Biomedical Engineering Reference
In-Depth Information
river water [
51
] and sediment [
73
], and this technique can significantly reduce the
analysis time, and increase method separation capability and detection sensitivity.
When estrogens and their derivatives of dansyl chloride and pentafluorobenzyl
bromide are analyzed by HPLC, 2D-LC and UHPLC with ESI, APCI, APPI, and
APCI/APPI MS modes, the UHPLC-ESI
−
-MS/MS signi fi cantly enhances sensitivi-
ties of the derivatives over the native estrogens, in the order UHPLC > 2D-LC > LC,
and ESI > APPI > APCI = APCI/APPI [
74
]. On the other hand, the cleaner and more
efficient supercritical fluid chromatography (SFC)-mass spectrometry was also used
for analysis of estrogens and metabolites [
75
], but the SFC technology was less
versatile and robust than LC, UHPLC, and GC.
Since the neutral molecules of steroid hormones and metabolites are not easily
ionized under either APCI
+/−
or ESI
+/−
modes, LC-MS/MS is less sensitive when
used directly in either APCI
+/−
or ESI
+/−
modes, with LOQs at ng/mL level as shown
in Table
4
[
20,
21,
52
]. It has been observed that estrone, 16a -hydroxyestrone,
2-methoxyestrone, 4-methoxyestrone, and 2-hydroxy-3-methoxyestrone are sensi-
tive to APCI
+
mode, while 2-hydroxyestrone and 4-hydroxyestrone are sensitive to
APCI
−
mode, and even more sensitive to ESI
−
mode [
29
] . Estrone, estradiol, estra-
diol, and estriol are sensitive to ESI
−
mode, and testosterone is sensitive to ESI
+
mode [
76,
77
]. Similarly, estrone and estradiol are sensitive to APPI
−
mode, and
testosterone is sensitive to APPI
+
mode with LOQs in a range of 1.5-10 pg/mL [
22
] ,
which are comparable with those steroid hormones and metabolites derivatized with
hydroxylamine or dansyl chloride, and detected under ESI
+
mode [
2,
8
] .
As most steroid hormones and metabolites are already identified, high resolution
MS technologies with higher selectivity, e.g., time of flight mass spectrometry
(TOF-MS), Fourier transform ion cyclotron resonance mass spectrometry
(FTICR-MS), Orbitrap-MS, MALDI, etc., may not have major advantages over
triple quadrupole MS in quantitative analysis, because the triple quadrupole MS
takes shorter data acquisition time, leading to a higher sensitivity. For example,
LC-ESI
−
-MS/MS is 4-6 times more sensitive than LC-ESI
−
-TOF-MS in analysis of
estrogens [
76
]. On the other hand, MS interface also plays an important role in ste-
roid hormone analysis. When analyzed by nanospray ES-Q-TOF-MS, Girard P
derivative of testosterone at 0.5 pg/mg (0.1 pg of sample) can be detected, while
10 pg of sample is needed for matrix-assisted laser desorption ionization (MALDI)-
Q-TOF-MS analysis, because of significant background interferences from the
MALDI matrix [
58
] .
GC-MS is a matured technology in analyses of steroid hormones, because
GC-MS interface and electron impact ionization (EI) MS mode are stable and easily
standardized [
1
]. GC-MS is a very powerful tool for profiling steroid hormones in
biological matrices, such as that more than 70 steroid hormones and metabolites can
be separated and quantitated by a single GC-MS run, with LOQ in range of 0.1-
10 ng/mL [
6,
48
]. The derivatization procedure may not be a challenge, because
there are many derivatization reagents available, e.g., BSTFA and MSTFA, and the
silylation reaction is straightforward and quantitative. In addition, the sensitivity of
GC-MS can be improved from low ng/mL to 0.6 pg/mL LOQ level by GC-MS/MS
technology [
23
]. That is why GC-MS is still broadly used today for analyses of
