Submitted to: AOCS Lipid Library
Publication Type: Trade Journal
Publication Acceptance Date: 9/1/2012
Publication Date: 9/1/2012
Citation: Byrdwell, W.C. 2012. Parallel mass spectrometry (APCI-MS and ESI-MS) for lipid analysis. AOCS Lipid Library. www.lipidlibrary.com.
Interpretive Summary: Mass spectrometry is a method for converting molecules into ions and then analyzing the masses of those ions to determine what the structures of the molecules are. There are several different possible ways to produce the ions, and the structural information that comes from the molecules depends on how they were ionized. Different types of ionization produce different types of ions from the molecules, and some types of ionization produce more fragments from the molecules than others. It is beneficial to obtain data from different types of ionization, since the structural information deduced from each type of ionization is complementary to the other. We have shown that obtaining multiple types of data from multiple mass spectrometers, simultaneously in parallel, allows more information to be determined with greater confidence than the data from any single instrument alone. This article describes our pioneering work to use multiple mass spectrometers in parallel for lipid and vitamin D analysis.
Technical Abstract: Coupling the condensed phase of HPLC with the high vacuum necessary for ion analysis in a mass spectrometer requires quickly evaporating large amounts of liquid mobile phase to release analyte molecules into the gas phase, along with ionization of those molecules, so they can be detected by the mass filtering device. The processes of nebulization and ionization usually occur at atmospheric pressure, and thus the formation of ions under these conditions is called “atmospheric pressure ionization” (API). The three most commonly used API techniques are atmospheric pressure chemical ionization (APCI), electrospray ionization (ESI), and atmospheric pressure photoionization (APPI). All three of these common API sources provide ‘soft’ ionization of molecules, usually with a protonated molecule or molecular adduct ion, and a few large fragments. However, the relative proportions of the intact protonated molecule and adduct ions versus the fragments distinguishes ESI from APCI, and is the reason that the data from these techniques is complementary and both are valuable and desirable. Acquisition of ESI-MS and APCI-MS data can be accomplished using a single mass spectrometer, by performing one type of analysis and then changing ionization sources and re-analyzing the same sample. But this is time-consuming and requires twice as many resources (solvents, gases, time, etc.) as a single run. An obvious alternative is to acquire both types of data simultaneously, using a multiple parallel mass spectrometry approach. This article describes the benefits of acquiring different types of mass spectrometry data simultaneously in parallel for analysis of vitamin D and triacylglycerols.