Studies on protein precipitants for identification and determination of paraquat in biological materials.

Abstract

For simple and quick determination of paraquat [PQ] in biological material, availability of supernatant obtained by protein precipitation directly for the colorimetric determination after reduction of PQ with alkaline sodium hydrosulfite was examined. Interference of four protein precipitants commonly used were tested for alkaline sodium hydrosulfite reduction of PQ. The characteristic spectrum of reduced form of PQ changed in the presence of trichloracetic acid or perchloric acid. Tungstic acid, under acidic condition, reacted with alkaline sodium hydrosulfite and developed dark blue colour. When sample was first adjusted to alkaline pH by NaOH solution and then crystaline sodium hydrosulfite was added, formation of tungstic blue was, however, not seen. Use of these three protein precipitants might, therefore, lead to misunderstanding in PQ determination and should be avoided. In contrast, sulfosalicylic acid showed no interference in the following determination of PQ and PQ added to homogenate was recovered quantitatibly. Chosing a suitable precipitant, sulfosalicylic acid, post protein precipitate supernatant was available for the determination of PQ directly in tissue homogenate.