Desenvolvimento e validação de um procedimento de preparo de amostra livre de solvente orgânico para determinação de Glifosato e Ampa em grãos de soja

Abstract

In the present work, a sample preparation procedure for the determination of glyphosate and AMPA in soybean grains was performed and validated using ultrapure water as solvent and neutral aluminum oxide (Al2O3) in the preconcentration stage. Initially, the samples were crushed and the analytes extracted with ultrapure water under vortexing. In the preconcentration of the analytes, the extracts were eluted in cartridges filled with Al2O3 that were later washed with successive portions of ultrapure water to eliminate coextracts. The Al2O3 analytes were removed with 0.10 mol L-1 aqueous solution of sodium hydroxide (NaOH) and the pH adjustment of the extracts was performed with sodium hydrogencarbonate (NaHCO3). In the evaluation of the effect of variables such as sample mass and agitation time, a full factorial design was done. The variables evaluated had a significant effect (p ≤ 0,05, Student's t) on glyphosate recovery. The linear working range was 2,50 to 22,5 mg kg-1 , by ion-exchange chromatography with conductivity detector (CTI-DC) and from 15 to 27 mg kg-1 by high performance liquid chromatography with UV/ Visible detector (HPLC-UV/Vis). The accuracy, expressed in terms of percent recovery, was greater than 85% with coefficients of variation (CV) less than 17% for both analytical techniques. The limits of detection and quantification for glyphosate were 1,20 and 5,00 mg kg-1 by CTI-DC and by HPLC-UV/Vis were 6,00 and 16,5 mg kg-1 for glyphosate and 2,60 and 16,5 mg kg-1 for AMPA. These limits are lower than the reference value established by the Codex Alimentarius, which corresponds to 20 mg kg-1 . After validation, the method was applied to two soybean samples (organic and transgenic) and no glyphosate residues were detected in them. The use of ultrapure water and Al2O3 in the proposed procedure provides accuracy and precision similar to the classic sample preparation for the determination of glyphosate in soybean grains, with the advantage of not using toxic organic solvents, which complies with the precepts of green chemistry and reduces analysis costs.