In vitro monitoring of picogram levels of captopril in human urine using flow injection chemiluminescence with immobilized reagent technique

A flow-injection procedure for detection of captopril using a Co2+ -captopril complex formed on line based enhancement of luminol and dissolved oxygen chemiluminescence is described. The chemiluminescence reagents, luminol and Co2+ , were both immobilized on ion exchange resin in the flow injection system. When captopril solution flowed through the immobilized Co2+ column, the Co2+ -captopril (1:2) complex formed on line could greatly enhanced the chemiluminescence intensity generated from the reaction between luminol and dissolved oxygen. The increment of chemiluminescence emission was correlated with the captopril concentration in the range from 7 to 1000 pg mL(-1) , and the detection limit was 2 pg mL(-1) (3 sigma). One analysis cycle, including sampling and washing, could be accomplished in 0.5 min with relative standard deviations of less than 3.0% (n=11). The proposed method was applied directly in the assay of human urine without any pretreatment and it was found that the captopril concentration reached its maximum after being administrated orally for 1.5 hours, with the mean excretion ratio in 6.5 hours of 54.3% in the body of volunteers. The possible chemiluminescence mechanism was discussed.