Development of multi-response optimization and quadratic calibration curve for determination of ten pesticides in complex sample matrices using QuEChERS dispersive liquid-liquid microextraction followed by gas chromatography.

In this study, QuEChERS combined with dispersive liquid-liquid microextraction is developed for extraction of ten pesticides in complex sample matrices of water and milk. In this regard, effective factors of proposed extraction technique combined with gas chromatography with flame ionization detector were designed, modeled, and optimized using central composite design, multiple linear regression, and Nelder-Mead simplex optimization. Later, univariate calibration model for ten pesticides was developed in concentration range of 0.5-100 ng/mL. Surprisingly, quadratic calibration behavior was observed for some of the pesticides. In this regard, Mandel's test was used for evaluating linearity and types of calibration equation. Finally, four pesticides followed linear calibration curve with sensitivity (0.23-0.66 mL/ng), analytical sensitivity (0.20-0.32), regression coefficient (0.988-0.995), limit of detection (0.39-1.83 ng/mL), and limit of quantitation (1.30-6.10 ng/mL) and six of them followed quadratic calibration curve with sensitivity (0.18-0.93 mL/ng), analytical sensitivity (0.25-0.86), regression coefficient (0.944-0.999), limit of detection (0.59-1.92 ng/mL), and limit of quantitation (1.96-6.40 ng/mL). The calculated limits of detection were below the maximum residue limits according to European Union pesticides database of European Commission. Finally, the proposed analytical method was used for determination of ten pesticides in water and milk samples.