Solvent Yellow 124 (SY124, N-ethyl-N-[2(isobutoxyethoxy)ethyl]-4-(phenylazo)aniline) is used as a common low tax fuel marker in European Union member countries. It is added to these fuels which may also contain traditional dyes, to prevent misuse. SY124 is produced industrially in solution (typically aromatic hydrocarbons) and its purity can vary from batch to batch. This is particularly a problem for the petroleum industry which risks large fines if SY124 levels are found to be below 6 mg/L or above 9 mg/L. A new reference material for SY124, certified for purity was prepared to address this problem. A SY124 CRM was prepared from a commercially procured solution of SY124. The details of the preparation and certification will be discussed. The material is commercially available as ERM-AC316a, packaged as 200 mg units in screw cap 4 mL. amber glass vials. Its purity value is 95.0 +/- 1.2% m/m at the 95% confidence interval. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.