RESUMO
A new electrochemiluminescent (ECL) disposable biosensor for uric acid was manufactured by immobilization in a double-layer design of luminol as a copolymer with 3,3',5,5'-tetramethylbenzidine (TMB) and the enzyme uricase in chitosan on gold screen-printed cells. The good mechanical and improved electroluminescent characteristics of the new copolymer poly(luminol-TMB) make it possible to determine uric acid by measuring the growing ECL emission with the analyte concentration. The combination of enzymatic selectivity with ECL sensitivity results in a disposable analytical device with a linear range for uric acid from 1.5×10(-6) to 1.0×10(-4) M, a limit of detection of 4.4×10(-7) M and a precision of 13.1% (1.0×10(-5) M, n=10) as relative standard deviation. Satisfactory results were obtained for uric acid determination in 24h-urine samples compared to a reference procedure. This uric acid biosensor can be used as a low-cost alternative to conventional methods.
Assuntos
Benzidinas/química , Técnicas Biossensoriais/métodos , Equipamentos Descartáveis , Medições Luminescentes/métodos , Luminol/química , Ácido Úrico/urina , Técnicas Biossensoriais/economia , Técnicas Biossensoriais/instrumentação , Quitosana/química , Eletrodos , Ouro/química , Humanos , Sensibilidade e Especificidade , Fatores de Tempo , Urato Oxidase/química , Urato Oxidase/metabolismoRESUMO
A rapid liquid chromatography-mass spectrometric method for the determination of five nitroimidazoles in water from different sources is described. The extraction procedure was based on HLB solid-phase extraction with acetonitrile followed by an evaporation step. Ternidazol, another nitroimidazole, was used as the internal standard. The liquid chromatographic separation was made on a C18 bonded silica column applying a gradient with an ammonium acetate buffer solution and acetonitrile. Following electrospray ionisation, the protonated molecular ions [M+H]+ were obtained. Quantification for each nitroimidazole was carried out by monitoring its molecular ion. Calibration functions, quantification and detection limits, intra- and inter-day reproducibility and accuracy were estimated. For the confirmatory assay, several fragment ions from each nitroimidazole were obtained and monitored. The method was applied successfully to determine and identify nitroimidazoles in water from different sources at a level of 0.2 microg l(-1).