Spectrophotometric determination of micro-cadmium in water after ionic liquid extraction

A new extraction spectrophotometry for the determination of micro-cadmium was proposed. In Na2B4O7-NaOH buffer medium at pH 10.8, the Cd-Cadion complex formed by 1-(4- nitrobenzophenone)-3-(4-phenylazophenyl)- triazene (Cadion) and Cd2+ could be extracted by little ionic liquid (1-butyl-3-methylimidazole hexafluorophosphate, BmimPF6). After centrifugal separation, the content of cadmium in ionic liquid phase was directly determined by spectrophotometry at maximum absorption wavelength (517 nm). The linear range of this method was 1.0-62.5 ng/mL, the detection limit was 0.22 ng/mL, apparent molar absorptivity was 6.9×105 L·mol-1·cm-1, the enhancement factor was 29.5, and the relative standard deviation (RSD, 50 ng/mL, n=6) was 2.1 %. The proposed method was directly applied to the determination of micro-cadmium in water sample with recoveries of 96.7 %-108.5 %.