully applied to the quantification of ethanol in musts during fermentation, using near infrared spectrometry.

Keywords: Linear; Direct; Calibration; Multivariate; Prediction; Spectrometry; Analysis

Determination of an acceptable level of spectral data compression by Discrete Wavelet Transforms by Mohsen Kompany-Zareh; Frans van den Berg (pp. 137-142).

Today, due to the ever increasing amount of data generated by analytical instruments, good compression methods are desired to keep computation time acceptable. The lower the volume and noise content of data, the easier it becomes to investigate and interpret the modeling results. Discrete Wavelet Transform (DWT) is an effective data compression and noise suppression tool. Compression can be performed at different levels, in each, the size of signal part of the data reduces to half the size. This work includes an approach for determining an acceptable level of compression of data where the aim is to achieve minimal loss of information and no significant change in the structure of data, which could mean, e.g. no loss in predictive ability or the effective rank of the data-set. The method is based on estimation of the Singular Values (SVs) from a data matrix and the Singular Values at each level of compression followed by the application of Median Absolute Deviation (MAD) of the correlation between original SVs and compression SVs as a simple statistical test for the determination of the optimum level of compression. We illustrate the method using FT-Raman data from aqueous solutions of three sugars (glucose, trehalose and sucrose) and NMR data from mixtures of three alcohols. A sudden change in prediction error sum of square plots from Partial Least Squares (PLS) modeling confirms the results from MAD statistics.

Keywords: Discrete Wavelet Transform; Median Absolute Deviation; Data compression; Noise reduction

NIR and UV–vis spectroscopy, artificial nose and tongue: Comparison of four fingerprinting techniques for the characterisation of Italian red wines by M. Casale; P. Oliveri; C. Armanino; S. Lanteri; M. Forina (pp. 143-148).

Four rapid and low-cost vanguard analytical systems (NIR and UV–vis spectroscopy, a headspace-mass based artificial nose and a voltammetric artificial tongue), together with chemometric pattern recognition techniques, were applied and compared in addressing a food authentication problem: the distinction between wine samples from the same Italian oenological region, according to the grape variety.Specifically, 59 certified samples belonging to the Barbera d’Alba and Dolcetto d’Alba appellations and collected from the same vintage (2007) were analysed.The instrumental responses, after proper data pre-processing, were used as fingerprints of the characteristics of the samples: the results from principal component analysis and linear discriminant analysis were discussed, comparing the capability of the four analytical strategies in addressing the problem studied.

Keywords: NIR spectroscopy; UV–vis spectroscopy; Artificial nose; Artificial tongue; Wine; Chemometrics

A novel storage method for near infrared spectroscopy chemometric models by Zhi-Min Zhang; Shan Chen; Yi-Zeng Liang (pp. 149-154).

Chemometric Modeling Markup Language (CMML) is developed by us for containing chemometrics models within one document through converting binary data into strings by base64 encode/decode algorithms to solve the interoperability issue in sharing chemometrics models. It provides a base functionality for storage of sampling, variable selection, pretreating, outlier and modeling parameters and data. With the help of base64 algorithm, the usability of CMML is in equilibrium with size by transforming the binary data into base64 encoded string. Due to the advantages of Extensible Markup Language (XML), models stored in CMML can be easily reused in various other software and programming languages as long as the programming language has XML parsing library. One can also use the XML Path Language (XPath) query language to select desired data from the CMML file effectively. The application of this language in near infrared spectroscopy model storage is implemented as a class in C++ language and available as open source software (http://code.google.com/p/cmml), and the implementations in other languages, such as MATLAB and R are in progress.

Keywords: Chemometrics; Modeling; Extensible Markup Language; Model storage; Near infrared spectroscopy; Raman

The use of cyclic voltammetry for wine analysis: Determination of polyphenols and free sulfur dioxide by Olga Makhotkina; Paul A. Kilmartin (pp. 155-165).

The use of cyclic voltammetry to characterize wines and wine polyphenols in a pH 3.3 model wine solution has been extended to take into account the effects of sulfur dioxide and polyphenol adsorption processes. A good correlation was obtained between a cyclic voltammetric measure, based upon the response produced before and after acetaldehyde additions, and the concentration of free sulfur dioxide in eight white wines ( r²=0.974). By the addition of acetaldehyde to the white wines, an important new step in the methodology, the area under the anodic scan in the potential range from −100 to 1200mV (Ag/AgCl) closely matched the spectroscopic measure of total polyphenols (absorbance at 280nm) for the white wines, when both were measured in terms of caffeic acid equivalents ( r²=0.949). The anodic peak area accounted for about 70% of the 280nm total phenols measure, in catechin equivalents, for the red wines, and a good linear correlation was also obtained ( r²=0.942). The level of catechol and galloyl-containing polyphenols in the wines was calculated by measuring the size of the first anodic peak at around 450mV after treatment of the wines with acetaldehyde; the peak current correlated well with the total caffeic acid derivatives in the white wines determined by HPLC ( r²=0.982). The concentration of flavonols was estimated by selective adsorption of these compounds onto the carbon electrode and determining the anodic peak current at 1120mV, with good correlations obtained when compared to total flavonols as measured by HPLC ( r²=0.984 for the red wines, and r²=0.987 for the white wines).

Keywords: Cyclic voltammetry; Wine; Phenolics; Adsorption; Sulfur dioxide; Total polyphenols

A label-free electrochemical test for DNA-binding activities of tumor suppressor protein p53 using immunoprecipitation at magnetic beads by Kateřina Němcová; Luděk Havran; Peter Šebest; Marie Brázdová; Hana Pivoňková; Miroslav Fojta (pp. 166-170).

In this paper we extend the application area of the label-free structure-sensitive electrochemical DNA sensing with mercury-based electrodes which is for the first time used, in combination with immunoprecipitation at magnetic beads (MB), for the probing of DNA interactions with tumor suppressor protein p53. The technique relies on capture of the p53–DNA complexes at MB via anti-p53 antibodies, followed by salt-induced dissociation of linear DNA from the complex and its voltammetric detection. Competitive binding of p53 to various plasmid DNA substrates, including lin or scDNAs with or without a specific target site, can easily be followed by ex situ electrochemical analysis of DNA recovered from the immunoprecipitated complexes. Compared to gel electrophoresis which is usually applied to analyze different plasmid DNA forms and their complexes with proteins, the electrochemical detection is faster and allows simpler quantitation of DNA containing free ends at submicrogram levels. We demonstrate applicability of the proposed technique to monitor different DNA-binding activities of wild type and mutant p53 proteins.

Keywords: Electrochemical analysis; Label-free detection; Tumor suppressor protein p53; DNA–protein interaction; Immunoprecipitation; Magnetic beads

A novel label-free electrochemical aptasensor for thrombin based on the {nano-Au/thionine}_n multilayer films as redox probes by Yali Yuan; Ruo Yuan; Yaqin Chai; Ying Zhuo; Zhongyuan Liu; Li Mao; Shu Guan; Xiaoqing Qian (pp. 171-176).

Herein, a novel label-free electrochemical aptasensor based on direct immobilization of the redox probes on an electrode surface was reported. Gold electrode coated Nafion was firstly modified with redox probe-thionine (Thi) through ion exchange adsorption. Then, with the help of chemisorption and electrostatic adsorption, negatively charged nano-Au and positively charged Thi were layer-by-layer (LBL) self-assembled onto the modified electrode surface, which formed {nano-Au/Thi⁺}_n multilayer films for improving the amount of redox probes and immobilizing thiolated thrombin aptamers (TBA). In the presence of target thrombin (TB), the TBA on the multilayer film could catch the TB onto the electrode surface, which resulted in a barrier for electro-transfer, leading to decrease of the current. The proposed method avoided the cubsome redox probe labeling process, increased the amount of redox probe and reduced the distance between the redox probe and electrode surface. Thus, the approach showed a high sensitivity and a wider linearity to TB in the range from 0.12nM to 46nM with a detection limit of 40pM.

Keywords: Aptamer; Thrombin (TB); Redox probe; Electrochemical aptasensor

Determination of Pb²⁺ in natural waters with 2-mercaptobenzimidazole-5-sulfonate (MBIS)chemically modified gold electrode by Francesca Zavarise; Daniele Merli; Antonella Profumo (pp. 177-181).

The preparation, characterization and analytical applications of gold electrodes modified with ω-mercapto alkyl/aryl sulfonates are described. The devices resulted effective for the determination of free and labile Pb(II) in water samples by anodic stripping voltammetry ( E_dep=−600mV) and in particular 2-mercaptobenzimidazole-5-sulfonate (MBIS) offered the best performances with detection limit of 0.4μgL⁻¹.Quantitative stripping of Pb from the electrode surface during the anodic scan, is obtained using sodium citrate buffer (pH=9.0) as supporting electrolyte. Natural waters were analysed by standard addition method with good recoveries (mean percentage=97%); no fouling effects due to humic acids or other organic constituents were observed in the reported conditions.

Keywords: Chemically modified electrodes (CME); Pb determination; Mercaptoethane sulfonate (MES); 3-Mercaptopropane sulfonate (MPS); 2-Mercaptobenzimidazole-5-sulfonate (MBIS); Electrochemical sensors

Electrodeposited nano-scale islands of ruthenium oxide as a bifunctional electrocatalyst for simultaneous catalytic oxidation of hydrazine and hydroxylamine by Hamid R. Zare; S. Hossein Hashemi; Ali Benvidi (pp. 182-187).

For the first time, an electrodeposited nano-scale islands of ruthenium oxide (ruthenium oxide nanoparticles), as an excellent bifunctional electrocatalyst, was successfully used for hydrazine and hydroxylamine electrocatalytic oxidation. The results show that, at the present bifunctional modified electrode, two different redox couples of ruthenium oxides serve as electrocatalysts for simultaneous electrocatalytic oxidation of hydrazine and hydroxylamine. At the modified electrode surface, the peaks of differential pulse voltammetry (DPV) for hydrazine and hydroxylamine oxidation were clearly separated from each other when they co-exited in solution. Thus, it was possible to simultaneously determine hydrazine and hydroxylamine in the samples at a ruthenium oxide nanoparticles modified glassy carbon electrode (RuON-GCE). Linear calibration curves were obtained for 2.0–268.3μM and 268.3–417.3μM of hydrazine and for 4.0–33.8μM and 33.8–78.3μM of hydroxylamine at the modified electrode surface using an amperometric method. The amperometric method also exhibited the detection limits of 0.15μM and 0.45μM for hydrazine and hydroxylamine respectively. RuON-GCE was satisfactorily used for determination of spiked hydrazine in two water samples. Moreover, the studied bifunctional modified electrode exhibited high sensitivity, good repeatability, wide linear range and long-term stability.

Keywords: Hydrazine; Hydroxylamine; Bifunctional modified electrode; Ruthenium oxide nanoparticles; Simultaneous determination

Determination of additives in cosmetics by supercritical fluid extraction on-line headspace solid-phase microextraction combined with gas chromatography–mass spectrometry by Tzung-Jie Yang; Feng-Jie Tsai; Chung-Yu Chen; Thomas Ching-Cherng Yang; Maw-Rong Lee (pp. 188-194).

A new hyphenated technique couples supercritical fluid extraction in situ derivatization and on-line headspace solid-phase microextraction to gas chromatography–mass spectrometry (SFE in situ derivatization on-line HS–SPME–GC–MS) for the determination of paraben preservatives and polyphenolic antioxidants in cosmetics. The preservatives and antioxidants were extracted from the cosmetic matrices with supercritical carbon dioxide at a pressure of 13,840kPa. The supercritical fluid extraction was performed at 55°C for 10min of static extraction then 15min of dynamic extraction. The extractant subsequently was derivatized in situ with the silylation reagent N, O-bis(trimethylsilyl)trifluoroacetamide with 0.1% trimethylchlorosilane. The product was then adsorbed on a polyacrylate solid-phase microextraction (SPME) fiber in the headspace. Sea sand was used as a dispersive material in the SFE step. The analytical linear ranges for the preservatives and antioxidants were found to be from 10 to 1000ngg⁻¹ with RSD values below 7.8%. The detection limits ranged from 0.5 to 8.3ngg⁻¹. These results are better than those obtained by using only SPME or SFE for trace preservatives and antioxidants analysis in cosmetic matrices. The new method was successfully utilized to determine the amounts of preservatives and antioxidants in real cosmetics without the need for tedious pretreatments.

Keywords: Supercritical fluid extraction on-line with solid-phase microextraction; Cosmetics; Preservatives; Antioxidants

Griess micro-assay for the determination of nitrite by combining fibre optics-based cuvetteless UV–Vis micro-spectrophotometry with liquid-phase microextraction by Sonia Senra-Ferreiro; Francisco Pena-Pereira; Isela Lavilla; Carlos Bendicho (pp. 195-200).

A novel, simple and low cost method for the determination of nitrite using headspace single-drop microextraction and cuvetteless ultraviolet–visible micro-spectrophotometry is described. A Griess reagent-containing aqueous microdrop exposed to the headspace was used as extractant of the volatile nitrogen oxides generated from nitrite by direct acidification of the aqueous sample. Experimental parameters affecting the headspace single-drop microextraction performance such as composition and volume of the extractant phase, sample volume, concentration of acetic acid, ionic strength, sample agitation, temperature and microextraction time were systematically examined. Measurements were carried out at 540nm under optimized conditions. A detection limit of 1.5μgL⁻¹ and an enrichment factor of 193 were achieved. Intra-day repeatability and inter-day reproducibility, expressed as relative standard deviation, were 3.5% ( n=7) and 10.6% (three consecutive days), respectively. The proposed method, characterized by its enhanced sensitivity and selectivity in comparison with the standardized colorimetric assay, was successfully applied to the analysis of several environmental water samples.

Keywords: Griess micro-assay; Single-drop microextraction; Fibre optics-based cuvetteless ultraviolet–visible micro-spectrophotometry; Nitrite determination; Waters

Carbon and diamond paste microelectrodes based on Mn(III) porphyrins for the determination of dopamine by Simona Cornelia Balasoiu; Raluca-Ioana Stefan-van Staden; Jacobus Frederick van Staden; Stela Pruneanu; Gabriel-Lucian Radu (pp. 201-207).

Three Mn(III) porphyrins were used for the design of carbon paste and diamond paste based microelectrodes, which were employed for the determination of dopamine in pharmaceutical and biological samples using differential pulse voltammetry (DPV). The limits of detection lie between 1.6×10⁻¹³ and 2.0×10⁻⁶molL⁻¹ while the sensitivities were between 230pAμmolL⁻¹ and 3.24μAmolL⁻¹. Dopamine was recovered reliable from pharmaceutical and biological samples in percentages higher than 91.00% and 92.00%, respectively. The surface of the microelectrodes can easily be renewed by simple polishing, obtaining a fresh surface ready for use in a new assay.

Keywords: Mn(III) porphyrin; Dopamine; Carbon paste; Diamond paste; Microelectrode

Monitoring human telomere DNA hybridization and G-quadruplex formation using gold nanorods by Xin-Chun Gou; Jun Liu; Hao-Li Zhang (pp. 208-214).

A facile and multi-response strategy for studying the transformations of human telomere DNA from single strand (ss) to double strand (ds) and G-quadruplex has been established by using positively charged gold nanorod (AuNR) as an optical label. The conformation change information of the telomere DNA was transferred into multiple optical signals, including changes in fluorescence emission, near infrared (NIR) absorption, plasma resonance light scattering (PRLS) and dynamic light scattering (DLS) response. The formations of dsDNA and G-quadruplex DNA induced fluorescence quenching of dye on DNA, and were accompanied by the intensity decrease and blue shift of the longitudinal absorption peak of AuNRs. Meanwhile, PRLS and DLS results revealed slightly increased AuNR aggregation due to increased charge density of dsDNA and G-quadruplex DNA as compared to ssDNA. Control experiment suggests that the AuNR-based assay is highly sequence specific; and the high sensitivity allows the study of human telomere DNA at a concentration as low as 58nM.

Keywords: Biosensor; Telomere DNA; G-quadruplex; Gold nanorods (AuNRs)

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Analytica Chimica Acta (v.668, #2)