Determination of Neonicotinoid Insecticides in Environmental Water by the Enrichment of MIL-53 Mixed Matrix Membrane Coupled with High Performance Liquid Chromatography

“The concentration of four neonicotinoid insecticides was detected by Agilent 1100 liquid chromatographic system coupled with DAD detector. HPLC separation was carried out using a ZORBAX SB-C18 column (4.6 × 250 mm, 5 µm) at room temperature. The sample injection volume was 20 µL. DAD absorbance was monitored at 244 nm and 270 nm. The mobile phase was a mixture of methanol and water. Gradient elution conditions were as follows: 0–5 min, isocratic 30% methanol; 10–18 min, isocratic 55% methanol. The flow rate was 0.8 mL min−1. Under these optimum conditions, all studied insecticides were well separated from each other.”

3.5. Analytical Performance of the DME-HPLC Method

Under the optimum extraction conditions, several analytical performance parameters of this established method were evaluated. As listed in Table 1, good linearity was achieved within the concentration ranges of 0.20–15.00 μg L−1 for nitenpyram, 0.04–15.00 μg L−1 for imidacloprid and thiacloprid, and 0.05–15.00 μg L−1 for acetamiprid. Calibration curves were obtained by plotting the peak areas (y) of neonicotinoid insecticides versus their concentrations (x). The obtained correlation coefficients (r2) is between 0.990–0.996. The limits of detection (LODs) and the limits of quantitation (LOQs) were calculated based on analyte signal to background noise ratio of 3 and 10, respectively. As seen in Table 1, the LODs and LOQs of four neonicotinoid insecticides were 0.013–0.064 μg L−1 and 0.038–0.190 μg L−1, respectively.
Table 1. Regression equation, linear range, correlation coefficient (r2) and method detection limit, and limit of quantification of four neonicotinoid insecticides.
Analyte Regression Equation a Correlation Coefficient (r2) Linear Range (µg L−1) LOD (µg L−1) LOQ (µg L−1)
Nitenpyram y = 1.764x − 0.6893 0.9937 0.20–15.00 0.064 0.190
Imidacloprid y = 12.801x − 1.0903 0.9957 0.04–15.00 0.013 0.038
Acetamiprid y = 14.542x + 0.0519 0.9960 0.05–15.00 0.017 0.050
Thiacloprid y = 12.638x − 2.8553 0.9901 0.04–15.00 0.014 0.041
a x means concentration of neonicotinoid insecticides (µg L−1), y means peak area.
The relative standard deviations (RSDs) of peak areas at three spiked concentration levels (0.5, 5 and 10 μg L−1) were used to evaluate the precision of the proposed method. As listed in Table 2, the spiked recoveries ranged from 78.72% to 119.68%. The intra-day (n = 6) and inter-day (n = 6) RSDs were in the range of 3.07–12.78% and 3.43–13.12%, respectively.

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