RESUMO
Electrodes for the dopamine (DA) determination in biological samples have been developed with improved selectivity and sensitivity in an excess of ascorbic acid (AA). Negatively charged Ni(II) complex was synthesized and electropolymerized on the glassy carbon electrode to impart the surface with anionic characteristics that could act both as a catalyst and as a discriminating layer against AA based on the electrostatic interaction. Thus prepared electrodes enabled selective determination of DA even in a large excess of AA by differential pulse voltammetry at physiological pH. Linear response was found down to 1.0 x 10(-7) M with 5.0 x 10(-9) M of LOD (Limit of Detection). In a flow injection analysis performed in an amperometric mode, the detection limit was lowered by two orders of magnitude down to 1.0 x 10(-9) M with a linear range of 1.0 x 10(-9) to 1.0 x 10(-6) M. The relative standard deviation was found to be 3.36% from 25 independent measurements for 1.0 x 10(-5) M of DA. Stable oxidation current of DA was observed even after 30 days storage in air. The recoveries of DA in the 100-fold diluted human urine samples were 97.7% for 4 measurements. The rate constant for the DA oxidation was 1.3 x 10(-3) cm s(-1) from hydrodynamic experiments using a rotating disk electrode.
Assuntos
Ácido Ascórbico/análise , Dopamina/análise , Dopamina/química , Níquel/química , Polímeros/química , Ácido Ascórbico/química , Calibragem , Catálise , Eletrodos , Humanos , Concentração de Íons de Hidrogênio , Cinética , Compostos Macrocíclicos/química , Oxirredução , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Eletricidade EstáticaRESUMO
A batch type chemiluminescence (CL) determination of enoxacin is described. In this work, it was observed that enoxacin could enhance the chemiluminescence (CL) emission Ru(phen)3(2+)-Ce(IV) system and this enhancement effect was dependent on the concentration of enoxacin, based on which, CL system was established for the determination of enoxacin. Under the optimum experimental conditions, the linear range and detection limit are 0.6406-64.06 microg/ml and 0.0210 microg/ml, respectively. The R.S.D. is 1.75%. (n = 10). The proposed method has been applied to detect the content of enoxacin in pharmaceutical formulation and human serum with satisfactory results. The possible mechanism of the CL reaction was discussed.
Assuntos
Anti-Infecciosos/análise , Cério/química , Enoxacino/análise , Fenantrolinas/química , Rutênio/química , Anti-Infecciosos/química , Enoxacino/química , Humanos , Cinética , Medições Luminescentes , Estrutura Molecular , Sensibilidade e Especificidade , Ácidos Sulfúricos/química , ComprimidosRESUMO
A method to determine glucose using an optical sensor prepared by entrapping glucose oxidase into silica sol-gel column has been developed. The silica sol-gel film was coated on alumina substrate. The optical sensor is based on the chemiluminescence intensity from the reaction of periodate and hydrogen peroxide in K2CO3 medium. The effect of the ratio of water and alcohol for the preparation of TEOS sol on chemiluminescence intensity was investigated. The effects of pH of enzyme reactor, concentrations of potassium periodate and SDS, and flow rate on the chemiluminescence intensity were studied to find the optimum experimental conditions to determine glucose. The chemiluminescence intensity increased linearly with increasing glucose concentration from 5.0 x 10(-4) M to 1.0 x 10(-7) M and the detection limit was 4.0 x 10(-8) M. Interference effects from some metal ions on chemiluminescence intensity were also investigated.