Chasing the Bias - Gasoline Matrix Matching to Improve ASTM D2622 Sulfur Measurement Accuracy

Concerns with the quality of low-level sulfur data are on the rise amidst the implementation of US EPA Tier III, Euro 5, and Euro 6 gasoline sulfur regulations. A large part of these concerns center around bias, defined by ASTM as "the difference between the expectation of the test results and an accepted reference value". Bias can be introduced through variations in elemental composition between gasoline, diesel, and mineral oil matrices when measuring sulfur with X-ray Fluorescence (XRF) spectrometry; specifically in relation to ASTM D2622. D2622 defines several methods to handle the challenge of elemental interference, one being the matrix matching of calibration standards.

This paper explores the effects of matrix matching in two test scenarios and demonstrates how setting up a D2622 calibration curve on XOS’ Sindie 2622, a monochromatic wavelength dispersive X-ray fluorescence (MWDXRF) analyser, can help users identify the extent of and correct for sample-standard bias.