GF-AAS Determination of Cr(Ⅵ) Extracted by Artificial Saliva from Ni-Cr Alloy Dental Crown with Separation by Cloud Point Extraction

The Ni-Cr alloy dental crown was soaked in 10 mL of artificial soliva and kept at 37 ℃ for 4 weeks. An aliquot of 2.00 mL was taken from the extract and 0.1 mL of 2 g·L-1 diphenylcarbazide (DPC) solution, 0.6 mL of Triton X-114 (5+95) as well as 0.5 mL of H2SO4(1+1) were added. After diluting to 10 mL with water, the solution was heated at 40 ℃ for 20 min, to have the Cr(Ⅵ) separated in form of its complex with DPC by the cloud point extraction . The viscous Triton X-114 phase was separated from the water phase and diluted to 1 mL with a mixture of HNO3 and methanol (1+99). Chromium(Ⅵ) in this solution was determined by GF-AAS under the prescribed working conditions of the instrument with 10 μL of the sample solution introduced. Linear relationship between values of absorbance and mass concentration of Cr(Ⅵ) was obtained in the range within 5.0 μg·L-1, with detection limit (3s/k) of 0.088 μg·L-1. Test for recovery was made by addition of 1.0 μg·L-1 of standard Cr(Ⅵ) solution to 6 dental crown samples, results of average recovery found was 96%. Precision was tested by analyzing the same dental crown sample for 6 determinations, the value of RSD found was 3.8%.