Cylindrical Toroidal Ion Trap Mass Spectrometer. Daniel Austin and Nick Taylor Brigham Young University, Provo, Utah

Transcription

1 Cylindrical Toroidal Ion Trap Mass Spectrometer Daniel Austin and Nick Taylor Brigham Young University, Provo, Utah

2 Why miniaturize ion traps Geometrically compact Higher tolerance to pressure Amenable to GC-MS, LC-MS Tandem MS capabilities and how this leads to smaller MS? Smaller traps lead to: Smaller vacuum systems Smaller power supplies Smaller vacuum chamber Faster analysis

3 Issues in miniaturization of ion traps Sensitivity: reduced number of trapped/analyzed ions Arrays of traps Extended trapping dimensions (linear or rectilinear ion traps) Resolution: harder to maintain relative accuracy of electric fields r r +Dr Required Dr to maintain resolution of (m/dm) Mass selected here, m m 4V 2 2 z q r r Mass selected here, m + m Dm 4V Dm z q r Dr r 2 2 r = cm, Dr = 5 microns r = mm, Dr = 5 nm r =. mm, Dr = 5 nm The same is true with arrayed analyzers

4 Simplified electrode shapes for miniaturized ion traps Quadrupole ion trap Cylindrical ion trap Linear ion trap Rectilinear ion trap Toroidal ion trap???

5 The Toroidal Ion Trap Lammert et al, IJMS, 2.

6 Toroidal ion trap requires electrode asymmetry to offset curvature symmetric asymmetric Lammert et al, IJMS, 2.

7 Cylindrical Toroidal Ion Trap Conversion dynode Ejection slit detector RF electrodes Ground and tickle Electrodes are cylindrical surfaces easier to machine or fabricate Asymmetric overlap of electrodes corrects for toroidal curvature Ejected ions focused onto a single point for simplified detection (small EM or Faraday wire) All ions ejected inward

8 Prototype Cylindrical Toroidal Ion Trap Major radius: 3 mm Minor radius: 6 mm RF frequency:.2-2 MHz RF amplitude: <7 V -p

9 Experimental Stability Map of Cylindrical Toroidal Ion Trap This very closely resembles the stability map reported for a RIT with x o = 5. mm, y o = 3.8 mm Slight asymmetry of stability region attributed to two factors: ) Asymmetric electrode spacing x o = 6. mm y o = 5.88 mm 2) Curvature of the trapping volume

10 Stretching electrode spacing to adjust higher-order multipoles Analogous to CIT Stretch direction These dimensions can also be adjusted G. Wu et al. Int. J. Mass Spectrom. 24 (25) All of these dimensions have asymmetric effect on trapping fields

11 % Multipole Component Effect of stretching the RF electrode spacing % Hexapole % Octapole % Decapole % Stretch % Hexapole = -2.3 % % Octapole =. % % Decapole = -3.4 % -2 % Stretch % Hexapole = -2.2 % % Octapole = +.7 % % Decapole = -3.6 % RF Electrode Separation (mm) -5 % Stretch % Hexapole = -2. % % Octapole = +. % % Decapole = -3.7 %

12 Evaluation of Resolution (Δm) of Toluene. % Stretch.6 Toluene. % Stretch Forward Scan m = Toluene. % Stretch Reverse Scan Toluene -2. % Stretch Reverse Scan 2.5 m =.52 Intensity Toluene -5.% Stretch Reverse Scan m = Intensity 85 Intensity m = Reverse Scan Toluene -5. % Stretch Forward Scan.8.2 Intenisty (V) Intensity Toluene -2. % Stretch Forward Scan.4 m = % Stretch Intensity (V) 3 Forward Scan -2. % Stretch.5 m =

13 Mass resolution compares well with other toroidal ion traps Study Trapping Radius (mm) Test Molecule Ion Mass Resolution ( m) Original toroidal IT (Lammert et al.) 7.83 n-butylbenzene Miniaturized toroidal IT (Lammert et al.) 2. n-butylbenzene 9.4 Guardion 7 (Contreras et al.) 2. Toluene 9.42 Halo ion trap 3.5 Toluene 9.3 CTIT 6. Toluene 9.4

14 Normalized Intenstiy Ion Capacity: Effect on Resolution and Mass Accuracy. mtorr.5 mtorr. mtorr.5 mtorr.2 mtorr Reverse Scan mode Resonance ejection used AC = 25 khz, 3.5 Vp-p, 3.25 VDC Can only speak on terms of the sample partial pressure not on the absolute ion populations

15 Other Mass Spectra.8.4 Dichloromethane Intensity Toluene Intenisty (V) Intensity (V) Bromoform

16 Intensity (V) Intensity (V) Intensity (a.u.) Tandem Mass Spectrometry (MS 2 ) of the 34 Molecular Ion of Isobutylbenzene 6 Cooling Ionization Scan Applied Tickle Voltage Cooling Scan 2 Empty Trap Time (ms) CID f = 85 khz V p-p =.5 V

17 Next Step: miniaturized CTIT made from sheet materials Sheet materials (stainless steel, teflon, etc.) available with thickness down to tens of microns excellent uniformity of thickness Inexpensive materials Laser cutting or pressed-stack milling provides high accuracy of shape in 2 dimensions Alignment of individual pieces using jigs Integrated ion guide and ion optics with ¾-circle CTIT Only minor radius needs to be reduced

18 In Conclusion. We have demonstrated a toroidal ion trap mass spectrometer made with cylindrical electrodes Asymmetry of electrode arrangement compensates for toroidal curvature All ions ejected to a single point for improved detection Mass resolution comparable to other toroidal ITs reported in the literature Higher-order multipoles optimized by changing thickness of insulator layers Tandem mass analysis demonstrated Miniaturization facilitated by simplified electrode geometry

19 Questions?