13C6 Glucosylsphingosine (d18:1) is an isotopically enriched form of 1-β-D-glucosylsphingosine (d18:1) that is intended for use as an internal standard for the quantification of 1-β-D-glucosylsphingosine by GC- or LC-MS. 1-β-D-Glucosylsphingosine is a lysolipid derivative of glucosylcerebroside that decreases activity of glucocerebrosidase in LA-N-2 cells in a dose-dependent manner.