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I am currently studying the textbook Mass Spectrometry - A Textbook, third edition, by Jürgen Gross. Chapter 1.4.4 Mass Spectrum says the following:

The most intense peak of a mass spectrum is called base peak. In most representations of mass spectral data the intensity of the base peak is normalized to 100% relative intensity. This largely helps to make mass spectra more easily comparable. The normalization can be done because the relative intensities are basically independent from the absolute ion abundances registered by the detector.

I don't understand how it makes sense to say that the relative intensities are independent from the absolute ion abundances. It seems clear to me that the contrary is true; that is, that the relative intensities are derived from the recorded absolute ion abundances registered by the detector, and so the relative intensities are dependent on the absolute ion abundances. After all, the detector records the absolute ion abundances first, and then uses these values to calculate the relatives intensities, right? I'm not sure that it would make much sense to say that it was the other way around.

I would greatly appreciate it if people would please take the time to clarify this.

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    $\begingroup$ I think this is simply sloppily written/translated. The pattern (positions & intensities) for a single substance is always the same if you use the same ionisation technique (esp. same voltage) and measure long enough. The absolute intensity is only very loosely correlated with the abundance of the compound in your sample. Ionisation efficiency varies all over the place. $\endgroup$ – Karl Jun 11 at 10:54
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    $\begingroup$ Some detectors may saturate at high count rates, or you get pulse pileup issues, or whatnot, but if you are below the total count rate that causes that, you should be recording the same spectrum regardless of count rate. $\endgroup$ – Jon Custer Jun 11 at 13:36
  • $\begingroup$ @JonCuster Oh, I think I understand what the author is trying to say. He doesn't mean that the absolute abundances are not used in deriving the relative intensities; what he means is that, regardless of the varying levels of absolute abundances, the relative intensities pattern will always be the same for the same sample. Is this correct? $\endgroup$ – The Pointer Jun 11 at 19:04
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    $\begingroup$ That´s what I meant by "measure long enough". You count fragments reaching the detector. The pattern develops purely statistical. $\endgroup$ – Karl Jun 11 at 19:46
  • $\begingroup$ @Karl Ok, thanks for the clarification. $\endgroup$ – The Pointer Jun 11 at 19:53

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