Biomedical Engineering Reference
In-Depth Information
a
b
c
Ionization methods
Scan modes
Mass analysers
+APCI
14%
SQ
21%
MS/MS
18%
FAB
4%
+TSP
2%
MS
4%
MRM
61%
Q
q
Q
56%
+ESI
80%
IT
19%
SIM
17%
EBQ
1
Q
2
4%
Fig. 5
Statistical evaluation of LC-MS-based methods for tropane alkaloids referred in this chap-
ter. (
a
) Relative frequency of ionization methods.
+APCI
positive atmospheric pressure chemical
ionization,
+ESI
positive electrospray ionization,
FA B
fast atom bombardment,
+TSP
positive
thermospray. (
b
) Relative frequency of scan modes used.
MS
full scan MS,
MS/MS
tandem mass
spectrometry (product ion scan),
MRM
multiple reaction monitoring,
SIM
selected ion monitoring.
(
c
) Relative frequency of mass analysers used.
EBQ
1
Q
2
double focusing sector field mass spec-
trometer,
IT
ion trap,
QqQ
triple quadrupole,
SQ
single quadrupole. Considered publications were
found by PubMed data-based search and references cited in these articles
With respect to matrix effects Björnstad et al. observed maximum reduction in
MS detector signals at the void time of chromatographic separation when
analysing urine containing atropine and scopolamine relinquishing any sample
preparation step [
55
]. This was due to salts, amino acids and many other highly
polar urine components that were not retained on RP material. However, such
effects could be compensated by using deuterated IS being ionized under identi-
cal conditions as the analytes and were obsolete for atropine and scopolamine
that showed remarkable retention.
Suppressing matrix effects on ionization of ipratropium (21 % suppression) were
described by Ariffin and Anderson when analysing SPE extracts of whole blood by gradi-
ent RP-LC-ESI MS/MS [
54
]. In contrast, only slight ion suppression was described by
John et al. for simultaneous measuring of cocaine (4 %), homatropine (4 %), ipratropium
(4 %),
S
-hyoscyamine (3 %), littorine (1 %),
N
-butyl-scopolamine (1 %), and scopol-
amine (10 %) by gradient RP-LC-ESI MS/MS [
50
]. In this study plasma samples were
precipitated with acetonitrile and the supernatant was further diluted prior to injection.
Besides TTA and QTA analysis, high popularity and wide spread applicability of
ESI is also found for numerous additional substances, e.g. peptides [
103
] and
organophosphorus compounds [
104
] .
3.3.2
Mass Analysers
Whereas the interface produces analyte ions the mass analyser identifies the cor-
responding masses or may allow fragmentation for tandem-mass spectrometry
(MS/MS or MS
2
) or multiple fragmentation (MS
n
). Single quadrupole (SQ), triple
