Caffeine and glucosamine mobility shifts by adduction with 2-butanol depended on interaction energy, charge delocalization, and steric hindrance in ion mobility spectrometry

摘要

Ion mobility spectrometry (IMS) is an analytical technique that separates gas-phase ions drifting under an electric field according to their size to charge ratio. We used electrospray ionization-drift tube IMS coupled to quadrupole mass spectrometry to measure the mobilities of glucosamine (GH(+)) and caffeine (CH+) ions in pure nitrogen or when the shift reagent (SR) 2-butanol was introduced in the drift gas at 6.9mmol m(-3). Binding energies of 2-butanol-ion adducts were calculated using Gaussian 09 at the CAMB3LYP/6-311++G(d,p) level of theory. The mobility shifts with the introduction of 2-butanol in the drift gas were -2.4% (GH(+)) and -1.7% (CH+) and were due to clustering of GH(+) and CH+ with 2-butanol. The formation of GBH(+) was favored over that of CBH+ because GBH(+) formed more stable hydrogen bonds (83.3kJ/mol) than CBH+ (81.7kJ/mol) for the reason that the positive charge on CH+ is less sterically available than on GH(+) and the charge is stabilized by resonance in CH+. These results are a confirmation of the arguments used to explain the drift behavior of these ions when ethyl lactate SR was used (Bull Kor Chem Soc 2014, 1023-1028). This study is a step forward to predict IMS separations of overlapping peaks in IMS spectra, simplifying a procedure that is trial and error by now.