FLOW-INJECTION SPECTROPHOTOMETRIC DETERMINATION OF CRESOL COMPOUNDS IN WATER BY REACTION WITH P-AMINOPHENOL

A spectrophotometric method has been developed for the simultaneous de termination of o-cresol and m-cresol in water by reaction with p-amino phenol (PAP). Three different methodologies have been assayed; (i) bat ch analysis, after reaction in an alkaline medium in the presence of d issolved molecular oxygen as oxidizing agent, (ii) a stopped-flow proc edure, carried out in the presence of KIO4 and (iii) a flow injection method based on the same approach. The batch procedure requires 22 min for the full development of colour with o-cresol and 12 min for m-cre sol. In the stopped-flow mode, using KIO4 and a reaction time of 12 mi n, better sensitivity can be obtained for both compounds and limits of detection of 10 mug l-1 for o-cresol and 30 mug l-1 for m-cresol were found. The flow injection method has a lower sensitivity but permits more than 80 injections per hour. Based on the different maximum absor bance wavelengths obtained for the reaction products of PAP with o-cre sol (614 nm) and m-cresol (632 nm), both compounds can be simultaneous ly determined in water samples and recoveries of 90 to 115% were found in spiked water samples of different types.