Determination of Nine Metal Elements in Oil Samples by Flame Atomic Absorption Spectrometry with Microwave Digestion

To establish an accurate determination method of metal elements in oils, 5 edible oils and 2 gutter oils were chose as raw material, and a new microwave digestion method was established to pretreat oils in this paper. The contents of metals were determined by flame atomic absorption spectrometry. The programs and conditions of microwave digestion were designed and optimized, and finally a new program for microwave digestion containing 5 steps was obtained, which was with a maximum digestion pressure of 35 atm, a maximum temperature of 190 ℃ and a retention time of 20 min. The performances of the established method were investigated and listed as follows: The linear relations of 9 metal elements were good in their concentration ranges, the determination coefficient ranged was from 0.9982 to 0.9994, the limits of detection was ranged from 0.0013 to 0.0122 μg/mL, and the standard recoveries of samples were ranged from 98.94% to 101.45%, RSD≤4% (n=6). The contents of 9 metal elements in 7 oil samples were determined using this method. The results showed that the nutritional elements in 5 edible oils were rich, and the contents of Cr , Cd and Pb were not detected, therefore, estimated preliminary, the nutritional value and safety of the oils were high. However, Cr, Cd and Pb in gutter oils were all detected, and the contents of Pb are far higher than the threshold limit value of national standard, so the gutter oils are not suitable for consumption. These applications showed that the method has many advantages of simple operation and high accuracy, the needs of determination of metal elements in oils can be satisfied.