A Simple Enzymatic Technique for Determination of Monocrotophos Residues in Tender Coconut Water

A simple and rapid enzymatic technique for determination of monocrotophos residues in tender coconut water was developed by modifying Ellmanʹs method, which was originally developed for measuring the activity of acetylcholinesterase enzyme (AChe, EC.3.1.1.7.). Coconut water from fresh tender coconut was adjusted to pH 8.0, filtered through Whatman No. 1 filter paper and used to inhibit the activity of AChe present in horse serum. The extent of enzyme activity inhibited by contaminated or spiked coconut water, in comparison to standard monocrotophos solution, was used for quantifying its residues in tender coconut water. Comparative evaluation of reaction kinetics and inhibition pattern of AChe in standard monocrotophos solution and spiked coconut water showed that the enzyme reaction curves were linear up to about 4 - 8 min of reaction depending upon the concentration of monocrotophos in either case. The reaction completion times varied from 20 - 25 and 22 - 26 min for the standard monocrotophos solution and the spiked coconut water, respectively. The extent of enzyme inhibition was significantly (p<0.01) greater for the standard solution than that for the spiked coconut water at the same concentration level. Limit of detection and time of determination of monocrotophos residue by the enzymatic technique were 0.25 - 0.50 (mu)g and 1 has compared to 1 - 2(mu)g and 2 - 3 h, 0.005 - 0.010 (mu)g and 2-3 h and 0.0005 - 0.0010 (mu)g and 2-3 h in TLC, GC with TID detection and HPLC with UV detection, respectively.