1. Ion mobility spectrometry (IMS) is an important analytical technique
used to characterize gas-phase ions in an electric field at
atmospheric pressure. IMS is heavily employed in security and
military applications for explosive and drug detection, but is
increasingly being used for environmental, pharmaceutical, and
biological applications.
Most IMS designs rely on an electrically-controlled ion gate to
regulate ion flow, which can continuously allow some ions to pass
increasing baseline signal and noise. In addition, this type of ion
gate can be difficult to construct and may fail due to bent wires or
temperature fluctuations in heating and cooling cycles. This work
focuses on improving IMS by introducing and evaluating a
mechanical ion gate.
Ion Mobility Spectrometer
• Ion Source
- Spellman SL60 high-voltage power source (9,000 – 13,000 V)
- Sewing needle
• Drift Tube
- Ceramic tube with seventeen stainless steel rings separated
by ceramic spacers
- Thirty four, 1-MΩ IRC CCR9 high-voltage resistors
- Bertan Associates Inc. Series 225, (4000 –8000 V)
- Two heating rods
- Variable A/C (Staco Energy Products Co., 3PN1010)
• Detector
- Oscilloscope with Faraday cup (Tektronix TDS 340A)
• BYU-Idaho Chemistry Department
• College of Physical Sciences and Engineering
• BYU-Idaho Mechanical Engineering Department
Figure 2. Side view. Figure 3. Angle view.
Figure 4. Aluminum wheel with center hole for motor
attachment and windows for ion passage and trigger.
Figure 1. Ion mobility spectrometer.
As temperature increased drift time increased. Higher
temperatures produced more linear results with a R2 value of
0.9867 compared to 0.9333 for those of cooler temperatures.
By applying a nitrogen drift gas, average peak width decreased
by 2.5 ms. The narrowest peak width was obtained with the
drift gas at 8.5 ms with the average peak width at 16.4 ms.
Voltage is applied to the aluminum wheel by use of two wire
brushes and two 1-MΩ resistors. Temperature is applied using two
heating rods. A thermometer is inserted into the drift tube
housing to measure the approximate temperature of the drift gas.
Nitrogen gas is used as the drift gas to counter the flow of ions.
Development of a Mechanical Gate Ion Mobility Spectrometer for the
Separation of Volatile Compounds
Tyler J. Westover, Christopher Reynolds, and David C. Collins
Chemistry Department - Brigham Young University - Idaho
Introduction
Methods
Acknowledgements
Conclusion
Figure 6. Voltage vs. drift time at low (35⁰C,
blue) and high temperatures (85⁰C, red).
Results and Discussion
When employing the aluminum wheel (compared to earlier work
with a cardboard wheel), instrument stability improved and higher
voltages could be used, resulting in increased signal to noise.
As voltage applied to the aluminum wheel and drift tube
increased, ion drift time decreased.
Figure 5. Voltage vs. drift time (R2 = 0.9337).
Figure 8. Signal with drift gas.
Peak width of 16 ms.
Figure 7. Signal without drift
gas. Peak width of 17.5 ms.
Signal to noise was improved by using an aluminum wheel with
applied voltage. With the use of a trigger, ion drift times were
calculated. Increasing temperatures allowed for increased drift
times. Future work will include the manipulation of ion
window shape and the introduction of volatile species for
ionization. Also, the application of electrospray will be
investigated to introduce larger chemical species.
Mechanical Gate
• AC motor
• Variable A/C (Staco Energy
Products Co., 3PN1010)
• Aluminum wheel (23 cm o.d)
Drift Gas
• Nitrogen gas (Norco Inc.)