OPTIMISED CALIBRATION PROCEDURE FOR BIOANALYTICAL DETERMINATION OF ORGANOPHOSPHATE PESTICIDES iN apple juices BY IMMOBILISED AChE
Klavdija Mežnar, Boris Pihlar
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana, Slovenia
Biotechnical Faculty, Department of Food Science and Technology, University of Ljubljana, Jamnikarjeva 101, SI-1000 Ljubljana, Slovania
Nova Gorica Polytechnic, School of Enviromental Sciences, P.O.Box 301, SI-5001 Nova Gorica, Slovenia
The bioanalytical method, based on flow injection analysis (FIA), was optimised for detection of organophosphate pesticides in apple juices. The matrix effects (pH value of the sample and presence of alkaline and alkaline earth metal ions) were studied. The activity of acetycholinesterase (AChE), immobilised on controlled porosity glass, was found to be strongly dependent on the pH value of the mobile phase, which also influences the enzyme inhibition. The optimal pH value was found to be at 7.4. The presence of 0.1 M alkaline and alkaline earth metal ions decreased the enzyme activity for about 20%. In addition, a notable effect on the process of enzyme inhibition by pesticide paraoxon, which was chosen as a model organophosphate pesticide, was observed already when the concentrations of investigated ions were between 0.001 M and 0.01 M. For calibration purposes the standard solutions of paraoxon therefore need to be prepared with the addition of metal ions in concentrations corresponding to those present in investigated apple juice and the pH value of apple juice adjusted to 7.4 by the addition of Tris buffer.