A built-in DUIS (ESI, APCI) interface was used operating in ESI mode, a drying gas flow of 10$l min
1
and a nebulizer gas flow of 1.5$l min
1
. The temperatures of the heating block and the desolation line were 200
C and 250
C, respectively. The analysis was carried out in both positive and negative modes; the applied voltage at the capillary was 4500 V and 4500 V, respectively. All the analyses were performed in single ion monitoring mode. All samples were analyzed twice following the aforementioned method. The acquisition, control and data processing were performed using the Lab Solutions version 3.5 software. The robustness evaluation of the method followed the Youden’s test as described by Ahumada and Zamudio (2011a), using the statistical package PASW STATISTICS 18 included in SPSS. The evaluation results showed the method is robust to changes in the methodology; however, changes in the equipment configuration compromise the performance of the method. The application of the method should follow strict equipment conditions in order to obtain reliable results (Ahumada & Zamudio, 2011a).
After quantification in the laboratory, descriptive statistics were calculated for each pesticide. Then, pesticides concentrations were