Ion suppression

Ion suppression is a reduction in the mass spectrometry response of an analyte caused by other sample constituents affecting ion production or the ion source response. The same amount of analyte can consequently yield a smaller signal in a complex sample than in a reference solution. It is one direction of a mass spectrometry matrix effect; enhanced response is also possible. A weak peak therefore need not mean that less analyte was originally present.

A 2003 experimental study separated matrix-response effects from analyte recovery in quantitative liquid chromatography–mass spectrometry. For its investigated compound, changing from ion spray to a heated-nebulizer interface removed a matrix effect under otherwise matched sample preparation and chromatographic conditions. This is evidence that the source interface matters, rather than a guarantee that one interface avoids suppression for every compound.^[ref]

An original matched-spike example distinguishes two losses. Give equal final analyte amounts to a neat reference and to an extracted blank sample after preparation. Suppose their peak areas are $1000$ and $400$: the relative matrix response is $400/1000=0.40$, corresponding to $60\%$ suppression relative to the reference. Now spike the same nominal amount before preparation; an area of $240$ gives an estimated recovery of $240/400=0.60$ and overall process response $240/1000=0.24$. This interpretation assumes matched final volumes, injections and response conditions. It separates material lost during preparation from reduced response of material that remains.

Detector signal clipping is a different mechanism: a recording ceiling can lose intensity after ions have been produced. Neither that loss nor analyte-specific ion suppression is generally repaired by total ion current normalization. Distinguishing the mechanisms requires controls at the stages where the signal can change.