Comparison of capillary electrophoresis and reversed-phase liquid chromatography methodologies for determination of diazepam in pharmaceutical tablets

Two novel analytical methodologies using capillary electrophoresis (CE) and reversed-phase high-performance liquid chromatography (RP-HPLC) for the determination of diazepam in commercial and simulated tablet formulations were developed and compared. The CE analysis was carried out in a bare fused-silica capillary with 75 μm i.d. and total length of 50 cm (28 cm to the detector) with a buffer solution containing 20 mmol L−1 sodium tetraborate and 20 mmol L−1 sodium dodecylsulfate (SDS), pH 9.23. The applied voltage was 20 kV and bromazepam was used as internal standard (IS). The RP-HPLC analysis was carried out in a LiChrospher® 100 RP-18 (5 μm) column with a mobile phase constituted of methanol, acetonitrile and water (45:25:30) with a flow rate of 0.8 mL/min, using acetaminophen as IS. In both cases, detection was carried out by ultraviolet (UV) absorption at 242 nm. Under the optimized conditions, the CE retention times for the standard diazepam and bromazepam (IS) were 4.08 and 3.43 min, respectively, and the retention times of the RP-HPLC analysis for the standard diazepam and acetaminophen (IS) were 4.86 and 1.58 min, respectively. The resolution and efficiency for CE were 7.4 and 1.18 × 105 plates/m and for RP-HPLC, 7.5 and 1.76 × 104 plates/m. Analytical curves of peak area versus concentration presented correlation coefficients of 0.9996 for CE and 0.9994 for RP-HPLC. The limits of detection (LOD) and quantitation (LOQ) were 4.24 and 12.85 μg/mL for CE and 1.44 and 4.36 μg/mL for RP-HPLC. Relative standard deviations (R.S.D.) were 1.62 and 0.98% for CE and RP-HPLC, respectively. The percentage recovery determined with CE was 100.27 ± 1.25 and with RP-HPLC was 101.12 ± 2.48. Although both methodologies were shown to be suitable for the determination of diazepam in tablets, performing in a similar manner with regards to several aspects (linearity, recovery and specificity), CE provided a faster analysis and column efficiency whereas RP-HPLC presented a superior repeatability and sensitivity.