Abstract
Microwave plasma atomic emission spectroscopy (MP-AES), which uses nitrogen as plasma gas is an interesting development in analytical science sine the running cost can be remarkably reduced in comparison to the inductively coupled argon plasma. However, the determination of trace elements in edible oils needs very sensitive instrumental techniques such as ICP-OES or ICP-MS because of the low concentrations of trace elements in the samples. Furthermore, the high organic content of oil matrix increases the possibility of interference during analysis. In order to figure out these problems, we focused on improving the pretreatment of edible oils in this study. The research was divided into two parts: microwave acid digestion (MAD) and liquid-liquid extraction (LLE). For MAD, edible oil was digested by different reagent conditions. The optimized condition：0.3 mL oil sample + 8 mL con. HNO3 was based on the results of UV-Vis and MP-AES. We also verified the assurance of this method by analyzing certified reference material (recovery: 80~111%). In the second section, ultrasound-assisted liquid–liquid extraction was used to pretreatment oil samples. The experimental parameters: sonication temperature, sonication time and centrifugation time were optimized to improve the sensitivity and detect the metals in minimum time. The proposed procedure of combining MP-AES can be regarded as a new procedure for the determination of metals in various edible oils (olive oil, sunflower oil, grape seed oil, soybean oil, rice bran oil, canola oil and sesame oil). For the purpose of detecting tendencies in the samples of the same type of oil, principal components analysis was used and the results for LLE MP-AES were compared with MAD ICP-MS.