External Second Gate Fourier Transform Ion Mobility Spectrometry
External Second Gate, Fourier Transform Ion Mobility Spectrometry: “FT-IMS” Next Generation Ion Mobility Spectrometer Edward E. Tarver, Ph. D. Analytical Material Sciences Department Sandia National Laboratories-Livermore, California Materials & Engineering Sciences Center Atoms to Continuum
Ion Mobility Spectrometry § Real-time response: few seconds analysis time. § Sensitivity: low part-per-billion detection without pre-concentration. § Versatility: simultaneous/universal response. § Simplicity of electronics: no vacuum pumps/chromatographs. § Field portability: low power, size and weight. Battery powered military and commercial units available. § Unattended monitoring: perimeter and network defense. Materials & Engineering Sciences Center Atoms to Continuum
63 Ni Sample Inlet Ionization Region High Voltage Repeller - Entrance Gate Ion Drift Region Focusing Rings Air Drift Gas Inlet Drift Gas Flow Drift Gas Exhaust Aperture Grid Commercial/Military IMS Drift Tube Materials & Engineering Sciences Center Atoms to Continuum Faraday Collector Signal Out
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The observed peak tailing is due to ion-molecule reactions occurring during time-of-flight and further compounded by the signal averaging process. Materials & Engineering Sciences Center Atoms to Continuum
Fourier Transform Ion Mobility Spectrometry § Increased Sensitivity, Lower Detection Limits: Sensitivity depends on the duty cycle. FT-IMS operates with 50% ion gating efficiency compared to 1% with conventional IMS. Fifty times more ions transmitted and detected than conventional IMS. § Improved Resolution, Fewer False Alarms: FT-IMS dual-gate design eliminates broadening due to ion-molecule reactions and averaging process. Conventional IMS sums all variations in ion velocity, broadening peaks and reducing resolution. No need to average with FT-IMS. § Suited for Miniaturization: FT-IMS performance allows miniaturization of detectors. § Adaptable to Current IMS Systems: No hardware modifications to drift tube. Materials & Engineering Sciences Center Atoms to Continuum
Ion Gating in FT-IMS LOW FREQUENCY HIGH FREQUENCY CYCLE REPEATED (IF DESIRED) open Entrance gate pulse closed open Exit gate pulse closed 1. Gates are open and closed for equal amounts of time no matter how frequently they are pulsed. 2. Ion collection during half of the analytical cycle time, i. e. , 50% duty cycle. 3. Low frequency greater Signal/Noise, High frequency better Resolution. Materials & Engineering Sciences Center Atoms to Continuum
Fourier Transform of the Ion Mobility Interferogram Fourier Transform Ion Mobility Interferogram Materials & Engineering Sciences Center Atoms to Continuum Ion Mobility Spectrum 8
Conventional IMS vs. FT-IMS Materials & Engineering Sciences Center Atoms to Continuum
FT-IMS Allows Tunable Resolution Materials & Engineering Sciences Center Atoms to Continuum
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TNT Response as a Function of Scanning Time Materials & Engineering Sciences Center Atoms to Continuum
PETN Response as a Function of Scanning Frequency Materials & Engineering Sciences Center Atoms to Continuum
HNS Response at 10 k. Hz and 20 k. Hz Scanning Frequency Materials & Engineering Sciences Center Atoms to Continuum
HMX Response: Frequency Range and Scan Time Materials & Engineering Sciences Center Atoms to Continuum 20
RDX Response as a Function of Frequency Range Scanned Materials & Engineering Sciences Center Atoms to Continuum
Resolution vs. Aspect Ratio as Indicator of Peak Quality RESOLUTION (R): R = Drift Time (ms) / Peak Width at Half Height (ms) • Resolution calculation ignores peak broadening below Half Height where peak tailing and overlap limits ability to separate adjacent peaks. • Drift time dependent: broad, low intensity peaks with long drift times can give higher Resolution (R) than strong, sharp peaks with short drift times. • Misleading indicator of instrumental resolving power. ASPECT RATIO: AR = Peak Height (h) / Peak Width at Base (w) • Unbiased indicator of peak quality, includes peak width below Half Height. • Aspect Ratio is Independent of drift time and describes actual peak shape. Materials & Engineering Sciences Center Atoms to Continuum
Resolution Number (Drift Time/w 1/2) 0 vs. Aspect Ratio (Peak Height/wb) R = 5/2 = 2. 5 R = 20/2 = 10 R = 32/2 = 16 AR = 3. 25/. 375 = 8. 6 AR = 8. 6 5 10 15 Materials & Engineering Sciences Center Atoms to Continuum 20 25 Drift Time (ms) 30 R = 40/2. 5 = 16 AR = 0. 235 35 40 45
Resolution in IMS Selected Bench-top IMS Instruments IMS 5000 UVIMS-MCC Itemiser Air. Sentry Ion. Scan 400 B Draeger Safety Co. Germany G. A. S. Technol. Germany G. E. /Ion Track SAES/Molecular Analytics Italy Smiths Detection Tritium 63 Ni 50 30 -60 U. S. A. or UV 63 Ni NA U. K. 63 Ni 25 44 Selected Handheld IMS Instruments RAID-M IMS Mobile µIMS Bruker Daltonics Germany Draeger Safety Co. Germany 63 Ni Tritium 30+ 50 G. A. S. G. E. /Ion Track Implant Sciences Technol. Corporation Germany U. S. A. LCD 3. 2 Smiths Detection U. K. 63 Ni Laser Corona 30 -60 NA 50 NA Materials & Engineering Sciences Center Atoms to Continuum Vapor. Tracer Quantum Sniffer Reference: Analytical Chemistry, Product Review. October 1, 2003. Pages 435 -438 A
Peak Quality Determines False Alarm Rate Peak Resolution: R = td/w 1/2 Aspect Ratio: AR = h/wb PEAK IMS Ko =1. 84 TNT PETN HNS HMX RDX Averages: SA 40. 97 41. 23 41. 94 41. 35 -----41. 37 10 K 30. 27 28. 74 28. 57 28. 84 29. 03 20 K 40 K 36. 59 39. 56 34. 31 40. 98 50. 92 37. 72 SA 10. 74 13. 68 5. 98 3. 02 -----8. 35 10 K 156. 8 209. 8 188. 4 185. 6 113. 4 170. 8 20 K 40 K 101. 6 18. 88 130. 2 36. 56 31. 89 63. 82 Ko =1. 54 TNT PETN HNS HMX RDX Averages: 45. 59 38. 20 45. 70 42. 04 46. 33 43. 57 30. 41 37. 42 26. 86 31. 76 -----31. 61 30. 75 41. 40 40. 67 41. 49 34. 11 37. 68 9. 12 5. 68 12. 8 7. 52 9. 32 8. 88 156. 8 47. 14 51. 70 147. 4 -----100. 8 134. 0 75. 90 77. 13 56. 84 17. 86 72. 34 Materials & Engineering Sciences Center Atoms to Continuum X 2 G-FT-IMS 42. 47 -----65. 99 75. 27 61. 24 IMS X 2 G-FT-IMS 56. 87 -----29. 81 ------
acetone reactant ion peak 8. 5 ms Materials & Engineering Sciences Center Atoms to Continuum RDX
8. 5 ms RDX Note the comparative resolution of the peak a 8. 5 ms. FT-IMS is able to resolve both species Present whereas signal averaging cannot. The peak at 12 ms is residual acetone. Materials & Engineering Sciences Center Atoms to Continuum
Handheld FT-IMS Materials & Engineering Sciences Center Atoms to Continuum
FT-IMS: Rear View Materials & Engineering Sciences Center Atoms to Continuum
FT-IMS: 9 -Volt Batteries in Parallel Materials & Engineering Sciences Center Atoms to Continuum
FT-IMS: Interior View Materials & Engineering Sciences Center Atoms to Continuum
FT-IMS: Vertical Battery Arrangement Materials & Engineering Sciences Center Atoms to Continuum
Acknowledgements Sandia National Laboratories, Research Foundations & Laboratory Directed Research and Development Grants Sandia National Laboratories, Livermore CA Analytical Material Sciences Department Dr. Jim Wang, Mr. Anh Phan, Dr. Kent Pfeiffer, Mr. John Warmouth Professor Herbert Hill, Washington State University, Pullman WA Professor David Harris, Harvey Mudd College, Claremont CA United States Department of the Navy: Contract N 4175603 GO 14803 Materials & Engineering Sciences Center Atoms to Continuum
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