By making use of the enolization property of phenobarbital in alkaline solution, its content in compound belladonna tablets was determined by differential spectrophotometry. The method was accurate, sensitive and rapid. 利用苯巴比妥在碱液中由酮式转变为烯醇式的特性,采用差示分光光度法测定复方颠茄片中苯巴比妥的含量,结果准确、速。