Studies On Rapid Detection Of Pesticide Residues In Some Fruits And Vegetables By Phytoesterase Inhibition And Potentiometry

Organophosphorus and carbamate pesticides are two common pesticides which are often regarded as important hazard substances in food safety inspection due to their high acute toxicity to human and animals. Some virulent kinds of organophosphorus and carbamate pesticides are still used to vegetables and fruits in some regions although they are forbidden by the government. The toxicosis incidents of human and animals resulted from taking food which contains high level of pesticide residues are happened usually.At present, GC is a common method for detecting organophosphorus and N-methylcarbamate pesticides residues, which has high veracity and sensitivity, but it's too expensive and complex to use as a method for fieldwork detection. There are many researches on the methods of rapid detection as well, especially the enzyme inhibition method. This article has compared four kinds of enzyme inhibition methods, established the Phytoesterase Potentiometry on-the-spot method, and has studied the influence factors of on-the-spot method. The results are as follows:(1) Compared the Phytoesterase potentiometry, Colorimetry and Immobilized Phytoesterase: In six kinds of pesticides which are detected, The C.V. of six pesticides to be detected by potentiometry were between 2.34 and 3.56 with LDC between 0.008and 0.156, which are all better than other two examination methods.(2) The optimization of potentiometry: the detection enzyme is the Phytoesterase which was prepared by our laboratory. Take 4mL 50 times of dilutions of the original enzyme fluids to looks, followed by adding 2ml pesticides and 2ml water, and then inhibit at 25℃water bath for 15 minutes. Then add 1.4mL of 0.5%α-Naphthyl acetate, measuring the pH values (pH1) ,and then react at 40℃for 30min, at 25℃for 10 minutes, measuring the pH values (pH2) . Commutate theΔpH values, make standard work curve with the pesticide concentration vs the enzyme inhibition ratio. The results will be calculated by the inhibition ratio of the samples.(3) Compared the Phytoesterase potentiometry and AchE colorimetry: It is indicated that the inhibitions to the two enzymes of the Phytoesterase potentiometry and AchE colorimetry are similar in the same detection concentration, the C.V s and LDC are similar.(4) Studied the influence factors of the fruits and vegetables preparation and established the method of sample preparation: the best supersonic time is 8min, the best extraction solvent is methyl alcohol : acetone : ethyl acetate (1:2:3). The sample refining is added by 20ml extraction solvent in supersonic to withdraw 8 minutes.(5) Studied on recovery rates of pesticides of each kind of extraction solvent. The recovery rates of the Phytoesterase potentiometry to detect the pesticides were between 89% and 98%. The result shows that the method has higher recovery rate and better accuracy, which accord with the requirements of pesticide residue assay.(6) Studied on the Influence factors of On-the-spot method: it is definite that vacuum freezing concentration is the best processing method to preserve fruits and vegetables, and it determined the relation of the inhibition rates and the pesticides toxic. The inhibition rates which are bigger than 70% is virulent, between 50% and 70% is middle poisonous, between 30% and 50% is low poisonous, between 10% and 30% is the lower poisonous, lower than 10% is nonpoisonous.(7) The flow of On-the-spot method:Take tomato detection as the example: firstly, partial tomato are refined. Add 5g tomato refining fluid in one 100mL test tube, simultaneously adding 0.463g tomato refining fluid without pesticides residues by the proportion to the other one test tube, as the control sample. Then add 20mL extraction solvents methyl alcohol + ethyl acetate + acetone (1:2:3) to the two tubes separately. Then, two test samples are extracted with supersonic. In the supersonic extractor, the water surface is higher than the test tubes. At last, the two test tubes are taken out after 8min.8ml en2yme fluids are added separately in two test tubes. The first test tube is added 0.5ml control sample, while the second test tube is added 0.5ml sample extracts. Then the two tubes enzyme are inhibited at 15℃water base for 10min. And then add 1.4ml 0.5%α-Naphthyl acetate, measuring the pH values(pH1). Then react at 40℃for 30min, followed by reacting at 25℃for 10 minutes, measuring the pH values (pH2) . Commutate the inhibition rates according to inhibition rates formula, Then contrast pesticide residue toxicity according to result (6).