Evaluation of a Modified QuEChERS Extraction of Multiple Classes of Pesticides from a Rice Paddy Soil by LC-APCI-MS/MS

Abstract

A new method for the determination of clomazone, fipronil, tebuconazole, propiconazole, and azoxystrobin in samples of rice paddy soil is presented. The extraction of the pesticides from soil samples was performed by using a modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. Some extraction conditions such as salt addition, sample acidification, use of buffer, and cleanup step were evaluated. The optimized method dealt with a single extraction of the compounds under study with acidified acetonitrile, followed by the addition of MgSO(4) and NaCl prior to the final determination by liquid chromatography-atmospheric chemical pressure ionization-tandem mass spectrometry. Validation studies were carried out in soil samples. Recoveries of the spiked samples ranged between 70.3 and 120% with relative standard deviation lower than 18.2%. The limits of quantification were between 10 and 50 μg kg(-1). The method was applied to the analysis of real samples of soils where rice is cultivated.

QuEChERS and soil analysis. An Overview.

“…A sample preparation method is needed for the determination of pesticides due to their low concentration levels, different chemical properties of the analytes, and the complexity of soils [8].…”

“…Some of the analysed contaminants were sensitive to light and, thus, in some applications, soils were collected using dark or amber bottles [5,39] or stored away from the light [5,8]. The temperature was considered crucial in some studies, [48] where the authors performed recovery tests to determine the stability of the compounds under the storage conditions.…”

“…Caldas et al [8] published the first study of the extraction of azoxystrobin, clomazone, and tebuconazole from soil samples using this methodology. Other works are related with novel pesticides [31][32][33] such as pyrimorph, pyraclostrobin and diafenthiuron.…”

“…The addition of the proper amounts and combination of salts can be used to control the percentage of water in the organic phase (and vice versa for organic solvent in the water phase). This allows for a certain degree of adjustment in the polarity of the phase [8,51].…”

“…Caldas et al [8] optimized the salt mixture and concluded that the combinations of MgSO 4 and NaCl were more effective for tebuconazole and propiconazole, but for the more polar compounds (clomazone and azoxystrobin), the recoveries decreased more than 20% when 1 g of NaCl was added. Better recovery for fipronil was achieved with the exclusive use of MgSO 4 rather than in combination with NaCl [8].…”