A mock mixture of three isomeric glycerophosphatidylcholines was analyzed via LC-Oz-IM-MS. (A) With the device turned off, the EIC trace of m/z 786.6 shows separation into cis and trans isomers, and no diagnostic ozonolysis fragments are detected. (B) Activation of the ozonolysis device reveals the presence of two distinct cis double bond positional isomers at the 6Z and 9Z positions, with diagnostic aldehyde fragments at m/z 634.4 and 676.6, respectively, underneath the second LC peak in the EIC trace.