This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Sample matrix effects: if a sample is dissolved in a complex matrix, other compounds in the matrix can suppress the peptide signal. Clean samples give higher sensitivity than dirty samples.
Quantitation by MS: most quantitation is done by LC-UV detection at 214 nm, not by MS, because extinction coefficients are better known. MS can quantify if an internal standard is used but that requires preparation.
Worth separating two things that post #119 runs together.
Two things before anyone answers the substance.
First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.
post #123 is right about the mechanism and I think understates the practical bit.
Purity and identity are different questions: LC-MS establishes that the species at a retention time has the expected mass. It does not establish how much of the sample is that species (that is what LC-UV purity answers).
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About the Mass spectrometry category
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