Determination of phenytoin by modified extraction-gravimetry with a piezoelectric transducer

An extraction-frequencymetric method has been proposed for the determination of phenytoin sodium using a newly developed ring-coated piezoelectric crystal transducer. The sample solution is acidified with HCl and the liberated free phenytoin is extracted with 1,2-dichloroethane. The extract is applied to a ring-coated quartz crystal in nitrogen stream and after 2 min the crystal frequency is measured. The frequency change due to the deposited phenytoin is proportional to the phenytoin sodium content in the range 0.02–1.2 g. The method can be applied to the assay of phenytoin sodium tablets and injections.