interferences, but much time can be spent changing extrac-
tion selectivity. A representative LC-MS/MS chro-
matogram for testosterone in a human serum clinical
sample is shown in the upper trace of Figure 4. Multiple
interferences prevent accurate integration of the analyte.
Note that the peak(s) at retention time 2.7 are not due to
testosterone but rather multiple interferences. If this were
the true concentration of testosterone the patient would
not be able to survive having such a high endogenous
level. The lower trace of Figure 4 shows the IS in human
serum. Multiple interferences and an elevated baseline due
to chemical background make peak integration difficult.
Figure 5 shows the same sample analyzed with FAIMS
included in the method. LC-FAIMS-MS/MS of testos-
terone in the upper trace shows that many of the interfer-
ences of Figure 4 are removed. Correct peak integration
for testosterone is now possible. The lower trace for the IS
shows that the chemical background and interferences
were eliminated. The use of FAIMS together with LC and
tandem MS has improved the selectivity of the assay,
resulting in a very accurate and precise method. The lower
level of quantitation was improved four-fold more than
the LC-MS/MS method.
Figure 4: Representative LC-MS/MS chromatogram for testosterone in a human serum clinical sample.
The upper trace is testosterone (retention time 2.7 min), the lower trace is IS (testosterone-d
3
).
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Time (min)
100000
200000
300000
400000
500000
600000
Intensity
0
500000
1000000
1500000
2000000
2500000
3000000
3500000
4000000
4500000
5000000
Intensity
2. 6
2. 7
Testosterone
without FAIMS
Testosterone-d
3
internal
standard without FAIMS
1...,48,49,50,51,52,53,54,55,56,57 59,60,61,62,63,64,65,66,67,68,...374