(2S,3S,4R)-1-(7,8-Dimethyl-2,4-dioxo-3,4-dihydrobenzo[g]pteridin-10(2H)-yl)-2,4,5-trihydroxypentan-3-yl dihydrogen Phosphate,(2S,3S,4R)-1-(7,8-Dimethyl-2,4-dioxo-3,4-dihydrobenzo[g]pteridin-10(2H)-yl)-2,4,5-trihydroxypentan-3-yl dihydrogen Phosphate,Riboflavin Impurity