NIR spectroscopy to identify and quantify imazapyr in soil

Abstract

The analysis of herbicide residues applied to the soil is commonly conducted by using chromatographic techniques which use organic solvents, are costly and time consuming. Having a simple and inexpensive discriminant method to determine samples with and without herbicide residues would be highly beneficial to lower costs of analysis and save time. The general objective of the present work was to develop such methodology. In particular, the presence of imazapyr was quantified using a near-infrared spectroscopy (NIRS) and a chemometrics approach. The experimental soil for a qualitative experiment of discrimination was Phaeozem with different agricultural managements and the following treatments: dry soil doped with imazapyr, rehydrated soil also doped with the herbicide, and control soil without the chemical. A discriminant algorithm was developed to allow the identification of soils containing imazapyr and those which did not contain the herbicide. The qualitative approach was based on a discriminant partial least squares (DPLS). An accurate identification of 100 percent of the soils containing imazapyr and 98 percent of those which did not contain the pesticide was achieved. Quantification of imazapyr was performed in five soil types (Andosol, Vertisol, Acrisol, Cambisol and Phaeozem) with different concentrations of the herbicide with an equation generated by modified partial least squares (MPLS) regression. As a reference for the above analytical method, a high performance liquid chromatography (HPLC) analysis was performed. The resulting equation had a RSQ of 0.81 and a prediction capacity (RPD) of 2.4. The results showed that with NIR spectroscopy it was possible to discriminate soils that contained imazapyr from those that did not contain the herbicide. This finding allows for a reduction in the number of samples to be evaluated to determine their concentration. Moreover, with this technique it is also possible to estimate the amount of herbicide in the soil with similar results to those accomplished using the reference method (HPLC), but faster and at lower cost.