Ion-pair Complexometric Determination of Cyproheptadine Hydrochloride Using Bromophenol Blue

Two simple, rapid and inexpensive methods based on spectrophotometry and turbidimetry have been developed for the determination of cyproheptadine hydrochloride (CPH) in pure form and in dosage forms with Bromophenol Blue (BPB) as the reagent. The spectrophotometric method is based on the formation of an ion-pair complex between the drug and BPB in an acidic buffer. The ion-pair complex formed, which has an absorption maximum at 420 nm, is quantitatively extracted into chloroform. The turbidimetric procedure is also based on the formation of the ion-pair complex which will be present in the form of a turbid suspension at controlled pH and ionic strength conditions. The absorbance of the turbid suspension is measured at 650 nm and is correlated to drug concentration. All experimental variables were studied and optimised for both the methods. The calibration graph is linear in the range of 2-12 μg ml for spectrophotometry, and 10-70 μg ml for turbidimetry. Statistical treatment of the experimental results indicated that the methods are precise and accurate. Excipients used as additives in pharmaceutical formulations did not interfere in the proposed procedures. The procedures were successfully applied to the determination of the bulk drug and its pharmaceutical formulations.