Spectrofluorometric determination of acetylsalicylic acid, salicylamide, and salicyclic acid as an impurity in pharmaceutical preparations.

Spectrofluorometry, either direct or in combination with a separation technique, provides a sensitive and accurate method for the determination of certain extent fluorescent analgesic drugs and the determination of impurities in many combination preparations. A critical examination of the UV spectra of common analgesics and related compounds indicates that the fluorescence inner filter effect should be negligible below 10(-5) M and that selective excitation and emission wavelengths should minimize interference from other fluorescent species. Fluorometric procedures are presented for the determination of salicylamide, acetylsalicylic acid, and salicylic acid, as an impurity, in preparations containing salicylamide, acetylsalicylic acid, acetaminophen, caffeine, and phenacetin as major constituents. Inner filtering is the limiting factor only for the direct and indirect determination of salicylamide and the direct determination of acetylsalicylic acid. Results of fluorometric determinations compare favorably with other reference methods. Salicylic acid is determined in the 10(-7) M concentration range after separation from salicylamide, acetaminophen, and caffeine.