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Analytica Chimica Acta (v.546, #2)
Size sorting of Au and Pt nanoparticles from arbitrary particle size distributions by J. Yang; Jim Yang Lee; Heng-Phon Too (pp. 133-138).
A K2BSPP (dipotassium bis( p-sulfonatophenyl)phenylphosphane dihydrate)-based method to sort and size refine Au and Pt nanoparticles has been developed. It makes use of K2BSPP to impart graduated stability to the nanoparticles in a number of NaCl solutions. The method offers a systematic approach to preparing metal nanoparticles of small diameters and a narrow size distribution from an arbitrary particle size distribution. TEM investigations confirmed the size refinement efficacy of this treatment method: in a typical experiment, the mean particle size and relative standard deviation of Au nanoparticles after three successive treatments were 5.18 and 0.055nm, respectively, down from the corresponding values of 8.22 and 0.26nm from the initial untreated nanoparticle solution. The K2BSPP-based size refinement procedure is a simple alternative to more complex chemical procedures and stringent process control that are currently required for the preparation of mono-dispersed systems.
Keywords: Size sorting; Size refining; K; 2; BSPP; Au nanoparticles
Preparation of poly(vinylpyrrolidone)-protected Prussian blue nanoparticles-modified electrode and its electrocatalytic reduction for hemoglobin by Yuezhong Xian; Yuyan Zhou; Yang Xian; Lihui Zhou; Haiting Wang; Litong Jin (pp. 139-146).
In this paper, a novel modified electrode was developed by using highly dispersed Prussian blue (PB) nanoparticles protected by poly(vinylpyrrolidone) (PVP). The size of the nanoparticles was controlled through adjusting the feed ratio of PVP/Fe2+. Physical characteristics of the nanocomposite were studied by transmission electron microscopy (TEM), UV–vis, IR spectroscopy, and X-ray powder diffraction (XRPD) analysis. The electrocatalytic reduction of hemoglobin (Hb) at PVP-protected PB nanoparticles (PVP/PB NPs)-modified electrode had been investigated. In addition, the size effects and biocompatibility of PVP/PB NPs for the electrochemistry of Hb were also observed. Experimental results indicated that the reduction peak currents of Hb were linear with its concentrations over the range from 1.0×10−7 to 1.2×10−5mol/L and the calculated detection limit ( S/ N=3) was 4.0×10−8mol/L.
Keywords: Prussian blue (PB) nanoparticles; Poly(vinylpyrrolidone) (PVP); Electrochemical catalysis; Hemoglobin (Hb)
Functionalized cadmium sulfide quantum dots as fluorescence probe for silver ion determination by Jin-Long Chen; Chang-Qing Zhu (pp. 147-153).
CdS quantum dots (QDs) modified withl-cysteine has been prepared by one step. They are water-soluble and biocompatible. To improve CdS QDs stability and interaction between silver ion and functionalized CdS QDs in aqueous solution, some amounts of freshl-cysteine were added to functionalized CdS solution. Based on the characteristic fluorescence enhancement of CdS QDs at 545nm by silver ions in the presence of some amounts of freshl-cysteine, simultaneously, a gradual red shift of fluorescence emission bands of CdS QDs from 545 to 558nm was observed. A simple, rapid, sensitive and specific detection method for silver ion was proposed. Under optimum conditions, the fluorescence intensity of CdS QDs is linearly proportional to silver concentration from 2.0×10−8 to 1.0×10−6mol/L with a detection limit of 5.0×10−9mol/L. In comparison with single organic fluorophores, functionalized CdS quantum dots are brighter, more stable against photobleaching, and don’t suffer from blinking. Furthermore, owing to the fluorescence enhancement effect of CdS QDs by silver ion, the proposed method showed lower detection blank and higher sensitivity. Possible fluorescence enhancement mechanism was also studied.
Keywords: CdS quantum dots; Fluorescence; Silver ion
Sequential fluorometric quantification of γ-aminobutyrate andl-glutamate using a single line flow-injection system with immobilized-enzyme reactors by Tadayuki Tsukatani; Kiyoshi Matsumoto (pp. 154-160).
A single line flow-injection system with immobilized-enzyme reactors is proposed for the sequential quantification of γ-aminobutyrate (GABA) andl-glutamate. A co-immobilizedl-glutamate oxidase and catalase reactor and an immobilized GABase reactor were introduced into the flow line in series. Sample and reagent were injected into the flow line using an open sandwich method. GABA was selectively detected by GABase when α-ketoglutarate at a high concentration and NADP+ were injected as the reagents with a sample. When GABA at a high concentration and NADP+ were injected as the reagents with a sample,l-glutamate only was determined by the series of enzymatic reactions. NADPH produced by the immobilized-enzyme reactors was monitored fluorometrically at 455nm (excitation at 340nm). Linear relationships between the responses and concentrations of GABA orl-glutamate were observed in the ranges of 5.0×10−6–5.0×10−4M and 1.0×10−5–5.0×10−4M, respectively. The relative standard deviations for ten successive injections were less than 2% at the 0.5mM level. This analytical method was applied to the sequential quantification of GABA andl-glutamate that were produced and consumed, respectively, by lactic acid bacteria, and the results showed good agreement with those obtained using liquid chromatography.
Keywords: Flow-injection analysis; Immobilized-enzyme reactor; γ-Aminobutyrate; l; -Glutamate; Lactic acid bacteria
Development of colloidal gold-based flow-through and lateral-flow immunoassays for the rapid detection of the insecticide carbaryl by Shuo Wang; Can Zhang; Junping Wang; Yan Zhang (pp. 161-166).
One-step membrane-based competitive colloidal gold-based immunoassays in flow-through and lateral-flow formats for the rapid detection of carbaryl were developed. Nitro-cellulose membrane strip was separately coated with goat anti-rabbit IgG (control line) and carbaryl hapten-OVA conjugate (test line). Anti-carbaryl antibody labeled with colloidal gold particles was firstly incubated with carbaryl. A positive reaction as a result of the remaining antibody-gold conjugate combining with antigen coated on the membrane was obvious by visual detection, with detection limits for flow-through and lateral flow of 50 and l00μg/L, respectively. The assay time for both tests was less than 5min, suitable for rapid testing on-site.
Keywords: Carbaryl; Flow-through; Lateral-flow; Colloidal gold-based immunoassay
Ultra performance liquid chromatography–tandem mass spectrometry for the determination of epirubicin in human plasma by Ruiping Li; Lili Dong; Junxiong Huang (pp. 167-173).
A novel method has been developed for the determination of epirubicin in human plasma by ultra performance liquid chromatography combined with tandem mass spectrometry (UPLC–MS/MS). Epirubicin and internal standard epidaunorubicin were achieved from plasma via solid-phase extraction (SPE) using Oasis HLB cartridge. The analysis was performed on an AcQuity UPLC™ BEH C18 column (1.7μm, 50mm×1mm i.d.) utilizing a gradient elution profile and a mobile phase consisting of 0.1% formic acid in water and acetonitrile. The analytes were detected using an electrospray ionization tandem mass spectrometry in positive ion mode with multiple reaction monitoring (MRM). This method combines both advantages of UPLC and MS/MS, producing superior reliability, sensitivity and accuracy to previously published methods. The calibration curve was linear ( r2=0.998) over the concentration range of 0.50–100.0ng/ml. The limits of detection (LOD) and quantification (LOQ) for epirubicin were 0.10 and 0.50ng/ml using 0.2ml plasma sample, respectively. Recoveries of greater than 89% with intra- and inter-day precision (R.S.D.) less than 12% were obtained at concentrations above the LOQ. The present method has been successfully applied to analyze human plasma samples taken from patients administered epirubicin intravenously. Also, the principal metabolite epirubicinol was detected in all the patient plasma samples under investigation. The proposed method is very rapid, reliable and sensitive, and can be applicable to therapeutical drug monitoring and pharmacokinetic studies of epirubicin.
Keywords: Epirubicin; Biosample analysis; Human plasma; Method validation; UPLC–MS/MS
Simultaneous determination of 17 sulfonamide residues in porcine meat, kidney and liver by solid-phase extraction and liquid chromatography–tandem mass spectrometry by Bing Shao; Dan Dong; Yongning Wu; Jianying Hu; Juan Meng; Xiaoming Tu; Shukun Xu (pp. 174-181).
A precise and reliable method, using normal phase cartridge clean-up and liquid chromatography coupled with tandem mass spectrometry has been developed for measuring the residues of 17 sulfonamides in porcine tissues included in meat, liver and kidney. The parameters of mass spectrometer were optimized by continuous direct injection through a syringe pump. The composition and additives for mobile phases were also evaluated and the optimum one was methanol–water containing 0.1% formic acid. A liquid–liquid extraction and Sep-Pak silica clean-up procedure was developed for sample preparation. The method was validated and found to be satisfactorily linear, selective and robust. Recoveries ranged from 52 to 120% for all compounds at three different spiking levels and the limit of detections (LODs) ranged from 0.01 to 1.0ng/g depending on various compounds.
Keywords: Sulfonamides; LC–MS/MS; Porcine tissues
Collaborative study of an liquid chromatographic method for the determination of R-timolol and other related substances in S-timolol maleate by R.D. Marini; N. Matthijs; Y. Vander Heyden; J. Smeyers-Verbeke; P. Dehouck; J. Hoogmartens; P. Silvestre; A. Ceccato; Ph. Goedert; J. Saevels; C. Herbots; G. Caliaro; R. Herráez-Hernández; J. Verdú-Andrès; P. Campíns-falcó; W. Van de Wauw; J. De Beer; B. Boulanger; P. Chiap; J. Crommen; Ph. Hubert (pp. 182-192).
A collaborative study applying an enantiomeric liquid chromatographic (LC) method was carried out to determine the content of the enantiomeric impurity R-timolol and other related substances in three different S-timolol maleate samples. Eight laboratories, all located in Europe, participated in the study. The quantitative results obtained were used to estimate the uncertainty on the content of the different impurities. For that purpose, a set-up was adapted from the ISO guidelines 5725-2, which allowed the estimation of the different variances, i.e. the between-laboratories (slaboratories2), the between-days (sdays2) and the between-replicates (sreplicates2). The variances of repeatability (sr2) and reproducibility (sR2) were then calculated using the equationssr2=sreplicates2 andsR2=sreplicates2+sdays2+slaboratories2. For the timolol impurities, it was found that the estimated uncertainty seem to be concentration-dependent. Since the LC method which combines the compendial ones for enantiomeric purity and related substances testing was applied to evaluate uncertainty in this collaborative study, it was shown how a laboratory can evaluate the uncertainty of its results when applying the method in the future.
Keywords: Collaborative study; Uncertainty estimation; Reproducibility; R; -timolol; Degradation products; Liquid chromatography
Rapid drug-screening and quantitation of 3,4-methylenedioxymethamphetamine in urine by MALDI-TOF mass spectrometry by An-Kai Su; Ju-Tsung Liu; Cheng-Huang Lin (pp. 193-198).
A method for the rapid screening of the drugs, 3,4-methylenedioxymethamphetamine (MDMA), in urine by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) is described. In this method, α-cyano-4-hydroxycinnamic acid (CHCA) is used as the matrix for the MALDI samples. The identity of MDMA was confirmed by flight time of the fragmentation ([ M+H]+ ion) using a mass calculation curve, the quantification of MDMA was achieved using stable-isotope-labeled MDMA (MDMA-D5) as the internal standard. For the analysis of MDMA/MDMA-D5-spiked urine samples, the calibration curve was linear in the range of 0.1–100ppm with a coefficient of determination, r2, of 0.9993. This assay was used to determine MDMA in actual urine samples. The MALDI-TOFMS results were comparable to the GC/MS results. No significant bias is shown between the two methods by t-test at 95% confidence level. We conclude that MALDI-TOFMS can serve as a reliable and complementary method to GC/MS for use in forensic analysis.
Keywords: 3,4-Methylenedioxymethamphetamine (MDMA); Rapid drug-screening; MALDI-TOF mass spectrometry; α-Cyano-4-hydroxycinnamic acid (CHCA)
Selective anion recognition: Charged diaza crown ethers based electrochemical sensors for chromate ions by L.P. Singh; J.M. Bhatnagar; S. Tanaka; H. Tsue; M. Mori (pp. 199-205).
Attempts have been made to develop a poly(vinyl chloride) (PVC) based sensor for CrO42− ions using positively charged diaza crown ethers (12-crown-4 and 18-crown-6) with dibutylphthalate (DBP), dioctylphthalate (DOP) and chloro naphthalene (CN) and dioctylsebacate (DOS) as plasticizing solvent mediators. These sensors work well over a wide concentration range 5.0×10−6 to 1.0×10−1M (detection limit up to 0.3ppm) with Nernstian slope (29.6mV/decade) between pH 6.5 to 10.0 with a fast response time of <10s. The selectivity coefficient values as determined by Match Potential Method (MPM) indicate excellent selectivity for Cr(VI) ions over a large number of ions. Interference caused by common anions, viz. Cl− and SO42− has been investigated in simulated mixtures containing high concentration level of interfering ions and the sensor was found to be tolerant against these anions. These sensors exhibit adequate shelf-life (>3 months) with good reproducibility (S.D. ±0.2mV). Quantification of Cr(VI) in electroplating waste was successfully achieved using the proposed sensor.
Keywords: Chromium; Sensors; Crown ethers; Chromium-selective electrodes; Chromate ions
Solid phase extraction of amines by C. Molins-Legua; P. Campins-Falcó (pp. 206-220).
The objective of this paper is to provide information about solid phase extraction (SPE) as an alternative to liquid–liquid extraction of amines from several matrices. Different sorbents ranging from non-polar phases, such as C18 silica to more polar such as cyanopropylsilica (CN) have been tested for analysis of aliphatic amines as monoamines, diamines and polyamines. Phenylalkylamines such as amphetamine or methamphetamine and heterocyclic amines such as histamine or cephalosporins (which also contain a carboxylic group), have also been studied. The different steps involved in the extraction procedure have been tested (conditioning, retention, pre-concentration, washing and elution) in order to obtain extracts free of interferences and enough sensitivity. C18 silica (100mg) was selected as optimal phase with recoveries nearly of 100%. The elution of more polar amines was performed in acidic conditions while less polar amines required organic solvents. Cephalosporin retention was performed in acid condition by using disk cartridges EM C18, which gave better selectivity. The optimised clean-up procedures have been discussed to the quantification of the corresponding amines in real samples (urine, water and beer). The accuracy and precision were outlined.
Keywords: Amines; Solid phase extraction; Urine; Water; Beer
Kinetics, thermodynamic and chromatographic behaviour of the uranyl ions sorption from aqueous thiocyanate media onto polyurethane foams by M.S. El-Shahawi; M.A. Othman; M.A. Abdel-Fadeel (pp. 221-228).
The retention profile of uranyl ions from aqueous thiocyanate media by polyether-type based polyurethane foams (PUFs) has been studied to gain more information regarding the mechanism of extraction. The effect of pH, shaking time, surfactant type, extraction media, temperature and analyte concentration on the retention of uranyl ions onto PUFs has been studied. It has been found that, the sorption of uranyl ions involved in the formation of a ternary complex ion associate of uranyl ion, thiocyanate and PUFs is highly dependent on these parameters. The kinetics and thermodynamics of the uranyl ions sorption have been studied in more detail. The dependency of the extraction on the parameters can be explained via a “solvent extraction,� mechanism. However, owing to the complex nature of the PUFs a dual-mode sorption mechanism involving both absorptions related to “solvent extraction� and an added component for “surface adsorption� may be operated simultaneously. Attempts for quantitative retention and recovery of the uranyl ions in tap and industrial waste water samples by the proposed PUFs columns has been carried out and satisfactory results have been obtained. The cellular structure of the PUF sorbent offer unique advantages over a conventional bulk type sorbents in rapid, versatile effective separation and/or preconcentration of uranyl ions.
Keywords: Uranyl ions; PUFs; Sorption; Thiocyanate media; Kinetics and thermodynamics
Vapor phase matrix extraction of high purity di-boron trioxide and trace analysis using electrothermal AAS by K. Dash; S. Thangavel; S.M. Dhavile; S.V. Rao; S.C. Chaurasia; J. Arunachalam (pp. 229-235).
A method has been developed for the determination of Al, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Sb, Sn and Zn at trace levels in high purity di-boron trioxide using ETAAS. The boron trioxide matrix was eliminated as trimethyl borate ester in a multiplex vapor phase matrix extraction (MVPME) device using a mixture of glycerol and methanol. In this MVPME device, in situ reagent purification, sample digestion and simultaneous matrix elimination were achieved by a single step in closed condition, which in combined effect reduce the process blanks. The matrix extraction procedure allows determination of trace elemental impurities by electrothermal atomic absorption spectrometry (ETAAS) with fast furnace analysis (without an ashing step and modifier) and calibration against aqueous standards. The performance and accuracy of the vapor phase matrix elimination technique are compared to those of suprapur grade hydrofluoric acid solution in two ways; (i) matrix separation as BF3 over hot plate and (ii) in situ matrix elimination inside graphite furnaces. The method detection limits calculated from blank samples are in the range of 0.5 (Ni) and 2.9 (Al) ngg−1. Thus the MVPME-based sample preparation approach is well suited for the trace analysis of high purity di-boron trioxide used in microelectronics applications.
Keywords: Di-boron trioxide; Multiplex vapor phase matrix extraction; ETAAS; Trace analysis
An alternative interface for CE–ICP–MS cadmium speciation in metallothioneins based on volatile species generation by G. Álvarez-Llamas; M.R. Fernández de la Campa; A. Sanz-Medel (pp. 236-243).
An alternative CE–ICP–MS interface based on volatile species generation (VSG) is here developed, evaluated and compared to the conventional sample introduction systems via nebulisation. For this purpose, the speciation of Cd–metallothioneins (MTs) in rabbit liver is taken as a model. Cd, bound to the different MT isoforms previously separated by CE, is transformed into volatile species at the exit of the capillary and on-line detected by ICP–MS. Optimum conditions for Cd VSG have been investigated in a flow injection device, using NaBH4 as hydrogenation reagent in a HCl medium containing cobalt and thiourea as catalysts. Sample volume injected, CE separation voltage and reagents flows have been optimised. Analytical performance characteristics of the CE–VSG–ICP–(Q)MS coupling developed were evaluated, in terms of repeatability and linearity of response, using standard rabbit liver metallothionein isoforms (MT1 and MT2). Detection limits for Cd–MTs turned out to be almost one order of magnitude better than those derived from using a conventional Babington nebuliser-based interface. Compared to a MicroMist-based interface detection limits resulted to be similar, but the observed peak height was eight times higher using the VSG interface, indicating the enhanced analyte transport efficiency derived from VSG sample introduction systems.
Keywords: CE; ICP–MS; Cadmium; Metallothioneins; Vapour generation
On-line preconcentration and speciation analysis of Cr(III) and Cr(VI) using baker's yeast cells immobilised on controlled pore glass by Amauri A. Menegário; Patricia Smichowski; Griselda Polla (pp. 244-250).
A study was undertaken to evaluate Saccharomyces cerevisiae as a substrate for the biosorption of Cr(III) and Cr(VI) aiming to the selective determination of these species in aqueous solutions. The yeast cells were covalently immobilised on controlled pore glass (CPG), packed in a minicolumn and incorporated in an on-line flow injection system. The effect of chemical and physical variables affecting the biosorption process was tested in order to select the optimal analytical conditions for the Cr retention by S. cerevisiae. Cr(III) was retained by the immobilised cells and Cr(VI) were retained by CPG. The speciation was possible by selective and sequential elution of Cr(III) with 0.05molL−1 HCl and 2.0molL−1 HNO3 for Cr(VI). The influence of some concomitant ions up to 20mgL−1 was also tested. Quantitative determinations of Cr were carried out by means of inductively coupled plasma optical emission spectrometry (ICP OES). Preconcentration factors of 12 were achieved for Cr(III) and 5 for Cr(VI) when 1.7mL of sample were processed reaching detection limits of 0.45 for Cr(III) and 1.5μgL−1 for Cr(VI). The speciation of inorganic Cr in different kinds of natural waters was performed following the proposed method. Spiked water samples were also analysed and the recoveries were in all cases between 81 and 103%.
Keywords: Cr(III); Cr(VI); Saccharomyces cerevisiae; Immobilisation; Controlled pore glass; Preconcentration; Speciation analysis