Time-resolved chemiluminescence: a novel tool for improved emission sequence in stopped-flow analysis Application to a kinetic study of the oxidation of naloxone

A simple, inexpensive assembly for flow analysis coupled with chemiluminescence detection and based on stopped-flow chemistry is reported. A 22 bit analogue-to-digital converter that acquires analogue signals at -10 and +10 V and allows the power supply to the peristaltic pump to be interrupted is used in the time-resolved chemiluminescence manifold to ensure rapid, efficient mixing of chemiluminescent reagent and sample immediately before reaching the detector; this results in high precision and detectability, particularly with fast, short-lived emissions. The proposed system also exhibits a high throughput (45 samples/h) and a low reagent consumption. The system was validated by using it to study the chemiluminescent oxidation of naloxone by potassium permanganate in a phosphoric acid medium. The optimum conditions for chemiluminescence emission were established. The emission resulting from the oxidation of naloxone by permanganate ion in the stopped-flow mode revealed four analysis modes. Therefore, the conditions were optimised in terms of four quantitative parameters adjustable via software settings, namely: the maximum emission intensity, total emission, rate of the light-development reaction and rate of the light-decay reaction. Linear calibration graphs were obtained with each measurement parameter with detection limits ranging from 0.15 to 0.22 (mu)g mL^-1 and R.S.D. values (n=10) of 0.07–0.18 at a 3.0 (mu)g mL^-1 concentration level. The method was applied to the determination of naloxone in pharmaceutical preparations.