To check the robustness of the method the pH and sampling levels are shown in Table 3. For the pH=1 levels the responses wereobtained in terms of total area of the peaks of the four pesticides andthe CV was calculated (Table 4).The experimental design showed that the pH is not significant atthe 95% confidence level when varied from 5.0 to 1.0 (Fig. 2). The degree of result reproducibility (Table 4) demonstrates the robustness of the method.