Stability-indicating high-performance liquid chromatographic assay for oxazepam tablets and capsules

A stability-indicating high-performance liquid chromatographic (HPLC) assay for oxazepam in capsules and tablets was developed. The material was extracted with 2% aqueous methanol and chromatographed on a C18 reverse-phase column, which was eluted with methanol-water-acetic acid (60:40:1). A wavelength of 254 was used for detection. This assay separated oxazepam from all degradation products mentioned in the literature or observed in stress-degraded samples. Degradation products could be detected at the 0.1% level. Degradation of oxazepam to 6-chloro-4-phenyl-2-quinazolinecarboxaldehyde and 2-amino-5-chlorobenzophenone was observed after either acid or base treatment. Acidic conditions also afforded 2'-benzoyl-4'-chloroglyoxanilide and 6-chloro-4-phenyl-2(1H)-quinazolinone.