Correlation ion mobility spectroscopy
View Patent ↗Correlation ion mobility spectrometry (CIMS) uses gating modulation and correlation signal processing to improve IMS instrument performance. Closely spaced ion peaks can be resolved by adding discriminating codes to the gate and matched filtering for the received ion current signal, thereby improving sensitivity and resolution of an ion mobility spectrometer. CIMS can be used to improve the signal-to-noise ratio even for transient chemical samples. CIMS is especially advantageous for small geometry IMS drift tubes that can otherwise have poor resolution due to their small size.
1. A correlation ion mobility spectrometer, comprising:
a reaction region for ionizing a sample vapor to form ions,
a drift region in which the ions drift under the influence of an electric field against a counter-flowing drift gas,
means for gating a current of the ions into the drift region,
means for applying a gating function to the gating means, thereby modulating the ion current,
a detector for detecting the ions at the end of the drift region to provide an ion response signal, and
a matched filter for correlating the ion response signal with the ion current modulation to provide a correlation mobility spectrum.
2. The spectrometer of claim 1 , wherein the gating function comprises a binary modulation.
3. The spectrometer of claim 2 , wherein the binary modulation comprises a Barker code.
4. The spectrometer of claim 1 , wherein the gating function comprises an analog modulation.
5. The spectrometer of claim 4 , wherein the analog modulation comprises a chirped sinusoid.
6. The spectrometer of claim 1 , wherein the gating means comprises an ion shutter.
7. The spectrometer of claim 6 , wherein the ion shutter comprises a Bradbury-Neilson shutter.
8. The spectrometer of claim 6 , wherein the ion shutter comprises a Tyndall shutter.
9. The spectrometer of claim 1 , wherein the reaction region comprises means for pulsed photoionization of the sample vapor.
10. The spectrometer of claim 1 , wherein the reaction region comprises means for pulsed corona discharge ionization of the sample vapor.
11. The spectrometer of claim 1 , wherein the matched filter correlates the ion response signal with the gating function.
12. The spectrometer of claim 1 , wherein the matched filter correlates the ion response signal with a basis function referenced to the gating function.
13. The spectrometer of claim 12 , wherein the matched filter correlates the ion response signal, i signal (t) with a basis function, i basis (t), comprising a reactant ion response, to provide the correlation mobility spectrum, C(t drift ), according to:
C
(
t
drift
)
=
∫
-
∞
∞
i
basis
(
τ
)
i
signal
(
t
+
τ
-
t
drift
)
ⅆ
τ
≈
∑
i
=
1
n
i
basis
(
t
0
)
i
signal
(
t
0
+
t
i
-
t
drift
)
.
14. A method of correlation ion mobility spectroscopy, comprising:
providing an ion mobility spectrometer, the spectrometer comprising:
a reaction region for ionizing a sample vapor to form ions,
a drift region in which the ions drift under the influence of an electric field against a counter-flowing drift gas,
means for gating a current of the ions into the drift region, and
a detector for detecting the ions at the end of the drift region to provide an ion response signal;
modulating the gating means with a gating function, thereby modulating the ion current; and
match filtering the ion response signal with the ion current modulation to provide a correlation mobility spectrum.
15. The method of claim 14 , wherein the step of modulating comprises modulating the gating means with a binary gating function modulation.
16. The method of claim 15 , wherein the binary modulation comprises a Barker code.
17. The method of claim 14 , wherein the step of modulating comprises modulating the gating means with an analog gating function modulation.
18. The method of claim 17 , wherein the analog modulation comprises a chirped sinusoid.