Belladonna alkaloids and phenobarbital combination pharmaceuticals analysis II: High-performance liquid chromatographic determination of phenobarbital.

A high-performance liquid chromatographic separation is described for the analysis of phenobarbital in combination pharmaceutical dosage forms containing belladonna alkaloids. A mobile phase of 0.003 M tetramethylammonium chloride in water-methanol (3:2, pH 7.4) was used to separate phenobarbital from belladonna alkaloids on an octadecylsilane column in less than 7 min. The column effluent was monitored at 240 nm, which resulted in a detection limit of 6 ng of phenobarbital. The method is applicable to elixirs, tablets, and capsules with no preliminary extraction procedure. Data from the application of the method to commercial products is also presented.