Riboflavin is an essential B vitamin for maintaining human health with key roles in energy metabolism as well as a critical component of enzyme cofactors and flavoproteins. This stable-labeled internal standard is suitable for quantification of Riboflavin in a variety of testing applications by LC/MS or GC/MS from diagnostic testing of vitamin B2 deficiency to quality control testing of vitamin B2-based dietary supplements, fortified foods or pharmaceutical preparations.