Logical Neutral Losses

Mass losses of 4 to 14 and 21 to 25 that give important peaks are highly unlikely. Remember these ranges Table A.5 presents a more complete list of them, and of neutral fragments which are commonly lost. Maximum expected relative abundances are given by Speck (1978) for example, (M — 2) is usually much less abundant than either M or (M — 1) (Section 2.6). 

If the elemental composition of the fragment lost can be deduced, this gives an even more powerful test. For example, the presence of a major (M — 15) ion is common, but a major (M — NH) ion is probably an anomalous ion the loss of 35 is logical only if chlorine is present. 

Can the ion of highest mass be the molecular ion if the following are the major ions of high mass in the spectrum  

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Triple quadrupole mass spectrometers can perform tandem mass scan experiments in various modes including product ion (MS/MS), precursor ion, and neutral loss scan and SRM experiments, but they cannot be used for sequential MS" experiments. The high sensitivity and specificity, in the SRM mode, have made triple quadrupole mass spectrometers a logical choice for metabolic stability experiments performed at relevant substrate concentrations. Despite the sensitivity of the triple quadrupole mass spectrometers, when an NCE or an NCE series exhibit unacceptable PK properties, metabolite identification studies are often initiated as follow-up studies in a separate set of experiments using incubation concentrations higher than the Km of an NCE. Incubations at higher concentrations are required because conventional metabolite identification experiments required operation of the triple quadrupole mass spectrometer in the full-scan mode, which results in poor duty cycle and diminished sensitivity [287,288],... 

Because the fragment ions corresponding to the neutral losses of 17.0, 63.0, 71.0, and 117.0amu are abiuidant and specific to carnosine adducts, it is logical to effectively perform NLS of these neutral fragments to identify the presence of 4-hydroxyalkenal species in biological samples and quantify these identified species in comparison to isotope-labeled internal standard(s) (Figure 11.3). 

It must be capable of yielding the important ions in the high-mass region of the spectrum by loss of logical neutral species (Section 3.5). 

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