Caffeine and glucosamine mobility shifts by adduction with 2-butanol depended on interaction energy, charge delocalization, and steric hindrance in ion mobility spectrometry.
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 6.9 mmol 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 (83.3 kJ/mol) than CBH+ (81.7 kJ/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.
['Meza-Morelos|Dairo|D|', 'Fernandez-Maestre|Roberto|R|http://orcid.org/0000-0001-6791-5318']
D000440:Butanols D002110:Caffeine D005740:Gases D005944:Glucosamine D000075663:Ion Mobility Spectrometry D007477:Ions D008958:Models, Molecular D009584:Nitrogen D013816:Thermodynamics
caffeine glucosamine 2-butanol ion mobility spectrometry buffer gas modifier dopant