Mass fragmentographic determination of timolol in human plasma and urine

A mass fragmentographic procedure was developed for measuring quantities of less than 1.0 ng of timolol/ml of plasma or urine. The lower limit of sensitivity was 0.5 ng of timolol maleate/ml of plasma. The unchanged drug was extracted into heptane--4% isopentyl alcohol from alkalinized plasma or urine, together with propranolol hydrochloride as the internal standard. The compounds were subsequently back-extracted into 0.1 N HCl and then into chloroform following adjustment of the acidic phase to an alkaline pH. The chloroform layer was evaporated to dryness, and the compounds were derivatized with N-methyl-N-trimethylsilyltrifluoroacetamide-acetonitrile to form the trimethylsilyl derivatives; these derivatives were quantitated by mass fragmentography. Recovery of timolol added to normal plasma and urine was quantitative and reproducible, and no interfering substances were observed in normal biological samples. After a 20-mg oral dose of timolol maleate, plasma levels of approximately 3.0 ng/ml were observed at 12 hr.