Gravimetric and Spectrophotometric Methods for the Determination of Piperazine. Picrolonic vs. Picric Acid

In the present work two new analytical methods, a gravimetric and a spectrophotometric, for the assay of piperazine free base and its soluble salts in the anthelmitic preparation "Oxyuran", are described. Both approaches are based on the quantitative reaction between the diprotonated cationic form of piperazine and the 3-methyl-4-nitro-1-p-nitrophenyl-5-pyrazolone (picrolonic acid), in sulfuric acid medium, leading to its sparingly soluble canary yellow salt. Both methods exhibit satisfactory levels of mean errors 1.2% and 1.7% respectively. The proposed picrolonate gravimetric method constitutes an improvement of the classical picric acid method regarding the accuracy, sensitivity and selectivity. The two gravimetric methods were compared. Good correlation was achieved, r=0.998. The improvement in sensitivity of the new spectrophotometric method is attributed to the high molar extinction coefficient εmax=18.770 mol –1 l cm–1 of the picrolonates at the measuring wavelength range λmax=342–345 nm. Triethanolammonium-picrolonate and piperazine-diacetate were synthetized and standardized during this work.