The Reliability of Pesticide Determinations Using near Infrared Spectroscopy and the Dry-Extract System for Infrared (DESIR) Technique

Abstract

In a previous article, a pesticide determination system using near infrared (NIR) spectroscopy and the dry-extract system for infrared (DESIR) technique had been developed. In order to evaluate system reliability, a number of tests had been conducted. To reduce time and labour needed for pesticide assays by gas chromatography, artificial solutions of each pesticide in acetone were used in place of sample extract that was used in the previous article. Effects of several factors, such as chemical structure, interference of another reagent in the solution and sample presentation, on the system accuracy were evaluated. A tentative collaborative study was conducted to evaluate the possibility of large scale utilisation. To test the influence of chemical structure, three pesticides— acephate, dichlofluanid and tetrachloro-isophthalonitrile (TPN)—having different numbers of functional groups with strong dipole moment were used. From the range of 0 ppm to 50 ppm active ingredient in acetone, the SEPs obtained were 2.1, 5.3 and 9.3 ppm for acephate, dichlofluanid and TPN, respectively. These results corresponded to the number of strong dipole moment groups in the chemical structure which were four for acephate, two for dichlofluanid and none for TPN. In the case where two kinds of pesticide were presented in the system, the SEP became larger compared to the single pesticide results. The degree of interference differed depending on the relative absorptivity between the target pesticide and the interference. Using the system developed and acephate solution, a tentative collaborative study was conducted using three laboratories and four technicians. The almost similar SEPs of 2.8, 2.8, 3.0 and 2.5 ppm were obtained by the four technicians, indicating that even if the NIR instruments used and the degree of professional skill differed between technicians, satisfactory results could be obtained after a few hours of training and a proper bias correction. Finally, to simplify the system, three kinds of sample presentation were used to develop a calibration equation for acephate. The SEPs obtained differed only minutely. It could be concluded that when using NIR analysis the operator may choose between the highly precise system which requires more time and labour because of the sample preparation involved or a slightly less precise system with simple sample presentation. Based on the Japanese pesticide control level, the developed system could be used for the monitoring of some pesticides in fruits and vegetables.