Space charge reduction in TOF-MS

A method for detecting and reducing space charge effects in time-of-flight (TOF) mass spectrometry (MS) analysis, comprising:

• ionizing a compound in an ion source producing an ion beam;
• receiving the ion beam from the ion source in a mass spectrometer that includes a mass filter and a TOF mass analyzer, selecting a precursor ion mass range of the ion beam in the mass filter, mass analyzing the selected mass range in the mass analyzer, producing a precursor ion mass spectrum for the mass range, maintaining a continuous flow of selected precursor ions between the mass filter and the mass analyzer in the mass spectrometer, and applying a first set of parameters to the mass spectrometer to produce precursor ion peaks for the compound in the mass spectrum with a sensitivity above a first sensitivity threshold and a resolution above a first resolution threshold;
• detecting a space charge effect by determining if a total ion current (TIC) received from the mass spectrometer is greater than a TIC threshold or if a precursor ion peak of the mass spectrum received from the mass spectrometer has a resolution that is less than the first resolution threshold;
• and
• if a space charge effect is detected, reducing the space charge effect by having the mass filter apply to the ion beam at least one precursor ion transmission window that has a width smaller than the mass range and that is positioned to include at least one precursor ion of the compound that is multiply charged and mass analyzing in the mass analyzer, the precursor ions of the ion beam selected by the at least one precursor ion transmission window, producing a precursor ion mass spectrum for the at least one precursor ion transmission window.

A computer program product, comprising a non-transitory tangible computer-readable storage medium whose contents include a program with instructions that are executable on a processor for detecting and reducing space charge effects in time-of-flight (TOF) mass spectrometry (MS) analysis, wherein the instructions are executable on the processor to:

• provide a system, wherein the system comprises one or more distinct software modules, and wherein the distinct software modules comprise a control module and an analysis module;
• instruct an ion source device to ionize a compound of a sample using the control module, producing an ion beam;
• instruct a mass spectrometer that includes a mass filter and a TOF mass analyzer to receive the ion beam from the ion source device, instruct the mass filter to select a precursor ion mass range of the ion beam, instruct the mass analyzer to mass analyze the selected mass range, produce a precursor ion mass spectrum for the mass range, maintaining a continuous flow of selected precursor ions between the mass filter and the mass analyzer, and apply a first set of parameters to the mass spectrometer to produce precursor ion peaks for the compound in the mass spectrum with a sensitivity above a first sensitivity threshold and a resolution above a first resolution threshold using the control module;
• detect a space charge effect by determining if a total ion current (TIC) received from the mass spectrometer is greater than a TIC threshold or if a precursor ion peak of the mass spectrum received from the mass spectrometer has a resolution that is less than the first resolution threshold using the analysis module;
• and
• if a space charge effect is detected, reduce the space charge effect by instructing the mass filter to apply to the ion beam at least one precursor ion transmission window that has a width smaller than the mass range and that is positioned to include at least one precursor ion of the compound that is multiply charged and instructing the mass analyzer to mass analyze the precursor ions of the ion beam selected by the at least one precursor ion transmission window using the control module, producing a precursor ion mass spectrum for the at least one precursor ion transmission window.