A new approach to sample preparation for the determination of trace metals in petroleum source rocks

The dissolution and extraction of petroleum source rocks using a nonionic surfactant to determine their trace metal (V, Ni, Co, Mn, and Mo) content with the assistance of microwave irradiation were investigated and the conditions for obtaining the optimum yield were determined. A complementary microwave-assisted acid dissolution method was also optimized. The results showed that the temperature and time have significant effects on yields of the trace metals. Factors such as surfactant concentration and sample/solvent ratio had little influence on the digestion and extraction efficiencies for these metals. The optimum temperature for microwave-assisted nonionic surfactant dissolution of petroleum source rocks for trace metal determination was 200 degrees C and the best yields of the metals were obtained in 40 min. The optimum temperature and time for nonionic surfactant extraction of trace metals from petroleum source rocks were 90 degrees C and 45 min, respectively. The microwave-assisted acid digestion gave optimum yields of the trace metals in 70 min. The new nonionic surfactant digestion and extraction methods showed efficiencies comparable to those afforded by using the acid digestion method for three out of five elements determined in this study, although the recoveries of vanadium and manganese were relatively low, but the reduction of the digestion/extraction time and environmentally friendliness of the new nonionic surfactant based methods are clear advantages. The new method showed a very good reproducibility. The results of this study also show that the microwave-assisted nonionic surfactant digestion method is a good, efficient and better alternative green analytical preparatory technique for the determination of some trace metals in petroleum source rocks.