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Selective Determination (selective + determination)
Selected AbstractsSelective Determination of Dopamine in the Presence of Ascorbic Acid at Porous-Carbon-Modified Glassy Carbon ElectrodesELECTROANALYSIS, Issue 11 2008Shuqing Song Abstract Selective dopamine (DA) determinations using porous-carbon-modified glassy carbon electrodes (GCE) in the presence of ascorbic acid (AA) were studied. The effects of structure textures and surface functional groups of the porous carbons on the electrochemical behavior of DA was analyzed based on both cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements. The differential pulse voltammetry of DA on the modified GCE was determined in the presence of 400-fold excess of AA, and the linear determination ranges of 0.05,0.99, 0.20,1.96, and 0.6,12.60,,M with the lowest detected concentrations of 4.5×10,3, 4.4×10,2, and 0.33,,M were obtained on the mesoporous carbon, mesoporous carbon with carboxylic and amino groups modified electrodes, respectively. [source] Selective determination of famotidine in human plasma by high performance liquid chromatography in alkaline media with solid phase extractionJOURNAL OF SEPARATION SCIENCE, JSS, Issue 8 2003Eva Anzenbacherová Abstract A new method is described for the determination of famotidine by solid phase extraction from alkalinized human plasma followed by reversed phase (RP) HPLC in acetonitrile/alkaline buffer with molsidomine as an internal standard. Different acetonitrile/aqueous buffer mobile phases as well as various RP columns were used. Alkaline medium allowed the limit of quantitation to be lowered to 5 ng/mL of plasma as the famotidine gives more intense absorption at about 286 nm (at pH values higher than 7). Moreover, work in alkaline media and at this wavelength is highly selective as peaks corresponding to impurities present in most samples are well separated. A method using a mildly alkaline mobile phase (acetonitrile/10 mM phosphate with 10 mM 1-heptanesulphonic acid, pH 7.5) was successfully used for determination of famotidine in human plasma in a pharmacokinetic study. [source] Preparation, Characterization and Analytical Applications of a New and Novel Electrically Conducting PolymerELECTROANALYSIS, Issue 15 2006F. D'Eramo Abstract In this study, a glassy carbon electrode (GC) was modified with an electropolymerized film of 1-naphthylamine (1-NAP) with a subsequent overoxidation treatment in 0.2,M sodium hydroxide solution. This polymer p-1-NAPox film coated GC electrode was used for the selective determination of dopamine (DA) in the presence of a triple concentration of ascorbic acid (AA). These studies were performed using cyclic voltammetry and square-wave voltammetry at physiological pH. p-1-NAPox shows an attractive permselectivity, a marked enhancement of the current response and antifouling properties when compared to a bare GC electrode activated in basic media. With a preconcentration time of 3,minutes at open circuit, linear calibration plots were obtained for DA in buffer solution (pH,7.4) over the concentration range from 1×10,6,1×10,4 M with a detection limit of 1.59×10,7 M. [source] Adsorptive Stripping Voltammetry of Rifamycins at Unmodified and Surfactant-Modified Carbon Paste ElectrodesELECTROANALYSIS, Issue 20 2004Sonia Gutiérrez-Fernández Abstract The electrochemical behavior of the antibiotics rifampicin and rifamycin SV is investigated by cyclic voltammetry at carbon paste and in situ surfactant modified carbon paste electrodes. Both antibiotics adsorb on the unmodified electrodes and show a reversible redox process due to the oxidation of the 6,9-dihydroxynaphthalene moiety to the corresponding naphthoquinone. This process is used as analytical signal for developing adsorptive voltammetric methods for the determination of the antibiotics. Experimental parameters, such as pH of the supporting electrolyte, accumulation potential and time are optimized. After accumulation from acidic solutions (0.1,M KCl pH 2 or HCl 0.2,M) at ,0.1 or 0,V for 3,min, the differential pulse oxidation peak current changes linearly with the antibiotic concentration in the range 3.5×10,10,M ,5.4×10,9,M or 5×10,11,M ,1.0×10,9,M for rifampicin and rifamycin SV, respectively. Rifamycin SV is not accumulated on carbon paste electrodes modified in situ with the anionic surfactant sodium dodecyl sulfate, whereas rifampicin is readily accumulated on this modified electrodes resulting in a signal enhancement and allowing rifampicin determinations without interference from rifamycin SV. On the other hand, selective determination of rifamycin SV in the presence of rifampicin is achieved by using carbon paste electrodes in situ modified with the cationic surfactant cetyltrimethylammonium chloride. [source] Quantification of fudosteine in human plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry employing precolumn derivatization with 9-fluorenylmethyl chloroformateJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2006Fengguo Xu Abstract This paper describes a novel method for the sensitive and selective determination of fudosteine in human plasma. The method involves a derivatization step with 9-fluorenylmethyl chloroformate (FMOC-Cl) in borate buffer and detection based on high-performance liquid chromatography-electrospray ionization mass spectrometry (LC/ESI/MS). After acetonitrile-induced protein precipitation of plasma samples, fudosteine was derivatized with FMOC-Cl, then extracted by ethyl acetate, evaporated, reconstituted and injected using an LC/ESI/MS instrument. Separation was achieved using an ODS column and isocratic elution. Excellent linearity was obtained for the entire calibration range from 0.05 to 20 µg/ml. Validation assays of the lower limit of quantification (LLOQ) as well as for the intra- and inter-batch precision and accuracy met the international acceptance criteria for bioanalytical method validation. Using the developed analytical method, fudosteine could be detected for the first time in human plasma with a low limit of detection (LLOD) of 0.03 µg/ml. The proposed method has been successfully applied to study the pharmacokinetics of fudosteine in healthy Chinese volunteers after single and multiple oral administration. Copyright © 2006 John Wiley & Sons, Ltd. [source] Application of functional group modified substrate in room temperature phosphorescence, II,heavy atom-chelated filter paper for selective determination of , -naphthalene acetic acidLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 4-5 2005Ruohua Zhu Abstract Heavy atom-chelated filter paper was synthesized and used as the substrate for room-temperature phosphorescence (RTP). The synthesis conditions for chelated paper were studied. The Pb-chelated filter paper could selectively induce the RTP of , -naphthalene acetic acid (, -NAA). The excitation and emission wavelengths of RTP of , -NAA were 300 nm and 521 nm, respectively. The concentration of , -NAA was linear with the RTP intensity in the range 2 × 10,6,6 × 10,4 mol/L (correlation coefficient, 0.9999). The concentration detection limit was 1.35 × 10,7 mol/L and the absolute detection limit was 0.25 ng/spot. The RSD (n = 10) was 1.7%. The method was applied to the analysis of water and vegetable samples with satisfactory results. Because the heavy atom was directly chelated onto the filter paper, the heavy-atom effect on the RTP of NAA was further increased and the analysis procedure was simple, fast and economical. Copyright © 2005 John Wiley & Sons, Ltd. [source] High-performance liquid chromatography/mass spectrometric and proton nuclear magnetic resonance spectroscopic studies of the transacylation and hydrolysis of the acyl glucuronides of a series of phenylacetic acids in buffer and human plasmaRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2010Elin S. Karlsson The use of high-performance liquid chromatography/mass spectrometry (HPLC/MS) and proton nuclear magnetic resonance (1H NMR) spectroscopy for the kinetic analysis of acyl glucuronide (AG) isomerisation and hydrolysis of the 1-,- O -acyl glucuronides (1-,- O -AG) of phenylacetic acid, (R)- and (S)-,-methylphenylacetic acid and ,,,-dimethylphenylacetic acid is described and compared. Each AG was incubated in both aqueous buffer, at pH 7.4, and control human plasma at 37°C. Aliquots of these incubations, taken throughout the reaction time-course, were analysed by HPLC/MS and 1H NMR spectroscopy. In buffer, transacylation reactions predominated, with relatively little hydrolysis to the free aglycone observed. In human plasma incubations the calculated rates of reaction were much faster than for buffer and, in contrast to the observations in buffer, hydrolysis to the free aglycone was a significant contributor to the overall reaction. A diagnostic analytical methodology based on differential mass spectrometric fragmentation of 1-, -O- AGs compared to the 2-, 3- and 4-positional isomers, which enables selective determination of the former, was confirmed and applied. These findings show that HPLC/MS offers a viable alternative to the more commonly used NMR spectroscopic approach for the determination of the transacylation and hydrolysis reactions of these AGs, with the major advantage of having the capability to do so in a complex biological matrix such as plasma. Copyright © 2010 John Wiley & Sons, Ltd. [source] High Sensibility of Quantum Dots to Metal Ions Inspired by Hydroxyapatite MicrobeadsCHINESE JOURNAL OF CHEMISTRY, Issue 6 2010Xiang Wang Abstract An approach for the sensitive and selective determination of Ag+, Cu2+ and Hg2+ ions was developed based on the fluorescence quenching of mercaptopropionic acid (MPA) capped CdTe quantum dots in the existence of hydroxyapatite (HAP) nanoribbon spherulites. Among various metal ions investigated, it was found that the fluorescence of CdTe QDs was only sensitive to Ag+, Cu2+ and Hg2+ ions. The addition of HAP into the CdTe system could bring forward a sensitivity improvement of about 1 to 2 orders of magnitude in the detection of Ag+ and Cu2+ compared with the plain CdTe system without the existence of HAP; while there was no sensitization effect for Hg2+. Under optimal conditions, the detection limits for Ag+, Cu2+ and Hg2+ were 20, 56 and 3.0 nmol·L,1, respectively, and the linear ranges were 0.02,50, 0.056,54 and 0.003,2.4 µmol·L,1, respectively. Mechanisms of both QDs fluorescence quenching by metal ions and the sensitization effect by HAP were also discussed. [source] | ||||||||||||||||||||||