The effect of adduction energy and intramolecular bonding in the mobility of dextromethorphan and diphenhydramine with 2-butanol in the buffer gas in ion mobility spectrometry

Publication date: Available online 18 September 2017 Source:Microchemical Journal Author(s): Dairo Meza-Morelos, Roberto Fernandez-Maestre Ion mobility spectrometry (IMS) separates gas-phase ions moving under an electric field according to their size to charge ratio. We used electrospray ionization IMS-mass spectrometry and computational chemistry to study the mobility shifts of the drugs dextromethorphan (Dx) and diphenhydramine (Dy) with the introduction of 2-butanol (B) as a shift reagent (SR) caused by non-covalent adduction of Dx and Dy with B. The binding energies of 2-butanol-ion adducts were calculated using Gaussian 09 at two different levels of theory: M06-2X/6-311++(d,p), used to discuss the present results, and B3LYP-GD3/6-311++(d,p). We found the reduced mobility (K0) of Dx to decrease by 1.4% and that of Dy by 0.4% when the concentration of 2-butanol changed from 0.14 to 1.4mmolm−3 in the buffer gas. This was unexpected from the molecular weights of these compounds, Dx 272.4g/mol and Dy 256.4g/mol (small ions suffer large mobility shifts), nor from the apparent steric hindrance on the positive nitrogen in Dx for the adduction of 2-butanol molecules. This hindrance should have produced a smaller mobility shift for Dx than for Dy due to a reduction in clustering with 2-butanol. However, these shifts could be explained on the interaction energies of these ions with 2-butanol. The formation of DxBH+ was favored over that of DyBH+ due to the formation of more s...

Source: Microchemical Journal - September 19, 2017 Category: Chemistry Source Type: research