PARENT SESSION
1F Human and Veterinary drugs in the environment
9:00 AM to 7:00 PM, Monday, 07 May 2001

(M/EH054) DETERMINATION OF p-AMINOPHENOL BY THE REACTION WITH RESORCINOL USING THERMAL LENS SPECTROMETRY IN PARACETAMOL .

Orlova, Natal'ya¹, Evtushenko, Nikolai², Pikhtar', Anatolii², Proskurnin, Mikhail¹, ^{1 2}

ABSTRACT- p-Aminophenol is a harmful substance for a human organism because it increases body temperature and stays for a long time. It appears in environment from the Chemical and pharmaceutical industrial wastes (water and powdered pollutant emission). Moreover, p-aminophenol is a parent material for the production of paracetamol as one of the most produced pharmaceuticals worldwide. This compound is also an intermediate product of the decomposition of paracetamol and its analogs in the human body and during the storage of its medicinal preparations. Thus, p-aminophenol shows both biochemical and environmental hazards, and the determination of its trace amounts is topical. Existing methods for p-aminophenol determination provide only its detection but not determination. Thus, the aim of this work was to develop a procedure of quantitative determination of p-aminophenol using thermal lensing as a highly sensitive photometric technique. As a model system, we selected the determination of p-aminophenol as impurities in paracetamol preparations. The reaction of p-aminophenol with resorcinol in alkaline medium was selected as a determination reaction due to the highest reproducibility at the submicrogram level of reactants. Physicochemical characteristics of the reaction (the component orders, the characteristic rate constant, and the activation energy) were calculated (mostly for the first time), and the reaction mechanism was ascertained compared to existing data. The optimal conditions for photometric determination of p-aminophenol by the reaction in question at the submicrogram level were found. The limit of detection by spectrophotometry is 2 mg/mL. Thermal lensing under these conditions provided the limit of detection of 0.1 mg/mL; thus, a 20-fold increase in the sensitivity was attained. The achieved limit of detection is fivefold lower than the value for the standard procedure for the determination of p-aminophenol with sodium nitroprusside. The procedure was verified by determining p-aminophenol in samples of paracetamol produced by several pharmaceutical companies.

Key words: p-aminophenol, thermal lensing, kinetic determination, paracetamol