13C isotope fully labelled mycotoxins are internal standards for mass spectrometry. All the carbon atoms in the molecules are replaced by the stable carbon isotype. With 13C fully labelled mycotoxin standards, recovery losses from sample preparation and matrix effects in the MS source can be eliminated. BiopureTM MIX 12 contains 5 µg/mL each 13C34 fumonisin B1 and 13C34 fumonisin B2 in acetonitrile/water 50/50.