Determination of Trace Sulfur in Biodiesel and Diesel Standard Reference Materials by Isotope Dilution Sector Field Inductively Coupled Plasma Mass Spectrometry
Steven J. Christopher, Stephen E. Long, Renata Amais, Joaquim N¿ga
A method is described for quantification of sulfur at low concentrations on the order of 10 µg g-1 in biodiesel and diesel fuels using double isotope dilution and sector field inductively coupled plasma mass spectrometry (ID-SF-ICP-MS). Closed vessel microwave digestion was employed using a diluted nitric acid and hydrogen peroxide decomposition medium to reduce sample dilution volumes. Medium resolution conditions were employed to eliminate isobaric interferences at 32S and 34S related to polyatomic phosphorus and oxygen species. The method outlined yielded respective limits of detection (LOD) and limits of quantification (LOQ) of 0.7 µg g-1 S and 2.5 µg g-1 S (in the sample) and was employed to value assign total S mass fraction in NIST SRM 2723b Sulfur in Diesel Fuel Oil at 9.06 µg g-1 ± 0.13 µg g-1. No statistically significant difference at a 95 % confidence level was observed between the measured and certified values for control samples.