Sensitive determination of captopril by flow injection analysis with chemiluminescence detection based on the enhancement of the luminol reaction

This work reports a novel flow injection (FI) method for the determination of captopril, 1-[(2S)-3-mercapto-2-methyl-propionyl]-L-proline (CPL), based on the enhancement CPL affords on the chemiluminescence (CL) reaction between luminol and hydrogen peroxide. For this purpose alkaline luminol and hydrogen peroxide solutions were mixed online, the sample containing CPL was injected into an aqueous carrier stream. mixed with the luminol-hydrogen peroxide stream and pumped into a glass flow cell positioned in front of a photomultiplier tube (PMT). The increase in the CL intensity was recorded in the form of FI peaks, the height of which was related to the CPL mass concentration in the sample. Different chemical and instrumental parameters affecting the CL response were investigated. Under the selected conditions, the log-log calibration curve was linear in the range 5-5000 mug l(-1) of CPL, the limit of detection was 2 mug l(-1) (at the 3sigma level), the R.S.D., s(tau) was 3.1% at the 100 mug l(-1) level (n = 8) and the sampling rate was 180 injections h(-1). The method was applied to the determination of CPL in pharmaceutical formulations with recoveries in the range 100+/-3%. (C) 2002 Elsevier Science B.V. All rights reserved.