Study On The Dispersive Liquid-Liquid Microextraction Method For The Spectrophotometric Determination Of Mercury And Nickel

Dispersive liquid-liquid microextraction (DLLME) is a simple, rapid sample preparation technique. DLLME technique combined with spectrophotometry for the preconcentration and determination of mercury and nickel in food samples was developed.For the DLLME of mercury, chloroform, ethanol, and dithizone were used as extraction solvent, disperser solvent and chelating agent, respectively. The complex formed after the complexation reaction of mercury and dithizone was extracted by DLLME. Some important DLLME parameters were investigated in detail. The optimal conditions were: volume of chloroform,75μL; volume of ethanol,1.8mL; pH,2.0; concentration of dithizone,4.5μmol·L-1; centrifugation rate,3500r-min-1. The deposited phase after DLLME was diluted with acetone and then determined at495nm. Under the optimized conditions, the calibration graph for mercury was linear from10to200μg·L-1. The limit of detection was3μg·L-1and the relative standard deviation (n=7) was4.3%. Interferences such as Cd2+、Cu2+、Ni2+and Pb2+could be eliminated by EDTA-Na2. The proposed method was successfully applied to the determination of mercury in fish and tea-leaves with recoveries between96.2%and103.0%.For the DLLME of nickel, tetrachloromethane, ethanol and2-(5-Bromo-2-pyridylazo)-5-diethylamino phenol (Br-PADAP) were used as extraction solvent, disperser solvent and chelating agent, respectively. The complex formed after the complexation reaction of nickel and Br-PADAP was extracted by DLLME. Some important DLLME parameters were investigated in detail. The optimal conditions were:volume of tetrachloromethane,100μL; volume of ethanol,1.2mL; pH,5.5; concentration of Br-PADAP,3.0μmol·L centrifugation rate,3500r·min-1. The deposited phase after DLLME was diluted with ethanol and then determined at565nm. Under the optimized conditions, the calibration graph for nickel was linear from1to30μg·L-1. The limit of detection was0.3μg·L-1and the relative standard deviation(n=7) was3.2%. Interferences such as Fe3+and Cu2+could be eliminated by acetylacetone and thiourea, respectively. The proposed method was successfully applied to the determination of nickel in water, fish and coffee with recoveries between96.0%and103.0%.