Desenvolvimento de procedimento analítico em fluxo com multicomutação para a determinação espectofotométrica de ácido úrico em urina / Development of a multicommuted flow-based analytical procedure for the spectrophotometric determination of uric acid in urine

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

Mechanization of analytical procedures in clinical analysis brings advantages such as minimization of systematic errors and analysis time. Multicommuted flow systems attain the requirements to mechanization of analytical procedures in a versatile and robust way, minimizing reagent consumption and waste generation, due to the low solution volumes handled by electronically controlled devices, such as solenoid micro-pumps. The pulsed flow characteristic of the micro-pumps and the binary sampling approach improve sample and reagent mixing. Uric acid is the main end product of purine metabolism and its determination in urine shows clinical importance, because its concentration can be related to human organism dysfunctions, such as gout and renal disorders. An analytical procedure employing a flow system with solenoid micro-pumps was developed, aiming the determination of uric acid in urine samples. Cu(II) ions are reduced by uric acid to Cu(I) ions that can be quantified by spectrophotometry in the presence of 2,2´-biquinoline 4,4´-dicarboxylic acid (BCA). Linear analytical response was observed between 10 and 100 µmol L-1 uric acid and the analytical curve corresponds to the equation A=(0.0063±0.0002) CUA + (0.0285±0.0040), r = 0.999, in which CUA is the uric acid concentration in µmol L-1. The detection limit was estimated as 3.0 µmol L-1 (99.7% confidence level; n = 20). The coefficient of variation was estimated in 1.2% with 20 replicates of a 75 µmol L-1 uric acid solution and sampling rate of 150 h-1 was achieved. The main concomitant species does not interfere in uric acid determination in concentrations up to 5-fold higher than that usually found in urine samples. Recoveries from 91 to 112% were estimated and the results for 4 urine samples agreed with those obtained by the commercially available enzymatic kit for determination of uric acid (95% confidence level). The 100-fold sample dilution minimizes sample consumption and matrix effects. A simple system reconfiguration and a re-optimization of volumetric fractions attained on-line sample dilution by zone sampling. Linear response was observed up to 5.0 mmol L-1 uric acid and the analytical curve corresponds to the equation A=(0.105±0.001) CUA+ (0.023±0.003), r = 0.999, in which CUAis the uric acid concentration in mmol L-1. The coefficient of variation, detection limit and sampling frequency were estimated as 1.0%, 0.2 mmol L-1 and 95 h-1, respectively. The results of the analysis of 3 urine samples also agreed with those obtained with the enzymatic procedure at the 95% confidence level

ASSUNTO(S)

uric acid urine urina multicommutation análises clínicas multicomutação Ácido úrico clinical analysis

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