Application of postcolumn ionization in the high-performance liquid chromatographic analysis of butabarbital sodium elixir.

A sensitive postcolumn ionization high-performance liquid chromatographic (HPLC) method for the quantitative determination of butabarbital sodium in butabarbital sodium elixir is described. The procedure employs a octadecylsilane column chemically bonded to porous silica microparticles. The mobile phase is a mixture of methanol and water (typically 35:65), adjusted to provide separation of butabarbital from two degradation compounds and other formulation ingredients. A buffer (pH 10) added between the column and detector provides for the primary ionization of the barbiturate necessary for optimum UV-detector sensitivity at approximately 240 nm. Determinations are made using the sodium salt; thus the need for extraction of the free base is eliminated. The procedure is linear over the 0.3-0.9-mg/ml concentration range of butabarbital sodium. Reproducibility values for 10 injections of a single reference standard range from 100.2 to 100.8% of theoretical with a mean of 100.5% and a coefficient of variation of 0.23%. An interlaboratory precision study for blind duplicates of one simulated product formulation and two commercial elixirs produced coefficients of variation of 1.4, 1.3, and 1.1%, respectively. Recovery determinations for the drug in simulated product formulations ranged from 98.4 to 99.0%, intralaboratory, and 97.7 to 102.2%, interlaboratory. The HPLC procedure is stability indicating with respect to two decomposition products.