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Separations of Carbohydrates with Noncovalent Shift Reagents by Frequency-Modulated Ion Mobility-Orbitrap Mass Spectrometry.

An increased focus on characterizing the structural heterogeneity of carbohydrates has been driven by their many significant roles in extant life and potential roles in chemical evolution and the origin of life. In this work, multiplexed drift tube ion mobility-Orbitrap mass spectrometry methods were developed to analyze mixtures of disaccharides modified with noncovalent shift reagents. Since traditional coupling of atmospheric pressure drift tube ion mobility cells with Orbitrap mass analyzers suffers from low duty cycles (<0.1%), a frequency modulation scheme was applied to improve the signal-to-noise ratios (SNR). Several parameters such as the resolution setting and maximum injection time of the Orbitrap analyzer and the magnitude and duration of the frequency sweep were investigated for their impact on the sensitivity gains and resolution of disaccharide-shift reagent adducts. The sweep time and disaccharide concentration had a positive correlation with SNR. The magnitude of the frequency sweep had a negative correlation with SNR. However, increasing the frequency sweep improved the resolution of mixtures of disaccharide analytes. Application of frequency-modulated ion mobility-Orbitrap mass spectrometry to four noncovalently modified glucose dimers allowed for the differentiation of three out of these four analytes.