Elemental Analysis of Crude Oils Using Microwave Plasma Atomic Emission Spectroscopy

Trace elemental analysis using microwave-induced plasma (MP) generated by nitrogen gas was employed as an atomization and excitation source for emission spectrometric (microwave plasma atomic emission spectroscopy, MP-AES) analysis for crude oil samples. Nitrogen gas produced from air through a gas generator, and in combination with an external gas control module (EGCM) used to introduce air into the plasma, leads to a stable robust microwave-induced plasma, enough to perform the analysis of crude oil samples with different API values, sulfur (0.5-5 wt %) and nitrogen (500-2500 mg/kg) by direct dilution in a o-xylene diluent. Excellent detection limits and spike recoveries at low and high concentration levels were determined for Ni, V, Fe, Ca, and Na in crude oil matrix. The recoveries obtained from the analysis of the three quality control (QC) test materials were within +/- 10% of the actual/certified values. Comparable results for Ni and V as well as the V/(V + Ni) ratio in crude oils between nitrogen plasma and conventional argon plasma such as inductively coupled plasma atomic emission spectroscopy (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) were achieved in terms of precision, relative standard deviation, and recoveries for the concentration range from 2 to 230 mg/kg.