Dynamic Quadrupole Selection to Associate Precursor Masses with MS/MS Products in Data-Independent Acquisition

Data-independent acquisition (DIA) mass spectrometry facilitates high-throughput, reproducible bottom-up proteomic analyses. Typically, DIA methods coselect multiple precursor ions within a wide selection window. These precursors are simultaneously fragmented, superimposing the product ion signals into a complex chimeric spectrum. A method for varying the quadrupole selection width over the ion accumulation period is described. This method couples the intensity of a product ion to the mass of its precursor ion. By overlapping consecutive selection windows, scan-to-scan product ion intensity profiles can be used to infer precursor mass. We assess the method's sensitivity to quadrupole width, accumulation time, and mass-to-charge range using internal fluoranthene calibrant and FlexMix calibration solution with Q-Orbitrap configured mass analyzers. Additionally, we explore usability of the described technique on a tryptic-digest monoclonal antibody sample, including both direct infusion and liquid chromatography of the sample. With direct infusion, product ions from two precursors separated by 1 thomson (Th) are resolved with this method using 10 Th windows with 5 Th overlap. The product ions are associated within 0.3 Th of their respective precursor ion's <i>m</i>/<i>z</i>. Therefore, product ion spectra have a precursor ion <i>m</i>/<i>z</i> resolving power of ∼33.