ionsuppression

Ion suppression is a phenomenon in mass spectrometry in which the presence of co-eluting matrix components reduces the ionization efficiency of an analyte, resulting in a lower signal than would be observed with a pure standard. It is a specific form of matrix effect and is of particular concern in liquid chromatography–mass spectrometry (LC-MS) analyses that use electrospray ionization (ESI).

The suppression is caused by compounds in the sample matrix that compete for charge, alter droplet formation and evaporation in the ion source, or otherwise interfere with the generation and transmission of ions. Common contributors include salts, endogenous metabolites, phospholipids, proteins, and other co-eluting substances. Factors such as sample preparation, choice of solvent, and chromatographic conditions can influence the extent of ion suppression.

Detection and evaluation of ion suppression are typically done by comparing analyte responses in the presence and absence of matrix or by using post-column infusion or matrix factor measurements. Internal standards, especially stable-isotope-labeled analogs, are frequently employed to correct for suppression and improve quantitation. Calibration strategies include matrix-matched calibrations and standard addition to account for remaining matrix effects.

Mitigation approaches include thorough sample cleanup (for example, solid-phase extraction or protein precipitation), dilution of extracts, optimizing chromatographic separation to reduce co-elution, and switching to alternative ionization methods or instrumentation when appropriate. Awareness and correction of ion suppression are essential for accurate and precise quantitative LC-MS analyses, particularly in bioanalytical and clinical settings.