Tungsten coil electrothermal matrix decomposition and sample vaporization to determine P and Si in biodiesel by inductively coupled plasma mass spectrometry

Abstract

A tungsten coil extracted from commercially available microscope light bulbs is used to decompose the organic matrix and vaporize biodiesel samples for P and Si determination by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). The vaporization cell is connected to a modified sheath gas tube so that sample vapors are mixed with a continuous aerosol flow exiting the ICP-MS nebulization chamber. Helium and H₂ are used with a collision–reaction interface (CRI) to minimize spectral interferences and obtain low baseline spectra. These strategies contribute to improving repeatability and accuracy. A small solid state constant current power supply is used to resistively heat the vaporizer and 10 μl sample aliquots are introduced manually on the coil with a micropipette. Limits of detection of 0.4 and 0.1 mg kg⁻¹ are obtained for P and Si, respectively. Reference biodiesel samples are used to check the accuracy of the procedure for P. A spike experiment is carried out to assess accuracy in Si determinations. No statistically significant differences are observed for reference and determined values by applying a t-test at a 95% confidence level. The direct analysis of biodiesel by tungsten coil ETV-ICP-MS is a fast and effective alternative to determine challenging elements like P and Si.