Electronic cigarettes (ecigs) have become a popular mode of nicotine ingestion. They are often promoted as being less harmful than traditional cigarettes, but research supporting that claim is incomplete. The main chemical components of ecigs are propylene glycol and glycerol and they are usually found in a 70:30 or 50:50 ratio with 0.6 to 3.6% nicotine. Recently, Celerion Inc. was granted a patent for using isotopic propylene glycol to monitor how much PG is ingested from ecig use (vaping). The use of isotopic propylene glycol made clear delineation of ingestion of propylene glycol from foods versus ecigs. A similar method was explored for the quantitation of glycerol. Glycerol has the added challenge that lipids from the plasma – specifically triglycerides - break down into glycerol, greatly increasing the basal glycerol concentrations compared to propylene glycol concentrations. Literature values for free glycerol concentrations range from 6500-12000 ng/mL(2-4) and after breakdown of the triglycerides, total glycerides are more than 10X that. Assuming uptake similar to the propylene glycol, the Cmax for glycerol vaping would be 600-2000 ng/mL. The method detailed here deftly avoids isotopic contribution from endogenous glycerol; the result is an accurate, reproducible method for isotopic glycerol in human plasma.