Microwave Acid Digestion of Crude Oil Samples Using a New High Performance Vessel

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Microwave digestion is the preferred sample preparation technique for crude oil samples prior to heavy metals analysis.  Samples are digested in a concentrated acid matrix in a closed vessel and heated in a commercial microwave digestion oven where the speed of thermal decomposition of the sample and the solubility of metals are increased. Once these metals are in solution, their concentration can be quantified through spectroscopic techniques. The MARS 6 acid digestion process routinely cuts the time of sample preparation by 50 – 75% as compared to hot plates and hot block.



The analysis of metals in crude oil prior to refining is of vital importance to the oil refining industry. V and Ni, for example, can act as catalyst poisons affecting the distillation process while toxic elements such as As and Se must be monitored due to environmental concerns. Traditionally, microwave digestion systems have been limited to smaller sample sizes due to the amount of NOx gases produced in the digestion process. This application note will focus on the use of the CEM MARS 6 microwave digestion system using a recently introduced high performance vessel to better handle the gaseous digestion byproducts. A mix of crude oil samples and NIST 1634c (Trace Metals in Fuel Oil) will be prepared and analyzed for As, V and Ni. A One Touch Method™ was created with a target temperature of 240 °C and a 20 min hold.