Sensitive and selective methods for the determination of cyproheptadine in tablets using N-bromosuccinimide and two dyes

One titrimetric and two spectrophotometric methods are described for the determination of cyproheptadine hydrochloride (CPH) in bulk drug and tablets employing N-bromosuccinimide (NBS) as a brominating agent and two dyes, erioglaucine (EG) and meta-cresol purple (MCP) as auxiliary reagents. In titrimetry, a measured excess of NBS is added to an acidified solution of CPH and the unreacted NBS is determined iodometrically. Spectrophotometry involves the addition of a known excess of NBS to CPH in acid medium followed by estimation of residual NBS by reacting with a fixed amount of either erioglaucin and measuring the absorbance at 540 nm (method A) or meta-cresol purple and measuring the absorbance at 630 nm (method B). Titrimetric procedure is applicable over the range of 1.5-15 mg of CPH, and the reaction stoichiometry is found to be 1: 2 (CPH: NBS). The spectrophotometric methods are applicable over the ranges of 0.1-2.0 μg mL-1 (method A) and 0.4-12 μg mL-1 (method B). The molar absorptivities are calculated to be 1.4 × 105 and 2.2×104 Lmol-1cm-1 for method A and method B, respectively, and the corresponding Sandell sensitivity values are 0.0023 and 0.0141 μg cm-2. The limits of detection are calculated and found to be 0.03 and 0.24 μg mL-1 for method A and method B, respectively with corresponding limits of quantification 0.09 and 0.71. The methods were applied to the assay of CPH in tablets, and the results were compared statistically with those of a reference method.