Drift Time or Collision Cross Section in Ion-Mobility Separation

4 Drift Time (or Collision Cross Section) in Ion-Mobility Separation 

Ion-mobility mass spectrometry (IM-MS) has emerged as an important analytical method in the last decade [74]. In IM-MS, ions are generated by pyrolysis, electrospray, laser desorption, or other ionization techniques prior to their entry into a gas-filled mobility drift cell. In this cell, ions drift at a velocity obtained from an electric field based on their shapes or dipoles in the case of differential mobility spectrometry (DMS). The greater the cross section of an analyte is (i.e., the larger the ion 

IM-MS is particularly useful for analysis of isobaric and isomeric lipid species, which possess different structures or configurations. For example, MALDI-IM MS has been used to analyze gangliosides, a class of complex glycosphingolipids 

Collectively, IM-MS clearly provides separation of lipid classes according to their charge properties, individual molecular species of a lipid class based on their molecular size (including chain length and unsaturation), and isobaric/isomeric species possessing different conformational structures [83]. This in situ drift time/collision cross section variation could be used as an additional variable to the other separation variables (e.g., intrasource separation, LC-MS elution, and optimal selection of MALDI matrix for ionization) described earlier as an aid to providing 3D analysis of complex lipid mixtures. 

(a) Bligh, E.G. and Dyer, W.J. (1959) A rapid method of total Upid extraction and pnrifi-cation. Can. J. Biochem. Physiol. 37,911-917. 

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