Determining sulfur by inductively coupled plasma mass spectrometry (ICP-MS) is not a trivial task especially due to the intense spectral interferences caused by polyatomic ions such as 16O2+, (16OH)2+, 14N16OH2+ and 14N18O+. In this work, argon species naturally present in the plasma (interference standards, IFS) are used to minimize spectral interferences on sulfur determination in biodiesel microemulsions. An external calibration method using ratios between analytical and IFS signals is employed in all determinations. The limits of detection (LOD) calculated for the 32/36, 34/36, 34/37 and 34/38 signal ratios were 4.0, 1.0, 1.0 and 0.8 mg L-1, respectively. A standard reference material (Lubricating Oil, SRM 1848) and spiking studies in biodiesel samples were employed to check the method accuracy. Recoveries varied from 77 to 105% while using any of the IFS probes (36Ar+, 36ArH+ or 38Ar+).
IFS species; spectral interferences; mass spectrometry; biodiesel; microemulsions
