10/8/ nd Gen Results at ~0.7 Torr Ar or O 2 rf= 75 MHz, 5 Hz modulation frequency (0-120 mv pp ) through 50 db linear amplifier & transformer.

Transcription

1 2 nd Gen Results at ~0.7 Torr Ar or O 2 rf= 75 MHz, 5 Hz modulation frequency (0-120 mv pp ) through 50 db linear amplifier & transformer. Development of a Loeb-Eiber Mass Filter for Portable Mass Spectrometry (for Harsh Environments) Glen Jackson, Feng Jin, William D. Hoffmann Forensic & Investigative Science & C. Eugene Bennett Department of Chemistry West Virginia University, Morgantown, WV Oglebay Hall Morgantown, WV glen.jackson@mail.wvu.edu

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3 Bracken Bat Cave posed airborne microbes, flesh-eating insects and toxic levels of ammonia and urea from millions of Mexican Freetail Bats Environmental Monitoring htttp:ptrms.com (Ionicon) T. Short et al., U. South Florida 12 3

4 Environmental Monitoring Environmental Monitoring G. M. McMurty et al., U. Hawaii Portable Mass Spectrometers Z. Ouyang, R. G. Cooks et al., Purdue U

5 Why MS? MS advantages (bench top) High specificity Low detection levels Broad screening ability Identified as core technology for explosive and biochemical detection by TSA study 17 Committee on Assessment of Security Technologies for Transportation, 'Opportunities to Improve Airport Passenger Screening with Mass Spectrometry', National Research Council, Washington, (2004). 18 Advantages/Disadvantages of Miniaturizing Mass Spectrometers Gravity Versus Human Engineering Disadvantages Higher (worse) limits of detection Lower (worse) resolving power Advantages Solve the problem (on-site, real-time detection) More robust If scale is reduced by factor x, mass reduces by x 3 F=mA Less impact when dropped!

6 1948 Westinghouse Electric s Portable Mass Spectrometer 1957, Bennett Mass Spectrometer Orbits Earth in Sputnik I Measuring Mass; Grayson M.A., Ed.; Chemical Heritage Press; Philadelphia, PA, Process Monitoring Why can t we make mass spectrometers smaller?

7 Mass Filters Can be Small The mass filter isn t the problem is typically ~1% volume of the instrument G. Verbeck, U. North Texas 25 Kornienko O. et al., Rapid Commun. Mass Spectrom. 1999, 13, Austin, D.E., Cruz, D., Blain, M.G., J. Am. Soc. Mass Spectrom. 2006, 17, Enablers are the Problem What s the solution?

8 Need small dimensions and/or fast filtering Small/fast filters overcome issue of mean free path Higher operating pressure Small dimensions allow small voltages to obtain necessary field strength, E (E=V/d) Lower voltage requirements e.g V cm = 1000 V 10 mm or 1 V 10 m Less power consumption Loeb-Eiber Mass Filter 1921 Loeb reported use of interleaved wires to filter electrons 1930s Loeb, Cravath, Van de Graaff, Bradbury & Nielsen and others use filters for blocking electrons, too 1963 Eiber changes operating conditions to filter ions 200 m wires, 2 mm spacing 1-9 MHz, 500 V Smaller batteries 29 L.B. Loeb, Phys. Rev., 1935, 17, Eiber s Mass Filter Loeb-Eiber Filter versus Bradbury-Nielsen Gates? Loeb-Eiber filter Loeb (Bradbury-Nielsen) gate Has low mass cut off All or nothing Eiber, V. H. The Measurement of Ion Masses at Pressures up to Several Torr with a Grid Filter Z. Angew. Physik 1963, 15, Eiber, V. H. The Measurement of Ion Masses at Pressures up to Several Torr with a Grid Filter Z. Angew. Physik 1963, 15,

9 Round or Square Wires? Linear vs Quadratic Fields Equipotential field lines for A) Loeb-Eiber MF and B) Quadrupole MF Ions in Linear Fields Ions in Linear Fields When phase = 0, t=0 Sinusoidal motion + y-offset When phase 0 Sinusoidal motion - linear motion + y-offset

10 Solutions for y at Different Phases Simulations: Phase Angle freq = 68 MHz, RF voltage = 10 V PP, D= 75 um, d = 25 um, m/z = 40 TOB = 0 rad, π rad, π/2 rad Starting Time and Position of Ions? freq = 80 MHz, RF voltage = 10 V PP, D= 75 um, d = 25 um TOB = 0 usec (phase ~ constant) blue = m/z 40, red = m/z 80 Ions in Linear Fields y max = maximum time independent amplitude of oscillation Same solution given by Eiber in 1963 If 2(y max ) inter-wire distance (d), all ions of select m/z will strike an electrode If 2(y max ) < inter-wire distance (d), some proportion of ions of select m/z will strike an electrode

11 Ideal Ion Signal (Transmitted Ions) mass m1 > mass m2 # ions m1 = # ions m2 Traveling wave IMS-MS at 1.7 Torr Eiber s Original Data Itotal Total Ion Current Im1 y max (m2) = d Im2 y max (m1) = d RF Amplitude (V0 P) 41 Eiber, V. H. The Measurement of Ion Masses at Pressures up to Several Torr with a Grid Filter Z. Angew. Physik 1963, 15, st Generation Filter 1 st Generation Filter Spooling the Nitinol Wires onto the Polyimide Loeb-Eiber Support Precision Microfab, Inc st generation: winding first wire in Loeb-Eiber Filter 44 11

12 1 st Generation Filter 1 st Generation Filter Transmitted Light Microscopy Final Loeb-Eiber Filter Array of Alternating Isolated Wires st Generation Filter Transmitted Light Microscopy Problems with Electrical Short D = 75 m

13 2 nd Generation Loeb-Eiber Filter 2 nd Gen Loeb-Eiber Filter nd Gen Loeb-Eiber Filter Assembly of 2 nd Gen Filter

14 Schematic of 2 nd Gen Filter Assembly GD source (-450 V, ~1.5 ma) G V G3 +60 V Faraday G4 detector +8 V Applying Dipolar rf to the ~70 pf Filter OrCAD Pspice modelling of rf-transformer Includes estimates of stray capacitance and stray inductance Primary side coil shows resonance frequency at 67.2 MHz Added variable capacitor on primary side to tune circuit Anode +105 V G2 +74 V Mass filter 16 V dc + rf +100 V Electric Potentials 0 V Distance 53 Example Transformer 4 turns on primary side and 4 turns on secondary side, center tapped Amplitude Measured at Filter Input: 4.0 Volt Output: CH Volt CH Volt Phase: 177 degree Maximum amplitude at 68 MHz 14

15 Amplitude Modulation using Tektronix AFG 5 Hz Linear amplitude modulation ramp nd Gen Results at ~0.7 Torr Ar or O 2 rf= 75 MHz, 5 Hz modulation frequency (0-120 mv pp ) through 35 db linear amplifier & transformer Amplitude (V) Time (μs) nd Gen Results at ~0.7 Torr Ar or O 2 rf= 75 MHz, 5 Hz modulation frequency (0-120 mv pp ) through 35 db linear amplifier & transformer. 2 nd Gen Results at ~0.7 Torr Ar or O 2 rf= 75 MHz, 5 Hz modulation frequency (0-120 mv pp ) through 35 db linear amplifier & transformer

16 2 nd Gen Results at ~0.7 Torr Ar or O 2 rf= 75 MHz, 5 Hz modulation frequency (0-120 mv pp ) through 50 db linear amplifier & transformer 3 rd Gen Loeb-Eiber Filter 1 cm rd Generation Loeb-Eiber Filter 3 rd Generation Loeb-Eiber Filter D = 25 m, d = 8 m View from back

17 3 rd Generation Loeb-Eiber Filter 3 rd Generation Loeb-Eiber Filter D = 25 m, d = 8 m D = 25 m, d = 8 m, depth = 25 m rd Generation Loeb-Eiber Filter 3 rd Gen Filter Assembly D = 25 m, d = 8 m, ~260 pf Now same dimensions as Eiber made by hand in 1963! MEMS CAP Inc

18 3 rd Gen Filter Assembly Gold ribbon Gold contact strips Standard push pin connectors th Gen Filter D= 10 µm, d= 10 µm, ~180 pf Theory predicted >50% reduction; observed 35% reduction 4th Gen Filter

19 Conclusions Loeb-Eiber filter can filter ions in single pass in 25 m Operates at low filter potentials (5 V pp, m/z ~50) Derrell Hood Yan An Christine Fisher Acknowledgements Bascom French Paul Schmittauer Coupled with IMS (already done!), could offer superior resolution to stand-alone IMS Simulations show square or round wires are effective Low (thermal) and uniform kinetic energies are best Need dampening gas for drag Prof. Guido Verbeck (UNT) Funding NSF DBI ( ) NSF CAREER ( ) Challenging electronics ~70 MHz into ~300 pf load requires tiny inductor 74 19