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Optimum Experimental Conditions (optimum + experimental_condition)
Selected AbstractsDNA Determination in the Presence of Copper in Diluted Alkaline Electrolyte by Adsorptive Stripping Voltammetry at the Mercury Film ElectrodeELECTROANALYSIS, Issue 11 2007Augusto, Mardini Farias, Percio Abstract A stripping method for the determination of single-stranded DNA in presence of copper at the submicromolar concentration levels is described. The method is based on controlled adsorptive accumulation of adenine (from acid-treated DNA) at thin-film mercury electrode followed by linear scan voltammetry measurement of the surface species. Optimum experimental conditions were found to be the use of a 5.0×10,3,M NaOH solution, an accumulation potential of ,0.40,V and a scan rate of 200,mV s,1. The response of adenine,copper is linear over the concentration range 50,250,ppb. For an accumulation time of 15,minutes, the detection limit was found to be 4,ppb. The more convenient relation to measuring the ssDNA in presence of metals and nitrogenated bases were also investigated. The utility of the method is demonstrated by the presence of adenosine-triphosphate (ATP) and amino acids. [source] Quantitation of valproic acid in pharmaceutical preparations using dispersive liquid-liquid microextraction followed by gas chromatography-flame ionization detection without prior derivatizationDRUG TESTING AND ANALYSIS, Issue 7 2010Hamid Reza Sobhi Abstract Dispersive liquid-liquid microextraction (DLLME), coupled with gas chromatography-flame ionization detection (GC-FID), has been successfully used for the extraction and determination of valproic acid (VPA) in pharmaceutical preparations. In the developed method, an appropriate mixture of extracting and disperser solvents was rapidly injected into an aqueous sample. Having formed a cloudy solution, the mixture was centrifuged and then the extracting solvent was sedimented at the bottom of a conical test tube. The extract was then injected into a GC system directly, without any further pretreatment. Initially, microextraction efficiency factors were optimized and the optimum experimental conditions found were as follows: tetrachloroethylene (9.0 µL) as extracting solvent; acetone (1.0 mL) as disperser solvent; 5 mL acidic aqueous sample (pH 1) without salt addition. Under the selected conditions, the calibration curve showed linearity in the range of 0.1,5.0 mg/L with regression coefficient corresponding to 0.9998. The limit of detection was found to be 0.05 mg/L. Finally, the method was applied for the determination of VPA in two different pharmaceutical preparations. A reasonable intra-assay (3.9,10.8%, n = 3) and inter-assay (5.6,11.4%, n = 3) precision illustrated the good performance of the analytical procedure. The protocol proved to be rapid and cost-effective for screening purposes. Copyright © 2010 John Wiley & Sons, Ltd. [source] Highly Sensitive Electrogenerated Chemiluminescence Detecting Ranitidine Based On Chemically Modifying Microenvironment of the Chemiluminescence ReactionELECTROANALYSIS, Issue 11 2005Xingwang Zheng Abstract Using a graphite electrode modified with vaseline and NiO, ranitidine showed a strongly ECL enhancing effect for the weak ECL signal of electrooxidation of luminol. Based on this finding, a more sensitive ECL method for ranitidine was firstly proposed. Under the optimum experimental conditions, the ranitidine hydrochloride concentration in the range of 3.0×10,8,9.0×10,6,mol/L was proportional to the enhancing ECL signal and offered a 9×10,9,mol/L detection limit for ranitidine hydrochloride. At the same time, based on the investigation on this ECL reaction mechanism, a new concept, to improve the suitable ECL reaction micro-environment with chemically modified electrode technique for the better analytical performances of ECL analysis was also firstly proposed. [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] Determination of thyreostatics in animal feeds by CE with electrochemical detectorELECTROPHORESIS, Issue 19 2009Dexian Kong Abstract A simple, rapid, reproducible and sensitive method based on CE with electrochemical detector was developed for the simultaneous determination of five thyreostatics including 2-thiouracil (TU), 6-methyl-2-thiouracil (MTU), 6-propyl-2-thiouracil (PTU), 6-phenyl-2-thiouracil (PhTU) and methimazole (TAP) in animal feeds. A home-made wall-jet electrochemical detector with a 300,,m diameter platinum-disk-working electrode was equipped at the end of separation capillary and used to detect oxidation currents of these thyreostatics. Under the optimum experimental conditions, TU, MTU, PTU, PhTU and TAP could be well separated within 15,min at the separation voltage of 16,kV in 20,mmol/L sodium borate buffer (pH 9.2). The detection limits (S/N=3) of the five thyreostatics in animal feeds were found to be 7.6,,g/kg for TAP, 25,,g/kg for PTU, 15,,g/kg for PhTU, 18,,g/kg for TU and 20,,g/kg for MTU by the developed CE with electrochemical detector method coupled with solid-phase extraction sample pretreatment technique. [source] | ||||||||||