A Dual Split Gate for Improved Ion InjectionMichael W. Senko, Philip M. Remes, Rexford T. Heller Thermo Fisher Scientific, San Jose, CA

2 A Dual Split Gate for Improved Ion Injection

A Dual Split Gate for Improved Ion Injection Michael W. Senko, Philip M. Remes, Rexford T. Heller Thermo Fisher Scientific, San Jose, CA

Conclusion Linear injection behavior is critical in order to accurately fill ion traps.

Standard deflecting gates behave non-linearly at short injection times.

A dual gate can provide linear behavior, even at injection times that are shorter than the time of flight across the gate.

References 1. Senko, M. W. Method and apparatus for a dual gate for a mass spectrometer.

U.S. Patent 8,026,475, Sep 27, 2011.

2. Schwartz, J. C.; Zhou, X. G.; Bier, M. E. Method and apparatus of increasing dynamic range and sensitivity of a mass spectrometer. U.S. Patent 5,572,022, Nov 5, 1996.

Overview Purpose: Reduce mass dependency for short injection times

Methods: Ion optics simulation of concept and measurement of mass dependency in single and dual gate modes

Results: Dual gate mode shows significantly reduced mass dependencies, particularly at injection times < 10 usec

Introduction Accurate and precise control of injection is critical for trapped ion analyzers such as linear ion traps and Orbitraps. When too few ions are injected, sensitivity and dynamic range suffer, and when too many ions are injected, various space charge effects can be observed, such as resolution and mass accuracy degradation.

Gating for trapped ion instruments is most commonly performed with either a retarding or a deflecting lens. A deflecting lens is preferable because it eliminates the possibility of unintended trapping of ions in the RF multipole immediately upstream of the gate. Deflecting gates exhibit performance issues when the injection time approaches either the slew time of the gating supply or the ion flight time across the gate, whichever is longer.

With modern electronics, a 50 V deflection voltage can be switched in ~100 nsec, so the limitation to deflecting gates is almost always the gate flight time. A 1000 m/z ion with 10 eV/q of kinetic energy moves with a velocity of 1 mm/usec, so the flight across a 6 mm gate is ~6 usec. This time can only be shortened by decreasing the gate length or increasing the kinetic energy. Either of these solutions requires an increased deflection voltage, which makes the power supply design more complex.

With the use of two back-to-back gates operated in an appropriate fashion1, the limitation is not the time it takes to fly across either gate, but instead the time it takes to fly between the gates. Since the space between the gates can be ~10× shorter than the length of either gate, the injection time limitations can be reduced a similar amount.

Methods Simulation

All simulations were performed with SIMION® 8.1 software. Gate timing is implemented with RPN User Programs.

Mass Spectrometry

All experimental data was generated using a Thermo Scientific™ Orbitrap Fusion™ Tribrid™ mass spectrometer. The optics were unmodified from the standard instrument. Switching between single and double gate modes was done by changing the sequence of applied voltages.

FIGURE 1. Rendering of the double gate, located between the mass resolving quadrupole and transfer octapole.

Results Concept

Although a double gate is twice the length of a single gate and requires twice the flight time to cross, when operated appropriately, performance is not restricted by the flight time across either gate, but by the flight time between the gates. As shown in Figure 2, while in the pre-injection phase, ions are allowed to cross the open front gate and are then deflected by the closed rear gate. In the injection phase, the rear gate is opened, allowing ions to pass through to the downstream optics. In the post-injection phase, the front gate is closed, deflecting any ions that have not already transitioned to the rear gate.

Mass Bias

Due to the mass dependence of the flight time across the gate, short injection times can result in severe mass bias. Figure 4 compares spectra of the Orbitrap Fusion calibration mixture with a 10 usec injection period using single gate and a double gate modes. Since this injection time approaches the flight time across the gate for larger ions, significant attenuation can be observed. Although the loss at m/z 195 is only 15%, at m/z 1022 there is a 75% loss, and at m/z 1822 the loss is >95%.

SIMION is a registered trademark of Scientific Instrument Services, Inc. All other trademarks are the property of Thermo Fisher Scientific and its subsidiaries.

This information is not intended to encourage use of these products in any manners that might infringe the intellectual property rights of others.

PO64113-EN 0614S

FIGURE 3. Simulation of single gate and double gate modes. 10 usec gate for 1000 m/z ions with 10 eV.

FIGURE 5. Plots of injection time versus signal for various masses in single gate and double gate modes.

FIGURE 8. Plot of injection time versus normalized ion signal for single and double gate modes.

Simulation

For all simulations, ions started with 1 usec separations, so 10 ions would be expected to traverse when the gate time is 10 usec. Figure 3 demonstrates the problem with traditional deflecting gates when the gate time approaches the flight time across the gate. Although the gate is open for 10 usec, only 6 ions cross the gate, and half these do so with modulated (> 1eV) kinetic energies that are unfavorable for subsequent trapping. For the dual gate, 10 ions cross the gate in 10 usec, with only 2 having unfavorable kinetic energy modulation.

Injection Linearity

Critical to performance for all trapped ion instruments is the assumption that the number of ions accumulated is directly proportional to the injection time. If this assumption is not true, it is difficult to accurately fill the ion trap. This assumption can be tested by looking at the signal of various ions as a function of injection time. As shown in Figure 5, when operating in single gate mode, there is a clear onset time before any signal is observed. Figure 6 shows that this onset is mass dependent, and therefore not easily corrected. When operating in double gate mode, there is still an onset period, but this is very uniform, and therefore easily corrected.

FIGURE 2. Cartoon of dual gate operation.

Injection

0 0

0 0 Post-Injection

0 +

0 0 Pre-Injection

0 0

+ 0

FIGURE 4. Spectra from 10 usec injection periods using single gate and double gate mode.

DoubleGate #1-10 RT: 0.00-0.11 AV: 10 NL: 1.00E1T: ITMS + p ESI Full ms [150.00-2000.00]

500 1000 1500 2000m/z

05

101520253035404550556065707580859095

100

Rel

ativ

e Ab

unda

nce

1321.90

1521.87

1221.87

1621.83

1121.871721.83

195.03

1821.831021.90262.53 524.20

1921.67537.83268.90921.93825.93

Double Gate

FIGURE 6. Plot of onset time versus mass for single and double gate modes.

Single Gate

Double Gate

Implications for Automatic Gain Control

Some form of automatic gain control2 is used for all trapped ion instruments to ensure an acceptable dynamic range while avoiding potential space charge effects and detector saturation. AGC works by measuring the total ion signal at a known injection time (the prescan) and then calculating an appropriate injection time for the analytical scan assuming a linear accumulation of ions. Without a linear accumulation of ions, it is not possible to accurately fill the ion trap for the analytical scan. Figure 7 shows the double gate mode provides a much more proportional relationship between injection time and total ion signal. This is more clearly shown in Figure 8, where the total ion signal is normalized by dividing by the injection time. For the double gate mode, the normalized signal is essentially constant, while the singles gate normalized signal begins to deviate at times less than ~80 usec.

FIGURE 7. Plot of injection time versus total ion signal for single and double gate modes.

SingleGate #1-10 RT: 0.00-0.11 AV: 10 NL: 1.00E1T: ITMS + p ESI Full ms [150.00-2000.00]

500 1000 1500 2000m/z

05

101520253035404550556065707580859095

100

Rel

ativ

e Ab

unda

nce

195.00

1221.901421.83

262.53 1521.83524.20 1021.87 1621.83537.73268.90 883.83 1786.60

Single Gate

–15% –75% –95%

0V

0V

0V

0V –50V

50/0/0V

0/0/50V

Double Gate

5 mm

0V

0V

0V

0V 0V

50/0/50V

–50V

6 mm 6 mm

Single Gate

3Thermo Scientific Poster Note • PN-64113-ASMS-EN-0614S

A Dual Split Gate for Improved Ion Injection Michael W. Senko, Philip M. Remes, Rexford T. Heller Thermo Fisher Scientific, San Jose, CA

Conclusion Linear injection behavior is critical in order to accurately fill ion traps.

Standard deflecting gates behave non-linearly at short injection times.

A dual gate can provide linear behavior, even at injection times that are shorter than the time of flight across the gate.

References 1. Senko, M. W. Method and apparatus for a dual gate for a mass spectrometer.

U.S. Patent 8,026,475, Sep 27, 2011.

2. Schwartz, J. C.; Zhou, X. G.; Bier, M. E. Method and apparatus of increasing dynamic range and sensitivity of a mass spectrometer. U.S. Patent 5,572,022, Nov 5, 1996.

Overview Purpose: Reduce mass dependency for short injection times

Methods: Ion optics simulation of concept and measurement of mass dependency in single and dual gate modes

Results: Dual gate mode shows significantly reduced mass dependencies, particularly at injection times < 10 usec

Introduction Accurate and precise control of injection is critical for trapped ion analyzers such as linear ion traps and Orbitraps. When too few ions are injected, sensitivity and dynamic range suffer, and when too many ions are injected, various space charge effects can be observed, such as resolution and mass accuracy degradation.

Gating for trapped ion instruments is most commonly performed with either a retarding or a deflecting lens. A deflecting lens is preferable because it eliminates the possibility of unintended trapping of ions in the RF multipole immediately upstream of the gate. Deflecting gates exhibit performance issues when the injection time approaches either the slew time of the gating supply or the ion flight time across the gate, whichever is longer.

With modern electronics, a 50 V deflection voltage can be switched in ~100 nsec, so the limitation to deflecting gates is almost always the gate flight time. A 1000 m/z ion with 10 eV/q of kinetic energy moves with a velocity of 1 mm/usec, so the flight across a 6 mm gate is ~6 usec. This time can only be shortened by decreasing the gate length or increasing the kinetic energy. Either of these solutions requires an increased deflection voltage, which makes the power supply design more complex.

With the use of two back-to-back gates operated in an appropriate fashion1, the limitation is not the time it takes to fly across either gate, but instead the time it takes to fly between the gates. Since the space between the gates can be ~10× shorter than the length of either gate, the injection time limitations can be reduced a similar amount.

Methods Simulation

All simulations were performed with SIMION® 8.1 software. Gate timing is implemented with RPN User Programs.

Mass Spectrometry

All experimental data was generated using a Thermo Scientific™ Orbitrap Fusion™ Tribrid™ mass spectrometer. The optics were unmodified from the standard instrument. Switching between single and double gate modes was done by changing the sequence of applied voltages.

FIGURE 1. Rendering of the double gate, located between the mass resolving quadrupole and transfer octapole.

Results Concept

Although a double gate is twice the length of a single gate and requires twice the flight time to cross, when operated appropriately, performance is not restricted by the flight time across either gate, but by the flight time between the gates. As shown in Figure 2, while in the pre-injection phase, ions are allowed to cross the open front gate and are then deflected by the closed rear gate. In the injection phase, the rear gate is opened, allowing ions to pass through to the downstream optics. In the post-injection phase, the front gate is closed, deflecting any ions that have not already transitioned to the rear gate.

Mass Bias

Due to the mass dependence of the flight time across the gate, short injection times can result in severe mass bias. Figure 4 compares spectra of the Orbitrap Fusion calibration mixture with a 10 usec injection period using single gate and a double gate modes. Since this injection time approaches the flight time across the gate for larger ions, significant attenuation can be observed. Although the loss at m/z 195 is only 15%, at m/z 1022 there is a 75% loss, and at m/z 1822 the loss is >95%.

SIMION is a registered trademark of Scientific Instrument Services, Inc. All other trademarks are the property of Thermo Fisher Scientific and its subsidiaries.

This information is not intended to encourage use of these products in any manners that might infringe the intellectual property rights of others.

PO64113-EN 0614S

FIGURE 3. Simulation of single gate and double gate modes. 10 usec gate for 1000 m/z ions with 10 eV.

FIGURE 5. Plots of injection time versus signal for various masses in single gate and double gate modes.

FIGURE 8. Plot of injection time versus normalized ion signal for single and double gate modes.

Simulation

For all simulations, ions started with 1 usec separations, so 10 ions would be expected to traverse when the gate time is 10 usec. Figure 3 demonstrates the problem with traditional deflecting gates when the gate time approaches the flight time across the gate. Although the gate is open for 10 usec, only 6 ions cross the gate, and half these do so with modulated (> 1eV) kinetic energies that are unfavorable for subsequent trapping. For the dual gate, 10 ions cross the gate in 10 usec, with only 2 having unfavorable kinetic energy modulation.

Injection Linearity

Critical to performance for all trapped ion instruments is the assumption that the number of ions accumulated is directly proportional to the injection time. If this assumption is not true, it is difficult to accurately fill the ion trap. This assumption can be tested by looking at the signal of various ions as a function of injection time. As shown in Figure 5, when operating in single gate mode, there is a clear onset time before any signal is observed. Figure 6 shows that this onset is mass dependent, and therefore not easily corrected. When operating in double gate mode, there is still an onset period, but this is very uniform, and therefore easily corrected.

FIGURE 2. Cartoon of dual gate operation.

Injection

0 0

0 0 Post-Injection

0 +

0 0 Pre-Injection

0 0

+ 0

FIGURE 4. Spectra from 10 usec injection periods using single gate and double gate mode.

DoubleGate #1-10 RT: 0.00-0.11 AV: 10 NL: 1.00E1T: ITMS + p ESI Full ms [150.00-2000.00]

500 1000 1500 2000m/z

05

101520253035404550556065707580859095

100

Rel

ativ

e Ab

unda

nce

1321.90

1521.87

1221.87

1621.83

1121.871721.83

195.03

1821.831021.90262.53 524.20

1921.67537.83268.90921.93825.93

Double Gate

FIGURE 6. Plot of onset time versus mass for single and double gate modes.

Single Gate

Double Gate

Implications for Automatic Gain Control

Some form of automatic gain control2 is used for all trapped ion instruments to ensure an acceptable dynamic range while avoiding potential space charge effects and detector saturation. AGC works by measuring the total ion signal at a known injection time (the prescan) and then calculating an appropriate injection time for the analytical scan assuming a linear accumulation of ions. Without a linear accumulation of ions, it is not possible to accurately fill the ion trap for the analytical scan. Figure 7 shows the double gate mode provides a much more proportional relationship between injection time and total ion signal. This is more clearly shown in Figure 8, where the total ion signal is normalized by dividing by the injection time. For the double gate mode, the normalized signal is essentially constant, while the singles gate normalized signal begins to deviate at times less than ~80 usec.

FIGURE 7. Plot of injection time versus total ion signal for single and double gate modes.

SingleGate #1-10 RT: 0.00-0.11 AV: 10 NL: 1.00E1T: ITMS + p ESI Full ms [150.00-2000.00]

500 1000 1500 2000m/z

05

101520253035404550556065707580859095

100

Rel

ativ

e Ab

unda

nce

195.00

1221.901421.83

262.53 1521.83524.20 1021.87 1621.83537.73268.90 883.83 1786.60

Single Gate

–15% –75% –95%

0V

0V

0V

0V –50V

50/0/0V

0/0/50V

Double Gate

5 mm

0V

0V

0V

0V 0V

50/0/50V

–50V

6 mm 6 mm

Single Gate

4 A Dual Split Gate for Improved Ion Injection

A Dual Split Gate for Improved Ion Injection Michael W. Senko, Philip M. Remes, Rexford T. Heller Thermo Fisher Scientific, San Jose, CA

Conclusion Linear injection behavior is critical in order to accurately fill ion traps.

Standard deflecting gates behave non-linearly at short injection times.

A dual gate can provide linear behavior, even at injection times that are shorter than the time of flight across the gate.

References 1. Senko, M. W. Method and apparatus for a dual gate for a mass spectrometer.

U.S. Patent 8,026,475, Sep 27, 2011.

2. Schwartz, J. C.; Zhou, X. G.; Bier, M. E. Method and apparatus of increasing dynamic range and sensitivity of a mass spectrometer. U.S. Patent 5,572,022, Nov 5, 1996.

Overview Purpose: Reduce mass dependency for short injection times

Methods: Ion optics simulation of concept and measurement of mass dependency in single and dual gate modes

Results: Dual gate mode shows significantly reduced mass dependencies, particularly at injection times < 10 usec

Introduction Accurate and precise control of injection is critical for trapped ion analyzers such as linear ion traps and Orbitraps. When too few ions are injected, sensitivity and dynamic range suffer, and when too many ions are injected, various space charge effects can be observed, such as resolution and mass accuracy degradation.

Gating for trapped ion instruments is most commonly performed with either a retarding or a deflecting lens. A deflecting lens is preferable because it eliminates the possibility of unintended trapping of ions in the RF multipole immediately upstream of the gate. Deflecting gates exhibit performance issues when the injection time approaches either the slew time of the gating supply or the ion flight time across the gate, whichever is longer.

With modern electronics, a 50 V deflection voltage can be switched in ~100 nsec, so the limitation to deflecting gates is almost always the gate flight time. A 1000 m/z ion with 10 eV/q of kinetic energy moves with a velocity of 1 mm/usec, so the flight across a 6 mm gate is ~6 usec. This time can only be shortened by decreasing the gate length or increasing the kinetic energy. Either of these solutions requires an increased deflection voltage, which makes the power supply design more complex.

With the use of two back-to-back gates operated in an appropriate fashion1, the limitation is not the time it takes to fly across either gate, but instead the time it takes to fly between the gates. Since the space between the gates can be ~10× shorter than the length of either gate, the injection time limitations can be reduced a similar amount.

Methods Simulation

All simulations were performed with SIMION® 8.1 software. Gate timing is implemented with RPN User Programs.

Mass Spectrometry

All experimental data was generated using a Thermo Scientific™ Orbitrap Fusion™ Tribrid™ mass spectrometer. The optics were unmodified from the standard instrument. Switching between single and double gate modes was done by changing the sequence of applied voltages.

FIGURE 1. Rendering of the double gate, located between the mass resolving quadrupole and transfer octapole.

Results Concept

Although a double gate is twice the length of a single gate and requires twice the flight time to cross, when operated appropriately, performance is not restricted by the flight time across either gate, but by the flight time between the gates. As shown in Figure 2, while in the pre-injection phase, ions are allowed to cross the open front gate and are then deflected by the closed rear gate. In the injection phase, the rear gate is opened, allowing ions to pass through to the downstream optics. In the post-injection phase, the front gate is closed, deflecting any ions that have not already transitioned to the rear gate.

Mass Bias

Due to the mass dependence of the flight time across the gate, short injection times can result in severe mass bias. Figure 4 compares spectra of the Orbitrap Fusion calibration mixture with a 10 usec injection period using single gate and a double gate modes. Since this injection time approaches the flight time across the gate for larger ions, significant attenuation can be observed. Although the loss at m/z 195 is only 15%, at m/z 1022 there is a 75% loss, and at m/z 1822 the loss is >95%.

SIMION is a registered trademark of Scientific Instrument Services, Inc. All other trademarks are the property of Thermo Fisher Scientific and its subsidiaries.

This information is not intended to encourage use of these products in any manners that might infringe the intellectual property rights of others.

PO64113-EN 0614S

FIGURE 3. Simulation of single gate and double gate modes. 10 usec gate for 1000 m/z ions with 10 eV.

FIGURE 5. Plots of injection time versus signal for various masses in single gate and double gate modes.

FIGURE 8. Plot of injection time versus normalized ion signal for single and double gate modes.

Simulation

For all simulations, ions started with 1 usec separations, so 10 ions would be expected to traverse when the gate time is 10 usec. Figure 3 demonstrates the problem with traditional deflecting gates when the gate time approaches the flight time across the gate. Although the gate is open for 10 usec, only 6 ions cross the gate, and half these do so with modulated (> 1eV) kinetic energies that are unfavorable for subsequent trapping. For the dual gate, 10 ions cross the gate in 10 usec, with only 2 having unfavorable kinetic energy modulation.

Injection Linearity

Critical to performance for all trapped ion instruments is the assumption that the number of ions accumulated is directly proportional to the injection time. If this assumption is not true, it is difficult to accurately fill the ion trap. This assumption can be tested by looking at the signal of various ions as a function of injection time. As shown in Figure 5, when operating in single gate mode, there is a clear onset time before any signal is observed. Figure 6 shows that this onset is mass dependent, and therefore not easily corrected. When operating in double gate mode, there is still an onset period, but this is very uniform, and therefore easily corrected.

FIGURE 2. Cartoon of dual gate operation.

Injection

0 0

0 0 Post-Injection

0 +

0 0 Pre-Injection

0 0

+ 0

FIGURE 4. Spectra from 10 usec injection periods using single gate and double gate mode.

DoubleGate #1-10 RT: 0.00-0.11 AV: 10 NL: 1.00E1T: ITMS + p ESI Full ms [150.00-2000.00]

500 1000 1500 2000m/z

05

101520253035404550556065707580859095

100

Rel

ativ

e Ab

unda

nce

1321.90

1521.87

1221.87

1621.83

1121.871721.83

195.03

1821.831021.90262.53 524.20

1921.67537.83268.90921.93825.93

Double Gate

FIGURE 6. Plot of onset time versus mass for single and double gate modes.

Single Gate

Double Gate

Implications for Automatic Gain Control

Some form of automatic gain control2 is used for all trapped ion instruments to ensure an acceptable dynamic range while avoiding potential space charge effects and detector saturation. AGC works by measuring the total ion signal at a known injection time (the prescan) and then calculating an appropriate injection time for the analytical scan assuming a linear accumulation of ions. Without a linear accumulation of ions, it is not possible to accurately fill the ion trap for the analytical scan. Figure 7 shows the double gate mode provides a much more proportional relationship between injection time and total ion signal. This is more clearly shown in Figure 8, where the total ion signal is normalized by dividing by the injection time. For the double gate mode, the normalized signal is essentially constant, while the singles gate normalized signal begins to deviate at times less than ~80 usec.

FIGURE 7. Plot of injection time versus total ion signal for single and double gate modes.

SingleGate #1-10 RT: 0.00-0.11 AV: 10 NL: 1.00E1T: ITMS + p ESI Full ms [150.00-2000.00]

500 1000 1500 2000m/z

05

101520253035404550556065707580859095

100

Rel

ativ

e Ab

unda

nce

195.00

1221.901421.83

262.53 1521.83524.20 1021.87 1621.83537.73268.90 883.83 1786.60

Single Gate

–15% –75% –95%

0V

0V

0V

0V –50V

50/0/0V

0/0/50V

Double Gate

5 mm

0V

0V

0V

0V 0V

50/0/50V

–50V

6 mm 6 mm

Single Gate

5Thermo Scientific Poster Note • PN-64113-ASMS-EN-0614S

A Dual Split Gate for Improved Ion Injection Michael W. Senko, Philip M. Remes, Rexford T. Heller Thermo Fisher Scientific, San Jose, CA

Conclusion Linear injection behavior is critical in order to accurately fill ion traps.

Standard deflecting gates behave non-linearly at short injection times.

A dual gate can provide linear behavior, even at injection times that are shorter than the time of flight across the gate.

References 1. Senko, M. W. Method and apparatus for a dual gate for a mass spectrometer.

U.S. Patent 8,026,475, Sep 27, 2011.

2. Schwartz, J. C.; Zhou, X. G.; Bier, M. E. Method and apparatus of increasing dynamic range and sensitivity of a mass spectrometer. U.S. Patent 5,572,022, Nov 5, 1996.

Overview Purpose: Reduce mass dependency for short injection times

Methods: Ion optics simulation of concept and measurement of mass dependency in single and dual gate modes

Results: Dual gate mode shows significantly reduced mass dependencies, particularly at injection times < 10 usec

Introduction Accurate and precise control of injection is critical for trapped ion analyzers such as linear ion traps and Orbitraps. When too few ions are injected, sensitivity and dynamic range suffer, and when too many ions are injected, various space charge effects can be observed, such as resolution and mass accuracy degradation.

Gating for trapped ion instruments is most commonly performed with either a retarding or a deflecting lens. A deflecting lens is preferable because it eliminates the possibility of unintended trapping of ions in the RF multipole immediately upstream of the gate. Deflecting gates exhibit performance issues when the injection time approaches either the slew time of the gating supply or the ion flight time across the gate, whichever is longer.

With modern electronics, a 50 V deflection voltage can be switched in ~100 nsec, so the limitation to deflecting gates is almost always the gate flight time. A 1000 m/z ion with 10 eV/q of kinetic energy moves with a velocity of 1 mm/usec, so the flight across a 6 mm gate is ~6 usec. This time can only be shortened by decreasing the gate length or increasing the kinetic energy. Either of these solutions requires an increased deflection voltage, which makes the power supply design more complex.

With the use of two back-to-back gates operated in an appropriate fashion1, the limitation is not the time it takes to fly across either gate, but instead the time it takes to fly between the gates. Since the space between the gates can be ~10× shorter than the length of either gate, the injection time limitations can be reduced a similar amount.

Methods Simulation

All simulations were performed with SIMION® 8.1 software. Gate timing is implemented with RPN User Programs.

Mass Spectrometry

All experimental data was generated using a Thermo Scientific™ Orbitrap Fusion™ Tribrid™ mass spectrometer. The optics were unmodified from the standard instrument. Switching between single and double gate modes was done by changing the sequence of applied voltages.

FIGURE 1. Rendering of the double gate, located between the mass resolving quadrupole and transfer octapole.

Results Concept

Although a double gate is twice the length of a single gate and requires twice the flight time to cross, when operated appropriately, performance is not restricted by the flight time across either gate, but by the flight time between the gates. As shown in Figure 2, while in the pre-injection phase, ions are allowed to cross the open front gate and are then deflected by the closed rear gate. In the injection phase, the rear gate is opened, allowing ions to pass through to the downstream optics. In the post-injection phase, the front gate is closed, deflecting any ions that have not already transitioned to the rear gate.

Mass Bias

Due to the mass dependence of the flight time across the gate, short injection times can result in severe mass bias. Figure 4 compares spectra of the Orbitrap Fusion calibration mixture with a 10 usec injection period using single gate and a double gate modes. Since this injection time approaches the flight time across the gate for larger ions, significant attenuation can be observed. Although the loss at m/z 195 is only 15%, at m/z 1022 there is a 75% loss, and at m/z 1822 the loss is >95%.

SIMION is a registered trademark of Scientific Instrument Services, Inc. All other trademarks are the property of Thermo Fisher Scientific and its subsidiaries.

This information is not intended to encourage use of these products in any manners that might infringe the intellectual property rights of others.

PO64113-EN 0614S

FIGURE 3. Simulation of single gate and double gate modes. 10 usec gate for 1000 m/z ions with 10 eV.

FIGURE 5. Plots of injection time versus signal for various masses in single gate and double gate modes.

FIGURE 8. Plot of injection time versus normalized ion signal for single and double gate modes.

Simulation

For all simulations, ions started with 1 usec separations, so 10 ions would be expected to traverse when the gate time is 10 usec. Figure 3 demonstrates the problem with traditional deflecting gates when the gate time approaches the flight time across the gate. Although the gate is open for 10 usec, only 6 ions cross the gate, and half these do so with modulated (> 1eV) kinetic energies that are unfavorable for subsequent trapping. For the dual gate, 10 ions cross the gate in 10 usec, with only 2 having unfavorable kinetic energy modulation.

Injection Linearity

Critical to performance for all trapped ion instruments is the assumption that the number of ions accumulated is directly proportional to the injection time. If this assumption is not true, it is difficult to accurately fill the ion trap. This assumption can be tested by looking at the signal of various ions as a function of injection time. As shown in Figure 5, when operating in single gate mode, there is a clear onset time before any signal is observed. Figure 6 shows that this onset is mass dependent, and therefore not easily corrected. When operating in double gate mode, there is still an onset period, but this is very uniform, and therefore easily corrected.

FIGURE 2. Cartoon of dual gate operation.

Injection

0 0

0 0 Post-Injection

0 +

0 0 Pre-Injection

0 0

+ 0

FIGURE 4. Spectra from 10 usec injection periods using single gate and double gate mode.

DoubleGate #1-10 RT: 0.00-0.11 AV: 10 NL: 1.00E1T: ITMS + p ESI Full ms [150.00-2000.00]

500 1000 1500 2000m/z

05

101520253035404550556065707580859095

100

Rel

ativ

e Ab

unda

nce

1321.90

1521.87

1221.87

1621.83

1121.871721.83

195.03

1821.831021.90262.53 524.20

1921.67537.83268.90921.93825.93

Double Gate

FIGURE 6. Plot of onset time versus mass for single and double gate modes.

Single Gate

Double Gate

Implications for Automatic Gain Control

Some form of automatic gain control2 is used for all trapped ion instruments to ensure an acceptable dynamic range while avoiding potential space charge effects and detector saturation. AGC works by measuring the total ion signal at a known injection time (the prescan) and then calculating an appropriate injection time for the analytical scan assuming a linear accumulation of ions. Without a linear accumulation of ions, it is not possible to accurately fill the ion trap for the analytical scan. Figure 7 shows the double gate mode provides a much more proportional relationship between injection time and total ion signal. This is more clearly shown in Figure 8, where the total ion signal is normalized by dividing by the injection time. For the double gate mode, the normalized signal is essentially constant, while the singles gate normalized signal begins to deviate at times less than ~80 usec.

FIGURE 7. Plot of injection time versus total ion signal for single and double gate modes.

SingleGate #1-10 RT: 0.00-0.11 AV: 10 NL: 1.00E1T: ITMS + p ESI Full ms [150.00-2000.00]

500 1000 1500 2000m/z

05

101520253035404550556065707580859095

100

Rel

ativ

e Ab

unda

nce

195.00

1221.901421.83

262.53 1521.83524.20 1021.87 1621.83537.73268.90 883.83 1786.60

Single Gate

–15% –75% –95%

0V

0V

0V

0V –50V

50/0/0V

0/0/50V

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5 mm

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6 mm 6 mm

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6 A Dual Split Gate for Improved Ion Injection

A Dual Split Gate for Improved Ion Injection Michael W. Senko, Philip M. Remes, Rexford T. Heller Thermo Fisher Scientific, San Jose, CA

Conclusion Linear injection behavior is critical in order to accurately fill ion traps.

Standard deflecting gates behave non-linearly at short injection times.

A dual gate can provide linear behavior, even at injection times that are shorter than the time of flight across the gate.

References 1. Senko, M. W. Method and apparatus for a dual gate for a mass spectrometer.

U.S. Patent 8,026,475, Sep 27, 2011.

2. Schwartz, J. C.; Zhou, X. G.; Bier, M. E. Method and apparatus of increasing dynamic range and sensitivity of a mass spectrometer. U.S. Patent 5,572,022, Nov 5, 1996.

Overview Purpose: Reduce mass dependency for short injection times

Methods: Ion optics simulation of concept and measurement of mass dependency in single and dual gate modes

Results: Dual gate mode shows significantly reduced mass dependencies, particularly at injection times < 10 usec

Introduction Accurate and precise control of injection is critical for trapped ion analyzers such as linear ion traps and Orbitraps. When too few ions are injected, sensitivity and dynamic range suffer, and when too many ions are injected, various space charge effects can be observed, such as resolution and mass accuracy degradation.

Gating for trapped ion instruments is most commonly performed with either a retarding or a deflecting lens. A deflecting lens is preferable because it eliminates the possibility of unintended trapping of ions in the RF multipole immediately upstream of the gate. Deflecting gates exhibit performance issues when the injection time approaches either the slew time of the gating supply or the ion flight time across the gate, whichever is longer.

With modern electronics, a 50 V deflection voltage can be switched in ~100 nsec, so the limitation to deflecting gates is almost always the gate flight time. A 1000 m/z ion with 10 eV/q of kinetic energy moves with a velocity of 1 mm/usec, so the flight across a 6 mm gate is ~6 usec. This time can only be shortened by decreasing the gate length or increasing the kinetic energy. Either of these solutions requires an increased deflection voltage, which makes the power supply design more complex.

With the use of two back-to-back gates operated in an appropriate fashion1, the limitation is not the time it takes to fly across either gate, but instead the time it takes to fly between the gates. Since the space between the gates can be ~10× shorter than the length of either gate, the injection time limitations can be reduced a similar amount.

Methods Simulation

All simulations were performed with SIMION® 8.1 software. Gate timing is implemented with RPN User Programs.

Mass Spectrometry

All experimental data was generated using a Thermo Scientific™ Orbitrap Fusion™ Tribrid™ mass spectrometer. The optics were unmodified from the standard instrument. Switching between single and double gate modes was done by changing the sequence of applied voltages.

FIGURE 1. Rendering of the double gate, located between the mass resolving quadrupole and transfer octapole.

Results Concept

Although a double gate is twice the length of a single gate and requires twice the flight time to cross, when operated appropriately, performance is not restricted by the flight time across either gate, but by the flight time between the gates. As shown in Figure 2, while in the pre-injection phase, ions are allowed to cross the open front gate and are then deflected by the closed rear gate. In the injection phase, the rear gate is opened, allowing ions to pass through to the downstream optics. In the post-injection phase, the front gate is closed, deflecting any ions that have not already transitioned to the rear gate.

Mass Bias

Due to the mass dependence of the flight time across the gate, short injection times can result in severe mass bias. Figure 4 compares spectra of the Orbitrap Fusion calibration mixture with a 10 usec injection period using single gate and a double gate modes. Since this injection time approaches the flight time across the gate for larger ions, significant attenuation can be observed. Although the loss at m/z 195 is only 15%, at m/z 1022 there is a 75% loss, and at m/z 1822 the loss is >95%.

SIMION is a registered trademark of Scientific Instrument Services, Inc. All other trademarks are the property of Thermo Fisher Scientific and its subsidiaries.

This information is not intended to encourage use of these products in any manners that might infringe the intellectual property rights of others.

PO64113-EN 0614S

FIGURE 3. Simulation of single gate and double gate modes. 10 usec gate for 1000 m/z ions with 10 eV.

FIGURE 5. Plots of injection time versus signal for various masses in single gate and double gate modes.

FIGURE 8. Plot of injection time versus normalized ion signal for single and double gate modes.

Simulation

For all simulations, ions started with 1 usec separations, so 10 ions would be expected to traverse when the gate time is 10 usec. Figure 3 demonstrates the problem with traditional deflecting gates when the gate time approaches the flight time across the gate. Although the gate is open for 10 usec, only 6 ions cross the gate, and half these do so with modulated (> 1eV) kinetic energies that are unfavorable for subsequent trapping. For the dual gate, 10 ions cross the gate in 10 usec, with only 2 having unfavorable kinetic energy modulation.

Injection Linearity

Critical to performance for all trapped ion instruments is the assumption that the number of ions accumulated is directly proportional to the injection time. If this assumption is not true, it is difficult to accurately fill the ion trap. This assumption can be tested by looking at the signal of various ions as a function of injection time. As shown in Figure 5, when operating in single gate mode, there is a clear onset time before any signal is observed. Figure 6 shows that this onset is mass dependent, and therefore not easily corrected. When operating in double gate mode, there is still an onset period, but this is very uniform, and therefore easily corrected.

FIGURE 2. Cartoon of dual gate operation.

Injection

0 0

0 0 Post-Injection

0 +

0 0 Pre-Injection

0 0

+ 0

FIGURE 4. Spectra from 10 usec injection periods using single gate and double gate mode.

DoubleGate #1-10 RT: 0.00-0.11 AV: 10 NL: 1.00E1T: ITMS + p ESI Full ms [150.00-2000.00]

500 1000 1500 2000m/z

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1521.87

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195.03

1821.831021.90262.53 524.20

1921.67537.83268.90921.93825.93

Double Gate

FIGURE 6. Plot of onset time versus mass for single and double gate modes.

Single Gate

Double Gate

Implications for Automatic Gain Control

Some form of automatic gain control2 is used for all trapped ion instruments to ensure an acceptable dynamic range while avoiding potential space charge effects and detector saturation. AGC works by measuring the total ion signal at a known injection time (the prescan) and then calculating an appropriate injection time for the analytical scan assuming a linear accumulation of ions. Without a linear accumulation of ions, it is not possible to accurately fill the ion trap for the analytical scan. Figure 7 shows the double gate mode provides a much more proportional relationship between injection time and total ion signal. This is more clearly shown in Figure 8, where the total ion signal is normalized by dividing by the injection time. For the double gate mode, the normalized signal is essentially constant, while the singles gate normalized signal begins to deviate at times less than ~80 usec.

FIGURE 7. Plot of injection time versus total ion signal for single and double gate modes.

SingleGate #1-10 RT: 0.00-0.11 AV: 10 NL: 1.00E1T: ITMS + p ESI Full ms [150.00-2000.00]

500 1000 1500 2000m/z

05

101520253035404550556065707580859095

100

Rel

ativ

e Ab

unda

nce

195.00

1221.901421.83

262.53 1521.83524.20 1021.87 1621.83537.73268.90 883.83 1786.60

Single Gate

–15% –75% –95%

0V

0V

0V

0V –50V

50/0/0V

0/0/50V

Double Gate

5 mm

0V

0V

0V

0V 0V

50/0/50V

–50V

6 mm 6 mm

Single Gate

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