Determination of Zn, Cd and Pb in vegetable oil by electrothermal vaporization inductively coupled plasma mass spectrometry

The determination of Zn, Cd and Pb in vegetable oil by electrothermal vapor ization in combination with inductively coupled plasma mass spectrometry (E TV-ICP-MS) was investigated. An oil emulsion containing 10% v/v vegetable o il, 2% v/v Triton X-100, 2%, v/v H2O2 and 0.4%, v/v HNO3 was prepared. This solution was then injected into the ETV-ICP-MS system for the determinatio n of Zn, Cd and Pb. A mixed modifier of Pd, HNO3 and H2O2 was used to impro ve the sensitivities and peak shapes of the elements studied. Since the sen sitivities of the elements studied in vegetable oil emulsion and that of aq ueous solution were quite different, the standard addition method and isoto pe dilution method were used for the determination of Zn, Cd and Pb in sele cted vegetable oil samples. The influences of instrument operating conditio ns, modifier selection, emulsion preparation and interferences on the ion s ignals were reported. This method has been applied to the determination of Zn. Cd and Pb in sweet corn plumule and canola oil purchased from a local m arket. The analytical results of various vegetable oil samples determined b y the method of standard additions and isotope dilution agreed satisfactori ly. Precision between sample replicates was better than 10% with the ETV-IC P-MS method. Under the optimum operating conditions, the detection limit ob tained from the standard addition curve was 2.0, 0.1 and 0.2 ng ml(-1) for Zn. Cd and Pb, respectively, in prepared emulsified solutions, which corres ponded to 20, 1 and 2 ng ml(-1) for Zn, Cd and Pb, respectively, in the ori ginal oil samples.