For an open potential, the effect of accumulation time on the extraction efficiency was examined in the range of 30–420 s with constant stirring speed. The intensity of the peak P1 and peak P2 of PQ generally increased with extraction time until 180 s (Fig. 4). After 180 s, no dramatic increase of the current intensity was observed with additional extraction time. Moreover, long extraction time may result in solvent drop dissolution in water and consequently leads to poor sensitivity and precision. From a comprehensive view, an extraction time of 180 s was selected for subsequent experiments.