Effect of components of the matrix in pesticide analysis by gas chromatography / Efeito de componentes da matriz na análise de agrotóxicos por cromatografia gasosa

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

This work aimed to systematically study the matrix effect on the measurement of pesticides chlorpyrifos, λ−cyhalothrin, cypermethrin and deltamethrin by gas chromatography with electron capture detector. The matrix effect is attributed to the presence of co-extractives in the organic phase during extraction. In this work, the phenomenon matrix effect is described in detail in a review discussing qualitative and quantitative aspects as well as techniques used to minimize it. Also reports results that quantify co-extractive interference with the chromatographic response of the four pesticides. There was a positive matrix effect after GC saturation with multiple injections of tomato organic extracts for the four pesticides. It was also found that the longer the retention time, the greater the matrix effect (10% for chlorpyrifos, 103% for λ-cyhalothrin, 162% for cypermethrin and 300% for deltamethrin), and that the internal standard minimizes the effect, but not eliminate it. An in-depth study of chlorpyrifos and deltamethrin adsorption on the injector and chromatography column was carried out. These were the pesticides that showed the lowest and greatest matrix effect, respectively, in previous studies. The capacity of chlorpyrifos and deltamethrin being adsorbed in the injector and chromatography column was assessed by plotting three isotherms with the injector at 310, 280 and 250C and modifying the heating rate of the column to 10 and 30 C min-1. For a range of concentrations between 5 and 500 g L-1, the results showed that the higher the injector temperature (310 C) and the lower the heating rate of the chromatography column (10 C min-1), the lower is the pesticide adsorption in the chromatography system. The results also showed that deltamethrin may present characteristics of protective analyte, reducing chlorpyrifos adsorption in the analysis of analyte standard solutions in pure solvent. A simple and practical method for identification and quantification of chlorpyrifos, λ-cyhalothrin, deltamethrin and cypermethrin in honey samples was also optimized and validated. The method is based on liquid-liquid extraction and purification at low temperature using the extractor mixture acetonitrile:ethyl acetate (6.5 mL: 1.5 mL). An additional clean-up step was performed with 2.0 g of florisil before analysis by gas chromatography. The efficiency of the technique was shown to be satisfactory (>85%) and chromatographic response was linear for all pesticides in the range 0033 - 0.17 g g-1, with correlation coefficients above 0.99. Limits of detection and quantification were below 0.017 and 0033 g g-1 respectively. The proposed method was applied to 11 honey samples and detected residues of chlorpyrifos and λ-cyhalothrin in two samples, at concentrations below the MRLs established for food products. The presence of these compounds was confirmed by mass spectrometry in the SIM mode (GC-MS-SIM). Finally, the influence of chemical constituents of nine matrices (honey, tomatoes, milk, apples, soil, potatoes, liver, rump meat and water) on the quantification of the pesticides by GC-ECD was studied. With this purpose, organic extracts of each matrix were obtained from LLE-LTP or SLE-LTP and used to saturate the chromatography system. Standard pesticide solutions were injected before and after GC saturation with extracts of each matrix. Variation of chromatographic responses was evaluated by principal component analysis (PCA) and hierarchical cluster analysis (HCA). Results showed that the constituents of tomato organic extracts accounted for the greatest matrix effect on pyrethroid chromatographic responses in GC-ECD analyses (100 to 300%). This was confirmed by principal component analysis, which evaluated the distance of the response of tomato organic extracts from the other responses. Furthermore, the saturation of the chromatography system with extracts of water, soil, apple and honey decreased pyrethroid chromatographic responses.

ASSUNTO(S)

quimica analitica gas chromatography pesticides agrotóxicos efeito de matriz matrix effect cromatografia gasosa

ACESSO AO ARTIGO

Documentos Relacionados