1. Introduction
Experimental
Ion Mobility Spectrometer (Figure 1)
• Drift Tube
- Ceramic tube with 17 stainless steel rings separated
by ceramic spacers
- Thirty two, 1-MΩ IRC CCR9 high-voltage resistors
- Power supply (Bertan Associates Inc. Series 225, 8.2 kV)
• Detector
- Oscilloscope (Tektronix TDS 340A) with copper Faraday cup
• Mechanical Gate (Figure 2)
- AC motor
- Variable A/C (Staco Energy)
- Aluminum wheel (23 cm o.d.)
• Aperture Grid (Figure 3)
- Stainless steel rings and wires
- Coarse and fine patterns
Results
Conclusion
Acknowledgements
• BYU-Idaho Chemistry Department
• College of Physical Sciences and Engineering
Results Continued
Figure 1. Ion mobility spectrometer.
Paper spray (PS) ionization is a new ionization technique used to
create ions at atmospheric pressure for analysis, without the use
of a mechanical pump. Ions are created by applying a high
voltage to a paper triangle wetted with an analyte solution (< 10
µL). Because PS is used more regularly with mass spectrometry,
its use with ion mobility spectrometry (IMS) is minimal; and,
there are no reports of PS with mechanical-gate IMS. This work
focuses on pairing PS with a mechanical-gate IMS to detect and
separate herbicide ions in an attempt to further develop our
novel IMS instrument. Also, the use of aperture grids in front of
the detector was investigated to reduce signal width.
Aperture Grid
• Three aperture grids were investigated to decrease signal
width. All grids significantly lowered signal (Figures 8-10).
Paper Spray Ionization (Figures 4 and 5)
• Source
- Spellman SL60 high-voltage power supply (9 – 11 kV)
- Whatman #1 filter paper cut into triangles
• Samples
- Blank: 70:30 methanol/water, 1 % (w/w) acetic acid
- Herbicide solution: same as blank plus 100 µM prometon
Initial Results
• Dry paper did not produce signal (Figure 6). Un-gated signal
was obtained after saturating the paper with sample (blank
or herbicide) solution (Figure 7 ).
Paper spray ionization was successfully interfaced with ion
mobility spectrometry. Aperture grids decreased peak width at
the cost of signal. PS-IMS signal was obtained for blank and
herbicide samples. Blank signal consistently resulted in two
peaks and was likely due to protonated ion clusters of water
and methanol. Prometon herbicide signal consistently resulted
in three peaks. The third peak was likely due to protonated
prometon clusters with water and methanol. Future work will
include peak width reduction (employing a counter flow of
heated nitrogen gas) and peak identification.
Detection of Herbicide Ions Using Paper Spray Ionization
with a Mechanical Gate Ion Mobility Spectrometer
Tyler J. Westover, Kyler W. Pugh, and David C. Collins
Chemistry Department - Brigham Young University - Idaho
Figure 8. Signal
from coarse
aperture grid.
Figure 5. Source.Figure 4. Illustration of paper spray.
Figure 2. Gate.
Experimental Continued
Figure 3. Aperture grids investigated.
Figure 9. Signal
from fine aperture
grid.
Figure 10. Signal
from (parallel wires)
aperture grid.
Blank Solution
• All results were obtained without an aperture grid.
• Signal was greatly increased
• Two peaks were consistently identified (Figure 11a-c).
Figure 6. Signal of dry
paper.
Figure 7. Signal of
blank-saturated paper.
Figure 11. Blank samples without aperture grid.
a) b) c)
1
2 1 2 1
2
Herbicide Solution
• All results were obtained without an aperture grid.
• Three peaks were consistently recognized (Figure 12).
• Prometon is a basic compound easily ionized by acetic acid
(Figure 13).
Figure 12. Prometon
herbicide sample.
1
2
3
Figure 13. Chemical structure
of prometon.