The impurity was obtained in the work-up by methylsulfonic acid in MeOH of the Grignard reaction in the synthesis of canagliflozin. Its structure was identified as (2S,3S,4R,5R)-1-[3-[[5-(4-fluorophenyl) thiophen-2-yl] methyl]-4-methylphenyl] hexane-1,2,3,4,5,6-hexaol (A) by HRMS and two-dimensional NMR.