Methods for pesticide analysis

Pesticides are commonly used in agriculture as plant protection agents. But their use can be harmful if uncontrolled. Even if they help plants to grow without pests, they still pose a hazard to human health. This is due to the pesticides’ toxicity and absorption by the plant.

Aside from the reason above, drainage through the ground can bring pesticide residues to the ground water which people use for drinking. Therefore, not only agricultural crops should be tested, but also ground water, fish, milk, and other things subject to human consumption.

To perform a complete pesticide analysis on crops and other samples, it should include following:

  1. Proper sampling: Get enough representative sample
  2. Sample preparation: Homogenization and extraction of complete residue content
  3. Quantification: Obtaining results by using an analytical technique

The most common techniques used for pesticide analysis are Gas Chromatography (GC) and High-Pressure Liquid Chromatography (HPLC). These techniques are using the different bonding properties of substances (which are in the prepared sample mixture) to separate them in the column and bring them separated to the detector for quantification.

Here is how it works. A carrier (which can be gas in GC or liquid solvent in HPLC) brings the prepared sample through the column which is packed with a stationary phase. Different substances come at different times to the detector which then writes signals on the chromatogram in the shape of peaks. Parallel to the sample, an analysis is done with a standard. This contains the targeted pesticide or a mixture of pesticides in known concentrations. The calibration curve we obtain from the analysis with a standard will help us approximate the quantity of a certain substance in the sample.

Aside from GC and HPLC, analysts also use the Enzyme Linked Immunosorbent Assay (ELISA) method. It uses an antibody which is specific to a certain pesticide. A colour-making substance is also used to quantify the pesticide in a prepared sample. Standards, controls, and samples are added in the same microplate along with an enzyme conjugate. After the reaction (if it occurred), the mixture is coloured and measured in an ELISA reader. The result is then obtained from the calibration curve, which is made from the results of standard solutions in the same assay.

Nunes, G. S., Toscano, I. A., & Barceló, D. (1998). Analysis of pesticides in food and environmental samples by enzyme-linked immunosorbent assays. TrAC Trends in Analytical Chemistry, 17(2), 79–87. 

U.S. Department of Health and Human Services • Public Health Service Food and Drug Administration - Pesticide Analytical Manual Volume I