Trace Level Direct Determination of Phosphorus in Petroleum Products with High Particulate Content

Abstract

Petrochemical samples are difficult matrices, as they cover a wide range of volatilities, densities, viscosities, and quantities of particulate matter. The analysis of organic samples has always been a challenge for inductively coupled plasma – optical emission spectrometry (ICP-OES). More volatile than aqueous solutions, an organic matrix affects the plasma robustness and stability and creates complicated spectral backgrounds. As a result, the detection limits in organic as compared to aqueous samples are degraded. The goal of this study was to develop a robust and reliable method for trace level phosphorus determination in petroleum products with high particulate content. Selecting the correct sample introduction system, particularly the nebulizer as its most critical component, and optimization of instrument operating parameters are expected to significantly improve the analytical performance of the developed method. Three nebulizers were evaluated, and the analytical performance for the determination of low phosphorus concentration in a number of challenging petrochemical samples with high particulate content was compared. The evaluation included one concentric and two non-concentric nebulizers specifically designed to handle samples with large particles. In order to achieve the lowest possible quantification limits, the optimization of the dilution ratio was carried out for each studied matrix. The results clearly showed that the lowest quantification limit of 0.08 mg kg−1 at 1:3 dilution ratio as well as accuracy, precision, and ability to handle samples with high particulate content was achieved by using one of the non-concentric nebulizers.