A novel double disc electrode excitation method for oil elemental analysis in rotating disc electrode-optical emission spectrometry (RDE-OES)†

Abstract

Rotating disc electrode-optical emission spectrometry (RDE-OES) is a leading technology for detecting oil elements. However, electrode wear impedes sample combustion and spectral stability, causing errors in acquisition and analysis. In this work, we propose and develop a novel arc excitation method with a double disc electrode structure, replacing the conventional upper rod electrode with a disc electrode of the same type as the lower electrode, and the double electrodes rotate simultaneously. This method minimizes wear and maintains a constant gap, enabling a long-lasting, energy-focused arc and high-intensity, stable spectrum. Our method is validated by analyzing the spectral lines of Al, Mg, Cr and Ca. Compared with the conventional method, the results revealed that our method can improve calibration robustness, with a 2–3 times higher spectral intensity and 1–3 times higher signal-to-noise ratio (SNR) with an 8–10% reduction in the relative standard deviation (RSD) values. R² for Al, Ca, Cr and Mg increased from 0.9872, 0.9772, 0.9824, and 0.9832 to 0.9988, 0.9994, 0.9998 and 0.9997, respectively, and the limits of detection (LODs) decreased from 2.0, 1.8, 1.7, and 1.9 ppm to 1.9, 1.6, 1.6 and 1.7 ppm. Our method achieved consistently high and stable spectral intensity and significantly reduced electrode wear during excitation, with the outer diameter change being 44.4% of the rod electrode length change after 50 excitations. The results demonstrate the method's ability for signal stability and accurate quantitative analysis, highlighting RDE-OES's importance in oil analysis.