Determination of chlorpyrifos in environmental water samples by dispersive liquid-liquid microextraction with solidification of a floating organic drop followed by gas chromatography with flame photometry detection

Dispersive liquid-liquid microextraction with solidification of a floating organic drop (DLLME-SFO) followed by gas chromatography with flame photometry detection (GC-FPD) has been adopted and improved for determining chlorpyrifos in environmental water samples. A mixture of 1.5 mL of methanol (disperser solvent) and 40 mu L of 1-dodecanol (extraction solvent) was quickly injected into 25 mL of a water sample with a liquid-transferring device. After five minutes, 0.5 g of sodium chloride was added into the aqueous solution and the sample vial was shaken by hand. Another five minutes later, the sample was centrifugated at 3400 rpm for 3 min, and then the centrifugal tube was placed in an ice bath. When the extraction solvent floating on the top of the aqueous solution had solidified, it was transferred into another vial and diluted with 60 mu L of ethyl acetate. The extraction recovery (ER) and the enrichment factor (EF) were 79.02% and 232.42, respectively. The limit of detection (LOD) (S/N = 3) was 0.02 mu g L-1, the linear range was 0.05-4 mu g L-1, the relative standard deviation (RSD) was in the range of 3.93-7.29% and the recoveries of spiked samples ranged from 84.34% to 110.20%.