RP-HPLC-ICP-MS Determination of Chromium(Ⅵ) in Polyvinyl Chloride Plastics

A portion of the ground polyvinyl chloride (PVC) plastics sample (2.500 0 g) was taken and 50 mL of an alkaline extraction solution (containing 20.0 g of NaOH and 30.0 g of Na₂CO₃ per liter) together with 0.5 mL of pH 7.0 phosphate buffer solution, 0.4 g of MgCl₂ (anhydrous), 2 drops of Triton X-100 was added to the sample. The mixture was digested in a microwave oven. The extract was filtered by vacuum suction and the filtrate together with the washing water were collected and mixed, with its pH adjusted to 7.5±0.5 and its volume made up to 100.0 mL with water. The solution, after filtered through 0.45 μm filtering membrane, was used for RP-HPLC-ICP-MS analysis. The reversed phase chromatographic column of XTerra-C₁₈ was selected as stationary phase, and 2 mmol·L^-1 TBA solution (50 mL of CH₃OH was added to 1 L of this solution and its pH was adjusted to 7.0) was used as mobile phase in isogredient elution, with flow rate of 1.0 mL·min^-1. Separation of Cr(Ⅵ) from Cr(Ⅲ) was achieved by the difference of retention timesi.e., 1.732 min for Cr(Ⅲ) and 4.966 min for Cr(Ⅵ) under the condition mentioned above. The interference of multiatomic ions was attained by applying the mode of single He collision reaction in MS determination. Linear relationship between mass concentration of Cr(Ⅵ) in the range of 0.50 to 200 μg·L^-1 and values of respective peak areas was obtained. Detection limit (3S/N) found was 0.10 μg·L^-1. A CRM of PVCRMA 034, with certified value of Cr(Ⅵ) of (9.3±0.9) mg·kg^-1 was analyzed for its Cr(Ⅵ) content by the present method, giving result of Cr(Ⅵ) (9.19 mg·kg^-1), and with RSD (n=6) of 2.2%. Three PVC utensils were analyzed by this method, and using these samples as matrixes, test for recovery was made by standard addition method, giving results in the range of 94.2% to 101%.