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Relative Standard Deviation (relative + standard_deviation)
Selected AbstractsImproved workup for glycosaminoglycan disaccharide analysis using CE with LIF detectionELECTROPHORESIS, Issue 22 2008Alicia M. Hitchcock Abstract This work describes improved workup and instrumental conditions to enable robust, sensitive glycosaminoglycan (GAG) disaccharide analysis from complex biological samples. In the process of applying CE with LIF to GAG disaccharide analysis in biological samples, we have made improvements to existing methods. These include (i) optimization of reductive amination conditions, (ii) improvement in sensitivity through the use of a cellulose cleanup procedure for the derivatization, and (iii) optimization of separation conditions for robustness and reproducibility. The improved method enables analysis of disaccharide quantities as low as 1,pmol prior to derivatization. Biological GAG samples were exhaustively digested using lyase enzymes, the disaccharide products and standards were derivatized with the fluorophore 2-aminoacridone and subjected to reversed polarity CE-LIF detection. These conditions resolved all known chondroitin sulfate (CS) disaccharides or 11 of 12 standard heparin/heparan sulfate disaccharides, using 50,mM phosphate buffer, pH 3.5, and reversed polarity at 30,kV with 0.3,psi pressure. Relative standard deviation in migration times of CS ranged from 0.1 to 2.0% over 60 days, and the relative standard deviations of peak areas were less than 3.2%, suggesting that the method is reproducible and precise. The CS disaccharide compositions are similar to those obtained by our group using tandem MS. The reversed polarity CE-LIF disaccharide analysis protocol yields baseline resolution and quantification of heparin/heparan sulfate and CS/dermatan sulfate disaccharides from both standard preparations and biologically relevant proteoglycan samples. The improved CE-LIF method enables disaccharide quantification of biologically relevant proteoglycans from small samples of intact tissue. [source] Direct Current Plasma Emission Spectrometric Determination of Major, Minor and Trace Elements in Microwave Oven Acid Leachates of Powdered Whole Coal SamplesGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 1 2005Sandro Fadda DCP-AES; échantillons de charbon; four à micro-ondes; éléments facilement ionisables; effets de matrice. Major concentrations of Al2O3, Fe2O3, MgO, CaO, Na2O and K2O, minor levels of TiO2, P2O5 and thirty petrologically, geochemically and environmentally significant trace elements have been determined in microwave oven acid leachates of whole powdered coal samples by direct current plasma-atomic emission spectrometry (DCP-AES). A single sample preparation procedure was suitable for all the determinations with no additional dilution step for major elements solution. Dried samples (0.5 g) were treated in low-pressure PFA digestion vessels with HF/HCl/HNO3/HClO4 acids to quantitatively extract the analytes from the bulk material, while leaving the major part of organic matrix as a residue. The major constituents of geological samples, in particular the easily ionised elements (EIEs) such as alkali and alkaline earths, may complicate the instrumental determinations in DCP-AES because of differential enhancements of elemental emission intensities and stray light interferences. Taking account of these factors, the coal matrix is considered to have very low major oxide totals as compared to many other common geo-environmental and related materials (rocks, sediments, soil, ashes etc.). The sample size employed here, while yielding a relatively concentrated solution to cover a wide range of elemental determinations, provided a sample matrix that significantly diminished interferences for DCP measurements. The need for closely matching the unknowns and calibrators was eliminated except for overall acidity and an excess quantity of caesium for EIE buffering. Calibration of the spectrometer was accomplished by simple aqueous single element solutions as high concentration calibrators in addition to a reagent blank as a low concentration calibrator. Two point working curves were established to allow for the maximum concentrations of each element expected in the unknowns. The precision of determinations under routine conditions as well as the reproducibility of the leaching and precision of instrumental measurements have been evaluated. Relative standard deviations (RSD) were of 1,2% for those elements whose concentrations in solid samples were well above the limits of quantification. Method detection limits in the buffered solutions were also evaluated. To evaluate the accuracy of the microwave oven-DCP method a suite of eight certified coal reference materials of differing rank, were analysed with good agreement with the certified and/or available published data. Results are presented for the uncertified major oxides in the AR series reference materials. Les concentrations en éléments majeurs: Al2O3, Fe2O3, MgO, CaO, Na2O et K2O, en éléments mineurs TiO2, P2O5 et en 30 éléments en trace dont le comportement est important en Pétrologie, en Géochimie et en Environnement, ont été analysées par spectrométrie d'émission atomique à plasma à courant direct (DCP-AES), dans des lessivages acides effectués dans un four à micro-ondes sur des échantillons de charbon mis en poudre. Ce mode préparatoire unique est adaptéà toutes les déterminations sans qu'il soit nécessaire d'effectuer une dilution supplémentaire pour l'analyse des éléments majeurs. Les échantillons préalablement desséchés (0.5 g) sont traités dans les pots de PFA de basse pression, avec un mélange d'acides HF/HCl/HNO3/HClO4, afin d'extraire quantitativement les analytes du matériel géologique, tout en laissant la plus grande part de la matrice organique sous forme résiduelle. Les constituants majeurs de ces échantillons géologiques, en particulier les éléments facilement ionisables (EIEs) tels que les alcalins et les alcalino-terreux, peuvent compliquer l'analyse en DCP-AES à cause des rendements variables des intensités d'émission élémentaires et des interférences de raies de lumière. Mais là dessus, la matrice de charbon se révèle être bien plus pauvre en oxydes majeurs que les autres matériaux géologiques, environnementaux ou de type proche (roches, sédiments, sols, cendres). La taille d'échantillon retenue ici, tout en fournissant une solution relativement concentrée qui permet la détermination de beaucoup d'éléments, fournit une matrice qui diminue significativement les interférences lors de la mesure par DCP-AES. Le besoin d'avoir les solutions d'échantillons et les solutions de calibration avec des matrices très proches est donc éliminé, mis à part pour l'acidité totale et la quantité excessive de Césium pour tamponner les EIE. La calibration du spectromètre est faite avec des solutions mono- élémentaires aqueuses, pour déterminer les points de concentrations élevées et avec le blanc de réactifs pour le point de concentration basse. Les courbes de calibrations sont déterminées avec 2 points, pour autoriser l'analyse de concentrations maximales pour chaque élément dans les échantillons inconnus. La précision des déterminations en conditions de routine ainsi que la reproductibilité de l'opération de lessivage et la précision instrumentale des analyses ont étéévaluées. Les déviations standards relatives (RSD) sont de 1,2% pour tout élément dont les concentrations dans le solide sont au dessus des limites de quantification. Les limites de détection de la méthode dans les solutions tamponnées ont aussi étéévaluées. Enfin, pour évaluer la justesse de cette méthode "micro-ondes - DCP" huit charbons certifiés matériaux de référence de différents types ont été analysés, et sont en bon accord avec les données certifiées ou seulement disponibles publiées. Les données sur un certain nombre d'oxydes d'éléments majeurs actuellement non certifiés sont présentées pour les matériaux de référence AR. [source] Determination of halofantrine and its main metabolite desbutylhalofantrine in rat plasma by high-performance liquid chromatography with on-line UV irradiation and peroxyoxalate chemiluminescence detectionBIOMEDICAL CHROMATOGRAPHY, Issue 1 2009Abena Amponsaa-Karikari Abstract A sensitive, selective and reliable method has been developed and validated for the determination of halofantrine and its metabolite desbutylhalofantrine in rat plasma using 9,10-diphenylanthracene as an internal standard. The method is based on peroxyoxalate chemiluminescence detection of hydrogen peroxide produced from fused aromatic rings in the structures of halofantrine and desbutylhalofantrine upon UV irradiation. Using spiked rat plasma, good linear relationships were obtained for both halofantrine and desbutylhalofantrine between peak height ratios (vs internal standard) and their corresponding concentrations over a range of 0.01,0.8 µg/mL with correlation coefficients of at least 0.997. The detection limits at signal-to-noise ratio of 3 using 0.2 mL of rat plasma were 1.5 and 1.4 ng/mL for halofantrine and desbutylhalofantrine, respectively. Relative standard deviations (n = 3) intra- and inter-day were between 0.5 and 5.4% for all the studied concentrations. Using this method with simple sample treatment, halofantrine and desbutylhalofantrine in rat plasma could be precisely determined without interference from endogenous substances. The method was successfully applied to the measurement of the time courses of plasma halofantrine concentration after oral administration of the drug (7 mg/kg) to rats. Copyright © 2008 John Wiley & Sons, Ltd. [source] An improved validated ultra high pressure liquid chromatography method for separation of tacrolimus impurities and its tautomersDRUG TESTING AND ANALYSIS, Issue 3 2010Acharya Subasranjan Abstract A selective, specific and sensitive ultra high pressure liquid chromatography (UHPLC) method was developed for determination of tacrolimus degradation products and tautomers in the preparation of pharmaceuticals. The chromatographic separation was performed on Waters ACQUITY UPLC system and BEH C8 column using gradient elution of mobile phase A (90:10 v/v of 0.1% v/v triflouroacetic acid solution and Acetonitrile) and mobile phase B (90:10 v/v acetonitrile and water) at a flow rate of 0.6 mL min,1. Ultraviolet detection was performed at 210 nm. Tacrolimus, tautomers and impurities were chromatographed with a total run time of 25 min. Calibration showed that the response of impurity was a linear function of concentration over the range 0.3,6 µg mL,1 (r2 , 0.999) and the method was validated over this range for precision, intermediate precision, accuracy, linearity and specificity. For precision study, percentage relative standard deviation of each impurity was < 15% (n = 6). The method was found to be precise, accurate, linear and specific. The proposed method was successfully employed for estimation of tacrolimus impurities in pharmaceutical preparations. Copyright © 2010 John Wiley & Sons, Ltd. [source] The Influence of the Cathodic Pretreatment on the Electrochemical Detection of Dopamine by Poly(1-aminoanthracene) Modified ElectrodeELECTROANALYSIS, Issue 19 2010Estela de Pieri Troiani Abstract In this study we demonstrated the influence of the cathodic pretreatment of poly(1-aminoanthracene) (PAA) electropolymerized on a platinum electrode for determination of dopamine (DA). The DA electrochemical response was obtained after a cathodic pretreatment of the PAA electrode which consisted of applying a potential of ,0.7,V (vs. Ag/AgCl) for 3,s before each measurement. The pretreatment of the electrode changed the PAA electrocatalytic properties so that the electrode began to present electrochemical response to DA without interference of ascorbic acid (AA). The anodic peak currents determined by differential pulse voltammetry using pretreated PAA showed a linear dependence on the DA concentration from 0.56 to 100,µM with a detection limit of 0.13,µM and a correlation coefficient of 0.9986. The electrode exhibits a relative standard deviation of 1.2,% for ten successive measurements of a 0.5,mM DA solution. The analysis by scanning electron microscopy and atomic force microscopy show a homogeneous and nanostructured film with globular structures with diameter of about 20,nm. The analytical results obtained for DA determination at a pretreated PAA electrode in pharmaceutical formulation sample were in good agreement with those obtained by a comparative procedure at a 95,% confidence level. PAA electrode after the pretreatment showed electrochemical responses to DA with excellent selectivity, sensitivity, and high stability without interference of AA. [source] Stripping Voltammetry of Cerium(IIl) with a Chemically Modified Carbon Paste Electrode Containing Functionalized Nanoporous Silica GelELECTROANALYSIS, Issue 2 2008Mehran Javanbakht Abstract This research introduces the design of an adsorptive stripping voltammetric method for the cerium(III) determination at a carbon paste electrode, chemically modified with dipyridyl-functionalized nanoporous silica gel (DPNSG-CPE). The electroanalytical procedure comprised two steps: the Ce(III) chemical accumulation at ,200,mV followed by the electrochemical detection of the Ce(III)/dipyridyl complex, using anodic stripping voltammetry. The factors, influencing the adsorptive stripping performance, were optimized including the modifier quantity in the paste, the electrolyte concentrations, the solution pH and the accumulation potential or time. The resulting electrode demonstrated a linear response over a wide range of Ce(III) concentration (1.0,28,ng mL,1). The precision for seven determinations of 4 and 10,ng mL,1 Ce(III) was 3.2% and 2.5% (relative standard deviation), respectively. The prepared electrode was used for the cerium determination in real samples and very good recovery results were obtained. [source] Electrocatalytic Reduction of Nitrite Ion on a Toluidine Blue Sol-Gel Thin Film Electrode Derived from 3-Aminopropyl Trimethoxy SilaneELECTROANALYSIS, Issue 22 2007K. Thenmozhi Abstract An organically modified sol-gel electrode using 3-aminopropyltrimethoxy silane for covalent immobilization of a redox mediator namely toluidine blue has been reported. Cyclic voltammetric characterization of the modified electrode in the potential range of 0.2,V to ,0.6,V exhibited stable voltammetric behavior in aqueous supporting electrolyte with a formal potential of ,0.265,V vs. SCE, corresponding to immobilized toluidine blue. The electrocatalytic activity of the modified electrode when tested towards nitrite ion exhibited a favorable response with the electrocatalytic reduction of nitrite occurring at a reduced potential of ,0.34,V. A good linear working range from 2.94×10,6,M to 2.11×10,3,M with a detection limit of 1.76×10,6,M and quantification limit of 5.87×10,6,M was obtained for nitrite determination. The stable and quick response (4,s) of the modified electrode towards nitrite under hydrodynamic conditions shows the feasibility of using the present sensor in flow systems. Significant improvements in the operational stability by overcoming the leachability problem and repeatability with a relative standard deviation of 1.8% of the TB thin film sensor have been obtained by the strategy of immobilization of the mediator in the sol-gel matrix. [source] Bismuth Film Electrode as an Alternative for Mercury Electrodes: Determination of Azo Dyes and Application for Detection in Food StuffsELECTROANALYSIS, Issue 21 2007Benoît Claux Abstract Bismuth electrodes were investigated and exhibit electrochemical properties similar to mercury electrodes but with much lower toxicity. An electrochemical application of bismuth film modified glassy carbon electrode for azo dyes determination was investigated. The plating step was optimized in order to achieve its analytical efficiency. A plating potential of ,0.9,V in a solution of 200,mg/L Bi(NO3)3, 0.5,M HNO3 for 100,s yields to a suitable electrode (in terms of stability and detection). Azo dyes such as azorubine (i.e., carmoisine, E122), amaranth (E123), ponceau 4R (i.e., new coccine, E124) and allura red (E129) were determined by differential pulse voltammetry in a NaCl solution in the concentration range of few ppm to 100 ppm. The reproducibility of the signal, characterized by the relative standard deviation, was found to be less than 5%, the detection and quantification limits were few mg/L. The influence of other food components on the signal was studied and the applicability was tested on real beverages samples. [source] Voltammetric Sensor for Sodium Nitroprusside Determination in Biological Fluids Using Films of Poly- L -LysineELECTROANALYSIS, Issue 9 2007Claudece Pereira, Francisco Abstract Sodium nitroprusside (NP), a commercial vasodilator, can be pre-concentrated on vitreous carbon electrode modified by films of 97.5%: 2.5% poly- L -lysine (PLL): glutaraldehyde (GA). This coating gives acceptable anion exchange properties whilst giving the required improvement of adhesion to the glassy carbon electrode surface. Linear response range and detection limit on nitroprusside in B-R buffer pH,4.0, were 1×10,6 to 2×10,5 mol L,1 and 1×10,7 mol L,1, respectively. The repeatability of the proposed sensor, evaluated in term of relative standard deviation, was measured as 4.1% for 10 experiments. The voltammetric sensor was directly applied to determination of nitroprusside in human plasma and urine samples and the average recovery for these samples was around 95,97% without any pre treatment. [source] Disposable Screen-Printed Edge Band Ultramicroelectrodes for the Determination of Trace Amounts of Nitrite IonELECTROANALYSIS, Issue 10 2006Jen-Lin Chang Abstract The application of linear scan voltammetry for sensitive determination of nitrite by using a disposable screen-printed edge band carbon ultramicroelectrode (designated as SPUME) was reported in this study. The measurement with the SPUME can be performed in solutions of low ionic strength, e.g., natural waters, because the ohmic loses are negligible. The limiting oxidation current of nitrite showed a wide linear range up to 3,mM at the SPUME. A relative standard deviation of 2.46% (n=5) for analyzing 5,,M nitrite indicated a detection limit (S/N=3) of 0.38,,M. Real sample analysis of mineral and ground water samples as well as bratwurst food product showed satisfactory results. Since the SPUME is low cost and easy for mass production, the disposable nature further offers to application in diverse field of electroanalytical chemistry. [source] The Electrochemical Properties of Co(TPP), Tetraphenylborate Modified Glassy Carbon Electrode: Application to Dopamine and Uric Acid AnalysisELECTROANALYSIS, Issue 5 2006Yunlong Zeng Abstract We report the combination of the charge repelling property of tetraphenyl-borate (TPB) anion and the electrooxidation catalytic effect of cobalt(II) tetrakisphenylporphyrin (CoTPP) embedded in a sol gel ceramic film to develop a modified glassy carbon electrode (CoTPP-TPB-SGGCE) for the simultaneous determination of dopamine (DA) and uric acid (UA). The optimized CoTPP-TPB-SGGCE shows excellent sensitivity and selectivity for the DA and UA analysis. As high as 2000 fold acceptable tolerance of ascorbic acid (AA) for the determination of trace DA and UA is reached. In the presence of 0.10,mM AA, the linear concentration range for DA is from 6.0×10,8 to 2.5×10,5,M, and the detection limit is 2.0×10,8,M. For UA, the linear concentration range is from 1.0×10,7 to 3.5×10,5,M, and the detection limit is 7.0×10,8,M. Our study has also demonstrated that the novel CoTPP-TPB-SGGCE shows high stability and reliability. For 6.00,,M DA and UA, a total of 12,measurements were taken in one week, and the relative standard deviation is 2.05% and 2.68% respectively. No obvious shift of peak current and peak potential is observed over a three-month lifetime test. The response of the sensor is very quick and response time is approximately 1,s. Satisfactory results are also achieved when the CoTPP-TPB-SGGCEs being used to detect the DA and UA in human urine samples. [source] Adsorptive Stripping Voltammetric Determination of Trace Uranium with a Bismuth-Film Electrode Based on the U(VI),U(V) Reduction Step of the Uranium-Cupferron ComplexELECTROANALYSIS, Issue 3 2006Georgia Kefala Abstract This work reports the use of adsorptive stripping voltammetry (AdSV) for the determination of uranium on a preplated rotating-disk bismuth-film electrode (BiFE). The principle of the method relied on the complexation of U(VI) ions with cupferron and the subsequent adsorptive accumulation of the complex on the surface of the BiFE. The uranium in the accumulated complex was then reduced by means of a cathodic voltammetric scan while the analytically useful U(VI),U(V) reduction signal was monitored. The experimental variables as well as potential interferences were investigated and the figures of merit of the method were established. Using the selected conditions, the 3, limit of detection for uranium was 0.1,,g L,1 at a preconcentration time of 480,s and the relative standard deviation was 4.7% at the 5,,g L,1 level for a preconcentration time of 120,s (n=8). The accuracy of the method was established by analyzing a reference sea water sample. [source] Barrel Plating Rhodium Electrode: Application to Flow Injection Analysis of HydrazineELECTROANALYSIS, Issue 14 2005Jun-Wei Sue Abstract We introduce here the application of barrel plating technology for mass production of disposable-type electrodes. Easy for mass production, barrel plating rhodium electrode (Rh-BPE) is for the first time demonstrated for analytical application. Hydrazine was chosen as a model analyte to elucidate the electrocatalytic and analytical ability of the Rh-BPE system in pH,7 phosphate buffer solution. Flow injection analysis (FIA) of hydrazine showed a linear calibration range of 25,1000,ppb with a slope and a regression coefficient of 5,nA/ppb and 0.9946, respectively. Twenty-two replicate injections of 25,ppb hydrazine showed a relative standard deviation of 3.17% indicating a detection limit (S/N=3) of 2.5,ppb. The system can be continuously operated for 1 day without any alteration in the FIA signals and is tolerable to the interference of oxalic acid, gelatine, Triton X-100, and albumin for even up to 100 times excess in concentration with respect to 400,ppb hydrazine. Since the fabrication cost of the electrode is cheap, it is thus disposable in nature. Furthermore, barrel plating technique can be extendable to other transition metals for application in many fields of research interest. [source] Trace Determination of Chromium by Square-Wave Adsorptive Stripping Voltammetry on Bismuth Film ElectrodesELECTROANALYSIS, Issue 21 2004Eleni Chatzitheodorou Abstract This works reports the use of adsorptive stripping voltammetry (AdSV) for the trace determination of chromium on a rotating-disk bismuth-film electrode (BFE). During the reductive accumulation step, all the chromium species in the sample were reduced to Cr(III) which was complexed with cupferron and the complex was accumulated by adsorption on the surface of a preplated BFE. The stripping step was carried out by using a square-wave (SW) potential-time voltammetric signal. Electrochemical cleaning of the bismuth film was employed, enabling the same bismuth film to be used for a series of measurements in the presence of dissolved oxygen. The experimental variables as well as potential interferences were investigated and the figures of merit of the method were established. Using the selected conditions, the 3, limit of detection for chromium was 100,ng L,1 (for 120,s of preconcentration) and the relative standard deviation was 3.6% at the 2,,g L,1 level (n=8). Finally, the method was applied to the determination of chromium in real samples with satisfactory results. [source] Heavy Metals in Matrices of Food Interest: Sequential Voltammetric Determination at Trace and Ultratrace Level of Copper, Lead, Cadmium, Zinc, Arsenic, Selenium, Manganese and Iron in MealsELECTROANALYSIS, Issue 18 2004Clinio Locatelli Abstract The voltammetric methods are very suitable and versatile techniques for the simultaneous metal determination in complex matrices. The present work, regarding the sequential determination of Cu(II), Pb(II), Cd(II), Zn(II) by square-wave anodic stripping voltammetry (SWASV), As(III), Se(IV) by square-wave cathodic stripping voltammetry (SWCSV) and Mn(II), Fe(III) by square-wave voltammetry (SWV) in matrices involved in foods and food chain as wholemeal, wheat and maize meal, are an interesting example of the possibility to sequentially determine each single element in real samples. Besides the set up of the analytical method, particular attention is aimed either at the problem of possible signal interference or to show that, using the peak area Ap as instrumental datum, it is possible to achieve lower limits of detection. The analytical procedure was verified by the analysis of the standard reference materials: Wholemeal BCR-CRM 189, Wheat Flour NIST-SRM 1567a and Rice Flour NIST-SRM 1568a. Precision, as repeatability, and accuracy, expressed as relative standard deviation and relative error, respectively, were lower than 6% in all cases. In the presence of reciprocal interference, the standard addition method considerably improved the resolution of the voltammetric technique. Once set up on the standard reference materials, the analytical procedure was transferred and applied to commercial meals sampled on market for sale. A critical comparison with spectroscopic measurements is also discussed. [source] The Electrochemical Behavior of ,-Ketoglutarate at the Hanging Mercury Drop Electrode in Acidic Aqueous Solution and Its Practical Application in Environmental and Biological SamplesELECTROANALYSIS, Issue 12 2004Li Yang Abstract The voltammetric behavior of ,-ketoglutarate (,-KG) at the hanging mercury drop electrode (HMDE) has been investigated in acetate buffer solution. Under the optimum experimental conditions (pH,4.5, 0.2,M NaAc-HAc buffer solution), a sensitive reductive wave of ,-KG was obtained by linear scan voltammetry (LSV) and the peak potential was ,1.18,V (vs. SCE), which was an irreversible adsorption wave. The kinetic parameters of the electrode process were ,=0.3 and ks=0.72,1/s. There was a linear relationship between peak current ip, ,-KG and ,-KG concentration in the range of 2×10,6,8×10,4,M ,-KG. The detection limit was 8×10,7,M and the relative standard deviation was 2.0% (C,-KG=8×10,4,M, n=10). Applications of the reductive wave of ,-KG for practical analysis were addressed as follows: (1) It can be used for the quantitative analysis of ,-KG in biological samples and the results agree well with those obtained from the established ultraviolet spectrophotometric method. (2) Utilizing the complexing effect between ,-KG and aluminum, a linear relationship holds between the decrease of peak current of ,-KG ,ip and the added Al concentration C in the range of 5.0×10,6,2.5×10,4,M. The detection limit was 2.2×10,6,M and the relative standard deviation was 3.1% (C=4×10,5,M, n=10). It was successfully applied to the detection of aluminum in water and synthetic biological samples with satisfactory results, which were consistent with those of ICP-AES. (3) It was also applied to study the effect of AlIII on the glutamate dehydrogenase (GDH) activity in the catalytically reaction of ,-KG+NH+NADH,L -glutamate+NAD++H2O by differential pulse polarography (DPP) technique. By monitoring DPP reductive currents of NAD+ and ,-KG, an elementary important result was found that Al could greatly affect the activity of GDH. This study could be attributed to intrinsic understanding of the aluminum's toxicity in enzyme reaction processes. [source] Electrocatalytic Oxidation of NADH by Oxidized s-Adenosyl-L-Methionine (SAMe): Application to NADH and SAMe DeterminationsELECTROANALYSIS, Issue 11 2004Noemí de-los-Santos-Álvarez Abstract s -Adenosyl- L -methionine (SAMe) is an adenosine analogue with therapeutical activity against affective disorders and liver dysfunctions. It can be oxidized on graphite electrode yielding a strongly adsorbed electroactive oxidation product for which a quinone-imine structure is proposed. This compound is capable of electrocatalyzing the NADH oxidation at low potentials, lowering the overvoltage by about 300,mV. An amperometric method for NADH determination at +0.1,V (Ag|AgCl|KClsat) is developed using an oxidized-SAMe-modified electrode in pH,9. Linear calibration plots were obtained with a detection limit of 2.4,nM. The electrode response time and the relative standard deviation of the slope of the calibration plot for 5 different modified electrodes were 12,s and 5.6% respectively. The catalytic scheme also provides the first method to determine SAMe itself by adsorptive differential pulse voltammetry. The linear range was found to be 42.4,424,nM with a reproducibility of 6.9%. The method was applied to SAMe determination in a pharmaceutical formulation. [source] A Study of the Determination of Cu(II) by Anodic Stripping Voltammetry on a Novel Nylon/Carbon Fiber ElectrodeELECTROANALYSIS, Issue 7 2004A. Mylonakis Abstract In this work we report a new electrode material formed by injection-moulding of a conducting polymer consisting of carbon fibers in a Nylon matrix. This material is highly conductive, inexpensive, easy to mould in different shapes and requires minimal pretreatment. The electrode was tested as a mercury-free sensor for the trace determination of Cu(II) by anodic stripping voltammetry (ASV). The deposition and stripping behavior of copper on the conducting material was initially studied by cyclic voltammetry and the chemical and instrumental parameters of the determination were investigated. The electrode has been shown to be suitable for the determination of Cu(II) in the range 8,,g L,1 to 30,mg,L,1 (with deposition times ranging from 30,s to 10,min) with a relative standard deviation of 2.2% (at the 0.5,mg,L,1 level) and a limit of detection of 8,,g L,1 Cu(II) for 10,min of accumulation (at a S/N ratio of 5). The electrode was, finally, applied to the determination of copper in tap-water, pharmaceutical tablets and bovine serum with recoveries of 97.4, 94.9 and 93.4%, respectively [source] Voltammetric Determination of Free and Total Sulfur Dioxide in BeerELECTROANALYSIS, Issue 5-6 2003J. Almeida Abstract A voltammetric method for the determination of free and total sulfur dioxide in beer is described. First, volatile aldehydes (mainly acetaldehyde) are purged with nitrogen from a beer sample diluted in alkaline medium, collected in an appropriate electrolyte trapping solution and determined, after derivatization with hydrazine, by voltammetry using a hanging mercury drop electrode. Then, the remaining beer solution is strongly acidified and (total) sulfur dioxide is purged with nitrogen, collected in an appropriate electrolyte trapping solution and determined by voltammetry. The free sulfur dioxide concentration is calculated by difference between (total) sulfur dioxide and acetaldehyde concentrations. The proposed method has a relative standard deviation of about 2.1% and 4.4%, respectively for (total) sulfur dioxide and free sulfur dioxide concentrations normally found in beer, and results are in good agreement with those obtained by the p -rosaniline reference method. [source] Determination of gaseous and particulate carbonyls in air by gradient-elution micellar electrokinetic capillary chromatographyELECTROPHORESIS, Issue 19 2008Hui Sun Abstract A new continuous-flow gradient-elution micellar electrokinetic capillary chromatography method is developed for the determination of airborne carbonyls after derivatization with 2,4-dinitrophenylhydrazine. A total of 16 carbonyls can be determined with detection limits ranging from 0.94 to 8.50,mg/L, working range from 4.72 to 346,mg/L, and repeatabilities (relative standard deviation, n=5) from 1.23 to 4.6% or 3.93 to 7.6% for migration time and peak area, respectively. Coupling with denuder-filter sampling, a preliminary survey has been conducted to determine gaseous and particulate carbonyls from air sampled at a roadside station. The method is shown to have sufficient sensitivity for 1-h sampling of ambient carbonyls with detection limits ranging from 0.045 to 1.2,,g/m3 and working range from 0.11 to 43.3,,g/m3 at a flow rate of 10,Lpm. The method requires minimal modification of commercially available capillary electrophoresis equipment and can differentiate gaseous and particulate carbonyls to provide essential information and objective data for adopting effective measures to combat the discharge of carbonyl compounds to the atmosphere. [source] New supported liquid membrane-capillary electrophoresis in-line arrangement for direct selective analysis of complex samplesELECTROPHORESIS, Issue 15 2006Leonor Nozal Abstract An in-line coupling of a micro-membrane extraction unit, based on supported liquid membrane, with commercially available capillary electrophoresis equipment is described. A main characteristic of this micro-membrane device, made from a simple Eppendorf tube, is that it permits the application of voltage in the acceptor solution to be applied during the extraction process. This has been shown as an alternative to enhance sensitivity, as the analytical signal achieved by applying 10,kV for 20,min was similar to that obtained without the application of voltage and with extraction time of 60,min. In addition, the design has been made permitting both in-line hydrodynamic and electrokinetic sample introduction into the electrophoretic capillary. The analytical potential of the proposed system has been demonstrated by the direct determination of nitroimidazoles from pig liver tissue. The high efficiency of the proposed system allowed the extraction and the determination of the analytes to be performed from a simple tissue homogenate obtained in water. The precision of the analysis of spiked samples, expressed in terms of relative standard deviation, was better than 4.8%. [source] Microchip capillary electrophoresis with a cellulose-DNA-modified screen-printed electrode for the analysis of neurotransmittersELECTROPHORESIS, Issue 15 2005Muhammad Johirul Abstract A microfluidic chip based on capillary electrophoresis coupled with a cellulose-single-stranded DNA (cellulose-ssDNA) modified electrode was used for the simultaneous analysis of dopamine (DA), norepinephrine (NE), 3,4-dihydroxy- L -phenylalanine (L -DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), and ascorbic acid (AA). The modification of the electrode improved the electrophoretic analysis performance by lowering the detection potential and enhancing the signal-to-noise characteristic without surface poisoning of the electrode. The sensitivity of the modified electrode was about 12 times higher than those of the bare ones. The test compounds were separated using a 62,mm long separation channel at the separation field strength of +200,V/cm within 220,s in a 10,mM phosphate buffer (pH,7.4). The most favorable potential for the amperometric detection was 0.7,V (vs. Ag/AgCl). A reproducible response (relative standard deviation of 1.3, 1.3, 2.1, 3.1, 3.4% for DA, NE, L -DOPA, DOPAC, and AA, respectively, for n,=,9) for repetitive sample injections reflected the negligible electrode fouling at the cellulose-ssDNA modified electrode. Square-wave voltammetric analyses reflected the sensitivities of the modified electrode for DA, NE, L -DOPA, DOPAC, and AA which were 1.78, 0.82, 0.69, 2.45, and 1.23,nC/µM with detection limits of 0.032, 0.93, 1.13, 0.31, and 0.62,µM, respectively. The applicability of this microsystem to real sample analysis was demonstrated. [source] Development of a new hybrid technique for rapid speciation analysis by directly interfacing a microfluidic chip-based capillary electrophoresis system to atomic fluorescence spectrometryELECTROPHORESIS, Issue 11 2005Feng Li Abstract This paper represents the first study on direct interfacing of microfluidic chip-based capillary electrophoresis (chip-CE) to a sensitive and selective detector, atomic fluorescence spectrometry (AFS) for rapid speciation analysis. A volatile species generation technique was employed to convert the analytes from the chip-CE effluent into their respective volatile species. To facilitate the chip-CE effluent delivery and to provide the necessary medium for subsequent volatile species generation, diluted HCl solution was introduced on the chip as the makeup solution. The chip-CE-AFS interface was constructed on the basis of a concentric "tube-in-tube" design for introducing a KBH4 solution around the chip effluent as sheath flow and reductant for volatile species generation as well. The generated volatile species resulting from the reaction of the chip-CE effluent and the sheath flow were separated from the reaction mixture in a gas-liquid separator and swept into the AFS atomizer by an argon flow for AFS determination. Inorganic mercury (Hg(II)) and methylmercury (MeHg(I)) were chosen as the targets to demonstrate the performance of the present technique. Both mercury species were separated as their cysteine complexes within 64 s. The precision (relative standard deviation, RSD, n = 5) of migration time, peak area, and peak height for 2 mg·L,1 Hg(II) and 4 mg·L,1 MeHg(I) (as Hg) ranged from 0.7 to 0.9%, 2.1 to 2.9%, and 1.5 to 1.8%, respectively. The detection limit was 53 and 161 µg·L,1 (as Hg) for Hg(II) and MeHg(I), respectively. The recoveries of the spikes of mercury species in four locally collected water samples ranged from 92 to 108%. [source] Urtica dioica agglutinin: Separation, identification, and quantitation of individual isolectins by capillary electrophoresis and capillary electrophoresis,mass spectrometryELECTROPHORESIS, Issue 9 2005Markus Ganzera Abstract With benign prostatic hyperplasia (BPH) being a major health problem in ageing men, alternative therapeutic approaches (e.g., with phytopharmaceuticals) are of great interest. Based on pharmacological evidences, one of the most promising options in that respect are the lectins found in Urtica dioica (stinging nettle) roots. In this study the qualitative and quantitative analysis of individual isolectins in U. dioica extracts is described, which is the first report on using capillary electrophoresis (CE) for the analysis of lectins in plant material at all. By utilizing a 200 mM sodium acetate buffer (pH 3.75) a baseline separation and determination of four closely related isolectins was feasible within 20 min in the aqueous plant extracts. The individual compounds were identified based on reference compounds as well as data obtained from CE-mass spectrometry (MS) experiments. After modifying the optimized CE conditions to 100 mM ammonium formate buffer with pH 3.75 and a voltage of 15 kV, the isolectins were clearly assignable in positive electrospray ionization (ESI) mode. The quantitative results obtained by CE (the total lectin content varied from 0 to 0.42% in the samples) were accurate (recovery rates of spiked samples between 92.5 and 96.2%), precise (relative standard deviation < 5%) and in good agreement to those obtained by High-performance liquid chromatography (HPLC). As for peak resolution, assignable compounds and required separation time the newly developed CE method was clearly advantageous over the determination achieved by LC. [source] Application of dodecyldimethyl (2-hydroxy-3-sulfopropyl) ammonium in wall modification for capillary electrophoresis separation of proteinsELECTROPHORESIS, Issue 3 2005Wei Wei Abstract A zwitterionic surfactant, dodecyldimethyl (2-hydroxy-3-sulfopropyl) ammonium (C12H25N+(CH3)2CH2CHOHCH2SO3,), named dodecyl sulfobetaine (DSB), was used as a novel modifier to coat dynamically capillary walls for capillary electrophoresis separation of basic proteins. The DSB coating suppressed the electroosmotic flow (EOF) in the pH range of 3,12. At high DSB concentration, the EOF was suppressed by more than 8.8,times. The DSB coating also prevented successfully the adsorption of cationic proteins on the capillary wall. Anions, such as Cl,, Br,, I,, SO42,, CO32,, and ClO4,, could be used as running buffer modifiers to adjust the EOF for better separation of analytes. Using this dynamically coated capillary, a mixture of eight inorganic anions achieved complete separation within 4.2,min with the efficiencies from 24,000 to 1,310,000,plates/m. In the presence of ClO4, as EOF adjustor, the separation of a mixture containing four basic proteins (lysozyme, cytochrome c, ,-chymotrypsinogen,A, and myoglobin) yielded efficiencies of 204,000,896,000,plates/m and recoveries of 88%,98%. Migration time reproducibility of these proteins was less than 0.5% relative standard deviation (RSD) from run to run and less than 3.1% RSD from day to day, showing promising application of this novel modifier in protein separation. [source] Determination of the chiral and achiral related substances of methotrexate by cyclodextrin-modified micellar electrokinetic chromatographyELECTROPHORESIS, Issue 16 2004Roberto Gotti Abstract A cyclodextrin-modified micellar electrokinetic chromatographic (CD-MEKC) method for the determination of the most important potential impurities of methotrexate (MTX): 2,4-diamino-6-(hydroxymethyl)pteridine, aminopterine hydrate, 4-[N -(2-amino-4-hydroxy-6-pteridinylmethyl)- N -methylamino] benzoic acid, 4-[N -(2,4-diamino-6-pteridinylmethyl)- N -methylamino] benzoic acid, and the distomer D -MTX is presented. The MEKC separation of these compounds was optimized by applying a step-by-step approach. The addition of ,-CD to a conventional MEKC system, based on sodium dodecyl sulfate (SDS) as surfactant, showed to be essential for the enantioresolution of racemic MTX as well as for the separation of the achiral impurities. To achieve high-resolution factor between the peaks adjacent to the main component (L -MTX), as required in the analysis of related impurities, the separation conditions were stressed; in particular, the addition of methanol to the CD-MEKC system resulted in a very effective choice. Under the optimized final conditions (100 mM SDS and 45 mM ,-CD in a mixture of 50 mM borate buffer, pH 9.30-methanol (75:25 v/v)), the method was validated showing a general adequate accuracy (93,106% recovery) in the determination of L -MTX related substances at the impurity level of 0.12% w/w with a relative standard deviation (RSD)% lower than 8% (n = 4). The method was successfully applied to the analysis of pharmaceuticals (tablets and injections) which showed to contain the distomer D -MTX as major impurity and aminopterine hydrate as a further related substance in the commercial tablets. [source] Comparison of two glutaraldehyde immobilization techniques for solid-phase tryptic peptide mapping of human hemoglobin by capillary zone electrophoresis and mass spectrometryELECTROPHORESIS, Issue 9 2004Isabelle Migneault Abstract Stabilization of proteolytic enzymes, especially by immobilization, is of considerable interest because of their potential applications in medicine and the chemical and pharmaceutical industries. We report here a detailed comparison of two procedures for trypsin immobilization using the same homobifunctional agent, glutaraldehyde, for the purpose of peptide mapping. These methods include covalent coupling either to controlled pore glass (solid support) or via a cross-linking reaction (without any solid support). The immobilized trypsin preparations were characterized by the determination of immobilization efficiency, which ranged from 68 to > 95%, and measurement of apparent kinetic parameters toward a synthetic peptide-like substrate. Batch digestions of whole denaturated human normal adult hemoglobin (HbA) were performed to obtain peptide maps by capillary zone electrophoresis (CZE). Migration time reproducibility of the CZE maps was excellent, with a mean relative standard deviation of 1.5%. Moreover, the two immobilized enzyme preparations showed excellent reproducibility for repeated digestions. Matrix-assisted laser desorption/ionization (MALDI)-mass spectrometry was also used for peptide mass mapping of denaturated HbA digested using the two immobilized trypsin preparations. Even though the two immobilized trypsin preparations do not behave identically, similar sequence coverages of 57% and 61% (for the two HbA chains merged) were achieved for the support-based and cross-linked trypsin preparations, respectively. [source] Protein-based electrochemical biosensor for detection of silver(I) ions,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2010Sona Krizkova Abstract Silver(I) ions are extremely toxic to aquatic animals. Hence, monitoring of these ions in the environment is needed. The aim of the present study was to suggest a simple biosensor for silver(I) ions detection. The suggested biosensor is based on the modification of a hanging mercury drop electrode (HMDE) by the heavy metal binding protein metallothionein (MT) for silver(I) ions detection. Metallothionein accumulated for 120 s onto the HMDE surface. After rinsing the electrode, the biosensor (MT modified HMDE) was prepared prior to detection of silver(I) ions. The biosensor was immersed in a solution containing silver(I) ions. These ions were bound to the MT structure. Furthermore, the electrode was rinsed and transferred to a pure supporting electrolyte solution, in which no interference was present. Under these experimental conditions, other signals relating to heavy metals naturally occurring in MT were not detected. This phenomenon confirms the strong affinity of silver(I) ions for MT. The suggested biosensor responded well to higher silver(I) ion concentrations. The relative standard deviation for measurements of concentrations higher than 50,µM was approximately 2% (n,=,8). In the case of concentrations lower than 10,µM, the relative standard deviation increased to 10% (n,=,8). The detection limit (3,signal/noise) for silver(I) ions was estimated as 500,nM. Environ. Toxicol. Chem. 2010;29:492,496. © 2009 SETAC [source] Ultra-trace analysis of multiple endocrine-disrupting chemicals in municipal and bleached kraft mill effluents using gas chromatography,high-resolution mass spectrometryENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2008Michael G. Ikonomou Abstract A comprehensive gas chromatographic,high-resolution mass spectrometric (GC-HRMS),based method was developed that permitted the simultaneous determination of 30 estrogenic endocrine-disrupting chemicals (EDCs) and related compounds, including surfactants, biogenic and synthetic steroids, fecal sterols, phytoestrogens, and plasticizers, in wastewater. Features of the method include low sample volume (,40 ml), optimized Florisil® cleanup to minimize matrix interferences and optimized analyte derivatization to improve sensitivity via GC-HRMS. Detection limits were in the low- to mid-ng/L range, and recoveries were greater than 60% for most target analytes. This new method allows for high throughput analysis of many organic wastewater contaminants in a complex matrix with relative standard deviation of less than 15% for most measurable compounds. The applicability of the method was demonstrated by examining wastewater samples from different origins. Compounds such as di(2-ethylhex-yl)phthalate, cholesterol, cholestanol, and other cholesterol derivatives were measured in much higher concentrations in untreated sewage and were reduced substantially in concentration by the treatment process. However, steroidal compounds, particularly estrone (E1), 17,-estradiol (E2), and estriol (E3), as well as plant sterols (except stigmastanol), were greater in the treated municipal wastewater versus the untreated effluent. Plant and fungi sterols, stigmastanol and ergosterol, were found largely associated with bleached kraft mill effluent (BKME) as compared to the municipal effluents. [source] Determination of cypermethrin in palm oil matricesEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 10 2009Badrul Hisyam Zainudin Abstract In this study, a new method was developed for the determination of cypermethrin residue in both crude palm oil (CPO) and crude palm kernel oil (CPKO) using GC with electron capture detector. In this method, the oil was extracted with acetonitrile. Aliquots were cleaned-up using combined solid phase extraction (SPE), and a primary-secondary amine in combination with graphitized carbon black. The SPE cartridges were first conditioned and then eluted with acetonitrile. Cypermethrin recoveries from the fortified CPO samples were 87,98% with relative standard deviation (RSD) values of 4,8%, while those for the fortified CPKO samples were 83,100% with RSD values of 3,10%. Since good recoveries were obtained with RSD values below 10% in most cases, the proposed methodology will be useful for the analyses of palm oil samples. The method was successfully applied to the analysis of cypermethrin in real palm oil samples from various parts of Malaysia. No cypermethrin residue was found among 30 samples analyzed. [source] | ||||||||||||||||||||||||||||||||||