Spectrophotometric determination of theophylline formulations

Minophylline (theophylline ethanoate of piperazine) and aminophylline (theophylline ethylenediamine) were determined spectrophotometrically in dosage forms without interference from excipients and/or preservatives. A mixture of minophylline, in about 30-fold concentration, with phenobarbital was assayed for both components with good accuracy and high reproducibility.