Enhanced direct analysis of organic samples using a high temperature total consumption sample introduction system coupled to microwave plasma optical emission spectrometry (MIP-OES)

Abstract

This work presents the coupling of a high temperature Torch Integrated Sample Introduction System (hTISIS) to microwave plasma optical emission spectrometry (MIP-OES) for multielemental analysis of organic samples, specifically biofuels and oils. An innovative method for automated, routine analysis of organic samples by MIP-OES, using continuous sample delivery to the spectrometer has been developed. The hTISIS, operated at 300 °C, significantly improved analyte transport efficiency and mitigated matrix effects. Limits of quantification (LOQs) achieved at a 40 μL min^-1 liquid flow rate were markedly reduced compared to conventional sample introduction system at 250 μL min^-1. Values ranged from 2 μg kg^-1 for Cu to 100 μg kg^-1 for Pb and 200 μg kg^-1 for Zn, compared to 70 μg kg ^-1, 700 μg kg^-1 and 30 μg kg^-1 obtained with the conventional device, respectively. Recovery tests across six oil and fat samples validated the method accuracy, with recovery rates between 90 and 110 % achieved without the use of an internal standard, demonstrating effective matrix effect mitigation at 300 °C. Under these conditions, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Pb, Si and Zn concentrations were determined in six oil and fat samples. The analysis of samples was done after dilution (1:20) using xylene as the diluent to ensure proper sample introduction. The concentration values were compared with those found by applying the reference method UOP 389-15 and statistically equivalent values were found, establishing the robustness and precision of the hTISIS-MIP-OES for direct elemental profiling of organic matrices.

Keywords: Biofuel raw materials; Grease analysis; MIP-OES; Oil analysis; hTISIS.