Different approaches of crude oil mineralisation for trace metal analysis by ICPMS

Aqueous phase is the most common way to introduce samples into the ICPMS. However, due to the complexity of the crude oil matrix, harsh conditions are necessary to carry out complete acid digestion. In this work four microwave digestion methods based on maximum temperature and pressure programmes (ranging from 220 °C and 40 bar to ~ 1400 °C and 80 bar) were tested and compared with a digestion method in the High Pressure Asher (HPA-S) autoclave. Recoveries of between 80 and 120% were obtained for the different procedures evaluated. The lowest recovery and precision were obtained by the microwave-induced combustion method. The degree of decomposition of the organic material was directly related with the temperature and pressure used for the digestion. It was found that increasing the temperature and pressure by 40° and 20 bar, improved the digestion and allowed an increase in the sample size and therefore the detection limits.