Determination of Lead Mercury Cadmium and Chromate in Plastics

Plastics sample was digested with HNO3,HCl,HClO4 and H2O2 (also with HF for silica-containing sample).The heating process was performed either in a microwave oven or in a drying oven at 190 ℃.The sample solution obtained was used for the ICP-AES determination of lead,mercury and cadmium.Same and limited amounts of HCl were added,to compensate for the interference of chloride ion to the determination of mercury.CRM′s were analyzed by the proposed method,giving values of contents of Pb,Hg and Cd in consistency with the certified values,and values of RSD′s (n=9) in the range of 0.3%-8.0%.Hexavalent chromium (CrO2-4) was determined on a separate sample by the diphenyl carbazide (DPC)-photometric method.Hexavalent chromium was extracted from the sample by solution mixtures of NaOH+Na2CO3 and K2HPO4+KH2PO4.An aliquot of filtrate from the extract was taken and its Cr(Ⅵ) content determined by the DPC-photometry.Recovery of Cr(Ⅵ) was tested by addition of standard solution of Cr(Ⅵ) to PVC samples,values of av.recovery and av.RSD′s (n=9) found were 95% and 0.35% respectively.Detection limits (3σ) found for Pb,Hg,Cd and Cr(Ⅵ) were 0.011,0.007,0.003 and 0.001 mg·L-1 respectively.