Use of Folin-Ciocalteu phenol reagent and 3-methyl-2-benzothiazolinone hydrazine hydrochloride in the determination of oxcarbazepine in pharmaceuticals.

Two spectrophotometric methods are proposed for the assay of oxcarbazepine (OXC) in bulk and dosage forms using Folin-Ciocalteu phenol reagent (FCP) and 3-methyl-2-benzothiazolinone hydrazine hydrochloride (MBTH) as reagents. The first method involves addition of FCP reagent to OXC in alkaline medium followed by measurement of absorbance at 760 nm (method A), and the other involves addition of a fixed volume of MBTH after treatment of OXC with ferric chloride and measurement of absorbance at 456 nm (method B). In both methods, the amount of chromogen formed corresponds to the amount of OXC and the measured absorbance was found to increase linearly with the concentration of OXC, which is corroborated by the correlation coefficients of 0.9985 and 0.9984 for method A and B, respectively. The systems obey Beer's law for 5-30 microg mL(-1) and 10-50 microg mL(-1) for methods A and B, respectively. The apparent molar absorptivity was calculated to be 8.06 x 10(3) L mol(-1) cm(-1) and 3.126 x 10(3) L mol(-1) cm(-1) for methods A and B, respectively. The limits of detection (LOD) and limit of quantification (LOQ) were calculated to be 1.6 and 5 microg mL(-1) for method A and 3 and 10 microg mL(-1) for method B. The inter-day and intra-day imprecision of the methods were found to be in the range of 1.1-1.7 and 0.9-1.1% for method A, and 1.1-1.9 and 0.6-0.9% for method B. The accuracy ranged between 98.9-99.7% and 99.3-100.1 for method A and B, respectively. No interference was observed from common pharmaceutical excipients. The methods were successfully applied to the assay of OXC in tablet preparations.