DISCUSSIONOverall, the best MS performance was obtained using the
QP instrument operated in SIM mode. Although some selectivity
was afforded by virtue of the monitoring of selected ions,
the ability to acquire complete mass spectra was precluded.
Whereas this may be satisfactory for quantitative analysis of
well-characterized samples, samples of unknown FAME composition
should be screened with full-scan MS prior to SIM
analysis for quantification. QP-SIM allowed better linearity of
response and better precision when compared with acquisition
of TIC on the same instrument and when compared with the IT
instrument. Subpicomole LOD were also obtainable in SIM
mode, a marginal improvement in the TIC LOD (typically, a
few picomoles). Even so, it should be noted that the majority
of these results occur within a rather small range regardless of
detection method, with each method being capable of a level
of performance that is acceptable for many applications