Biomedical Engineering Reference
In-Depth Information
However, most modern highly accurate time-of-flight (TOF), Fourier-transform
ion cyclotron resonance (FT-ICR) and Orbitrap mass analysers [
107
] have not been
reported for TA analysis so far and are thus not discussed in this chapter.
Depending on the instrumental set up and study purpose different scan modes
were selected, which are addressed below (Fig.
5b
).
3.3.3
Scan Modes
The scan mode determines the extent and quality of mass spectrometric data and has
thus to be chosen with respect to the analytical requirements. Detection of unknown
compounds, identification of unknown structures and confirmation of known mol-
ecules as well as quantification of distinct target analytes require different scan
modes for reliable optimum analytical acuity.
3.3.3.1
Full Scan (MS)
The most simple, least sensitive and less selective scan mode is the ordinary MS full
scan covering a pre-adjusted
m
/
z
range. This procedure is well suited for the simul-
taneous detection of known and unknown intact compounds that may have been
produced by, e.g. chemical synthesis or biotransformation processes in vitro and
in vivo. For retroactive data processing
m
/
z
ratios of interest are extracted to gener-
ate extracted ion chromatograms that illustrate only the selected mass traces and
thus depict the analytes' chromatographic behaviour. No need for predefinition of
analyte masses represents a major advantage of this scan option thus avoiding to
overlook compounds of interest.
A quite early LC-ESI MS approach was presented by He et al. in 1995 using a
SQ analyser for the detection of benztropine and its biotransformation products in
urine and bile after oral administration of the drug to rat [
59
] (Table
7
). However,
the lack of additional structure elucidation by mass spectrometric fragmentation
restricted the analytical significance of the SQ instrument.
A similar full scan MS approach was presented by Tang et al. for screening of
quarternary ammonium compounds and quantification of ipratropium in horse urine
[
24
] (Table
5
). However, they used an IT mass spectrometer that additionally allowed
confirmatory analysis of the drug by MS/MS experiments for verification of HPLC
peak-drug assignment.
3.3.3.2
Selected Ion Monitoring
In contrast to the full scan MS mode discussed above, SIM provides improved sen-
sitivity but requires preselection of analyte ions thus preventing from posterior
search for unknown substances.
