A Simple Method to Determine Low Metal Concentrations in Naphtha by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES)

Inductively coupled plasma optical emission spectrometry (ICP-OES) was used in this study as an alternative analytical approach for measuring Al, Ca, Cu, Na, Ni, Si, Fe, P, V, and Zn in high-volatile petroleum products (naphtha) at the part per billion (ppb) sensitivity level. The distillation stage was intended for pre-concentrating metals by the matrix removal. Such multiplication of metal concentrations provided the possibility to measure them within the sensitivity range of the ICP-OES instrument. The reliability of such measurements was demonstrated for a wide concentration range of each metal, and the validation of the method was performed. Based on the standard deviations of nine successive measurements performed for 10 metals, the precision (repeatability) of the method for samples with concentrated metals was calculated. The values of this index (in ppb) were the following: 20.8 (Al), 20.4 (Ca), 13.7 (Na), 19.09 (Ni), 13.4 (Fe), 1.4 (P), 26.9 (V), and 45.15 (Zn). The reproducibility of the method was determined for nine measurements performed within several days. The results of recovery studies were excellent for the most part of the tested metals including Al (100.33%), Na (102%), and V (96.55%). The linearity test performed for calcium and silicon showed R = 0.999 for both elements. Depending on the standard deviation obtained in the linearity test, the limit of detection (LOD) range for all studied metals was determined to be between 2 and 10 ppb.