SelexION® Technology
Paul RS Baker
SCIEX, USA
A typical solvent for lipid analysis contains volatile salts such as ammonium acetate to improve ionization. In biological samples, Cl- ions are present, and they compete with the solvent anions to form lipid adducts, which increases the number of isobars in the sample. HPLC may not be sufficient to resolve these isobars; as a result, both may be co-isolated during precursor ion selection during MS/MS. Characterization of PC in the negative ion mode can be particularly challenging, because it exists as a mixture of anionic adducts/ions, depending on the solvent composition in which they are dissolved. Product ion analysis (MS/MS) of this mixture is key to determine composition, however mixtures of adducts can generate confounding results, which can lead to misidentification and incorrect quantification.
Differential ion mobility separation (DMS) as provided by the SelexION Technology isolates molecules based on their electrostatic properties (i.e., dipole moment), and consequently these isobars can be separated using an adduct-specific compensation voltage (CoV) during analysis via infusion or HPLC. SelexION Technology isolates the lipid adducts prior to MS/MS analysis and therefore generates spectra that are adduct-specific and clear of isobaric interference from other adducts. This enables clear identification and accurate quantification of the target lipid molecule.
SelexION Technology can isolate the different adducts of PC, which enables correct identification and accurate quantitation of individual PC molecular species.