Abstract

The determination of Zn, Cd and Pb in vegetable oil by electrothermal vaporization in combination with inductively coupled plasma mass spectrometry (ETV-ICP-MS) was investigated. An oil emulsion containing 10% v/v vegetable oil, 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 determination of Zn, Cd and Pb. A mixed modifier of Pd, HNO₃ and H₂O₂ was used to improve the sensitivities and peak shapes of the elements studied. Since the sensitivities of the elements studied in vegetable oil emulsion and that of aqueous solution were quite different, the standard addition method and isotope dilution method were used for the determination of Zn, Cd and Pb in selected vegetable oil samples. The influences of instrument operating conditions, modifier selection, emulsion preparation and interferences on the ion signals 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 market. The analytical results of various vegetable oil samples determined by the method of standard additions and isotope dilution agreed satisfactorily. Precision between sample replicates was better than 10% with the ETV-ICP-MS method. Under the optimum operating conditions, the detection limit obtained 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 corresponded to 20, 1 and 2 ng ml⁻¹ for Zn, Cd and Pb, respectively, in the original oil samples.