Computer assisted optimization of a flow-injection method for the assay of promethazine, chlorpromazine and trimeprazine in drug formulations.

A simple, accurate and fast method for the determination of promethazine, chlorpromazine and trimeprazine neuroleptics in drug formulations by flow injection spectrophotometric detection was developed. The method was based on the oxidation of the drug with potassium dichromate in sulphuric acid media. Optimum conditions were obtained by using the modified simplex computer programme. A 110-mul sample volume was taken as reasonable for all the compounds. The optimum conditions reached were 76-cm coil length, 6.00 ml/min flow rate, 3.10M sulphuric acid and 0.00167M dichromate for promethazine; 94-cm coil length, 5.00 ml/min flow rate, 1.48M sulphuric acid and 0.00185M dichromate for chlorpromethazine and 80-cm coil length, 6.00 ml/min flow rate, 3.44M sulphuric acid and 0.000500M dichromate for trimeprazine. High sample throughput of at least 200 samples per hour was obtained for all compounds. Acceptable relative standard deviations in the range +/-0.4-0.9%, and good accuracy in the range 99.5-99.9% were attained when the method was statistically compared with the BP method and when applied to proprietary drugs, without suffering interferences.