Figure 3.

¹H NMR spectrum for vaped pure glycerol in DMSO-d₆. These peaks labeled “L” are labile, in the context of e-liquids, hemiacetal –CH₂–OH resonances that are coupled to upfield doublets (see Figure S2), which become singlets when the –CH₂–OH is exchanged to form –CH₂–OD, as discussed in the text. The triplet in the 6.2 ppm region has already been identified as hemiacetals from PL and GL.^5,28