The most common use of this data representation is when mass spectrometry is used in conjunction with some form of chromatography, such as in liquid chromatography–mass spectrometry or gas chromatography–mass spectrometry. In this case, the x-axis represents retention time, analogous to any other chromatogram.
This data representation is most commonly employed when mass spectrometry is combined with a type of chromatography, like liquid chromatography–mass spectrometry or gas chromatography–mass spectrometry. The x-axis in this context corresponds to retention time, just as it does in other chromatograms.