LIQUID is a software program that enables users to conduct both informed and high-throughput global liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based lipidomics analysis. This desktop application can quickly identify and quantify lipids from LC-MS/MS datasets while providing a friendly graphical user interface for users to fully explore the data.

For informed data analysis, the user simply specifyies an electrospray ionization mode, lipid common name, and associated charge carrier. The software searches the loaded dataset for evidence of the specified lipid and returns the highest scored matches and associated evidence for the user to view.

For global analysis of an entire dataset, the user loads in a set of lipid targets. The software iterates over each MS/MS spectrum in the loaded dataset to find the best lipid match(es) for each.

For both informed and global analysis, the software allows the user to select a result in the output table, which triggers a graphical display of all observed and theoretical lines of evidence used for identification.

The primary evidence shown is a stem plot of the MS/MS spectra including colors and labels for peaks that match to fragments of the identified lipid. A stem plot of the isotopic profile and a line plot of the extracted ion chromatogram are also provided to show the MS-level evidence of the identified lipid. In addition to plots, other information such as intensity, mass measurement error, and elution time are also provided.

Typically, a global analysis for 15,000 lipid targets is executed in less than 5 seconds and evidence of each lipid is immediately displayed to the user.