Sensitive and selective methods for the determination of rizatriptan benzoate in pharmaceuticals using N-bromosuccinimide and two dyes

One titrimetric and two spectrophotometric methods are described for the determination of rizatriptan benzoate (RTB) in bulk drugs and in tablets. The methods use N-bromosuccinimide (NBS) as an analytical reagent, janus green (JG) and calmagite (CMG) as auxiliary reagents. All the three methods are indirect in which the unreacted NBS is determined after the reaction between RTB and NBS is judged complete by iodometric back titration (method A) or by reacting with a fixed amount of either janus green (method B) or calmagite (method C) followed by the measurement of absorbance at 620 nm (method B) or 540 nm (method C). Titrimetry allows the determination of 1–10 mg of RTB and follows a reaction stoichiometry of 1:3 (RTB:NBS), whereas spectrophotometric methods are applicable over the concentration ranges of 0.5–8.0 μg ml−1 in method B and 1.5–30.0 μg ml−1 in method C. Method B with a calculated molar absorptivity of 3.03 × 104 L mol−1 cm−1 is the second most sensitive spectrophotometric method ever developed for RTB. The quality control/assurance parameters such as limits of detection (LOD), quantification (LOQ) and Sandelle’s sensitivity values are also reported for the spectrophotometric method. The accuracy and precision of the methods were studied on intra-day and inter-day basis. No interference was observed from common pharmaceutical adjuvants. Statistical comparison of the results with a reference method showed excellent agreement, and indicates no significant difference in accuracy and precision. The reliability of the methods was further ascertained by recovery studies via standard addition procedures.