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. Author manuscript; available in PMC: 2016 Feb 2.
Published in final edited form as: Clin Chem. 2015 Sep 14;61(11):1363–1371. doi: 10.1373/clinchem.2015.242560

Fig. 1. Structures of the substrates for assaying GALNS, ARSB, and I2S.

Fig. 1

The proton shown hydrogen bonded to the 2 carbonyl groups is the proposed site of gas phase protonation in the electrospray ion source. Internal standards lack the sulfate and contain 5 deuteriums on the benzoyl group.