ION MOBILITY SPECTROMETER

Abstract

An offset voltage adjusting portion is provided in an amplifying portion for applying respective pulse voltages to a pair of grid electrodes that structures a shutter gate grid. Because the pulse voltage is shifted in the direction of the voltage axis, with the amplitude and pulse width thereof maintained, when the offset voltage is adjusted, this enables a potential difference to be applied to the voltages that are applied to the front grid electrode and the rear grid electrode when the shutter gate grid is open. This potential difference produces an electric field for accelerating ions in the space between the pair of grid electrodes, thus accelerating the movement of ions immediately following the switching of the shutter gate grid from the closed state to the open state, enabling the pulse width of the ions to be narrowed.

Claims

1. An ion mobility spectrometer, having an ionizing portion for generating sample component derivative ions, and a drift region in order to cause ions, generated by the ionizing portion, to move in order to separate the depending on mobility, comprising: a) a shutter gate grid comprising a front grid electrode and a rear grid electrode disposed with a prescribed distance of separation in the direction of movement of the ions, between the ionizing portion and the drift region, in order to cut off or feed the ions into the drift region with short pulses; and b) a gate grid controlling portion for applying, to the rear grid electrode, a voltage that is higher than that of the front grid electrode, so as to form an electropotential barrier to the ions in the space between the front grid electrode and the rear grid electrode when cutting off the ions with the shutter grid gate, and for applying, to the front grid electrode, a voltage that is higher than that of the rear grid electrode, so as to form an electric field for accelerating the ions in the space between the front grid electrode and the rear grid electrode, when the ions are passing through the shutter gate grid.

2. The ion mobility spectrometer as set forth in claim 1, wherein: the gate grid controlling portion includes a circuit for generating pulse voltages to be applied respectively to the front grid electrode and the rear grid electrode, and the structure may be one wherein the difference in voltages, when applying a voltage to the front grid electrode that is higher than that of the rear grid electrode, can be adjusted through adjusting an offset voltage of the pulse voltage that is applied to the front grid electrode and/or the pulse voltage that is applied to the rear grid electrode.

3. The ion mobility spectrometer as set forth in claim 2, wherein: the controlling portion includes: a first amplifying portion for inputting a pulse signal and for amplifying the pulse signal and supplying the amplified pulse signal to the front grid electrode; a second amplifying portion for inputting the pulse signal and for amplifying the pulse signal and supplying the amplified pulse signal to the rear grid electrode; a pulse signal generating portion for generating a standard pulse signal; and a polarity switching portion for either maintaining as-is, or inverting, depending on an instruction from the outside, the polarity of the standard pulse signal generated by the pulse signal generating portion and then supplying standard pulse signal to the first and second amplifying portions.

4. The ion mobility spectrometer as set forth in claim 3, wherein: the first amplifying portion and the second amplifying portion each have offset electropotential adjusting portions.

5. A method of controlling an ion mobility spectrometer, having an ionizing portion for generating sample component derivative ions, and a drift region in order to cause ions, generated by the ionizing portion, to move in order to separate the depending on mobility and a shutter gate grid comprising a front grid electrode and a rear grid electrode disposed with a prescribed distance of separation in the direction of movement of the ions, between the ionizing portion and the drift region, in order to cut off or feed the ions into the drift region with short pulses; the method comprising: applying, to the rear grid electrode, a voltage that is higher than that of the front grid electrode, so as to form an electropotential barrier to the ions in the space between the front grid electrode and the rear grid electrode when cutting off the ions with the shutter grid gate, and applying, to the front grid electrode, a voltage that is higher than that of the rear grid electrode, so as to form an electric field for accelerating the ions in the space between the front grid electrode and the rear grid electrode, when the ions are passing through the shutter gate grid.

6. The method of controlling the ion mobility spectrometer as set forth in claim 5, further comprising generating pulse voltages to be applied respectively to the front grid electrode and the rear grid electrode, and the structure may be one wherein the difference in voltages, when applying a voltage to the front grid electrode that is higher than that of the rear grid electrode, can be adjusted through adjusting an offset voltage of the pulse voltage that is applied to the front grid electrode and/or the pulse voltage that is applied to the rear grid electrode.

7. The method of controlling the mobility spectrometer as set forth in claim 6, further comprising inputting a pulse signal and amplifying the pulse signal and supplying the amplified pulse signal to the front grid electrode by a first amplifying portion; inputting the pulse signal and amplifying the pulse signal and supplying the amplified pulse signal to the rear grid electrode by a second amplifying portion; generating a standard pulse signal by a pulse signal generating portion; either maintaining as-is, or inverting, depending on an instruction from the outside, the polarity of the standard pulse signal generated by the pulse signal generating portion and then supplying standard pulse signal to the first and second amplifying portions, by a polarity switching portion.

8. The method of controlling the mobility spectrometer as set forth in claim 7, wherein: the first amplifying portion and the second amplifying portion each have offset electropotential adjusting portions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a schematic structural diagram of an ion mobility spectrometer according to an embodiment according to the present invention.

[0026] FIG. 2 is a circuit structural diagram of a gate grid controlling portion in an ion mobility spectrometer according to this embodiment.

[0027] FIG. 3 is a diagram illustrating the result of simulation of a voltage waveform when the offset voltage in the circuit illustrated in FIG. 2 has been adjusted.

[0028] FIG. 4 is a comparison of the voltage waveforms applied to the grid electrodes in the ion mobility spectrometer according to this embodiment and in a conventional ion mobility spectrometer, and a schematic diagram of the electropotential gradient on the ion optical axis when the shutter gate grid is open.

[0029] FIG. 5 is a schematic structural diagram of a typical ion mobility spectrometer.

[0030] FIG. 6 is a schematic drawing wherein the grid electrodes in FIG. 5 are viewed from the direction in which the ions are introduced.

[0031] FIG. 7 is a schematic diagram of the voltage waveforms applied to the grid electrodes in the conventional ion mobility spectrometer, and of the electropotential gradient on the ion optical axis.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0032] An embodiment of an ion mobility spectrometer according to the present invention will be explained in reference to the appended drawings.

[0033] FIG. 1 is a schematic structural diagram of an ion mobility spectrometer that is one embodiment according to the present invention, and FIG. 2 is a circuit structural diagram of a gate grid controlling portion in the ion mobility spectrometer of this embodiment.

[0034] The basic structure of the ion mobility spectrometer in this embodiment is identical to that illustrated in FIG. 5. That is, the ion mobility spectrometer in the present embodiment has an ionizing region 10 and a drift region 11, and is provided with a shutter gate grid 12 at the boundary between the ionizing region 10 and the drift region 11. A plurality of ring-shaped electrodes 13 is disposed along the ion optical axis C in the ionizing region 10 and the drift region 11, where voltages obtained through voltage division, through a ladder resistance 15, of a prescribed DC voltage +HV, generated by a power supplying portion 16, are applied to the individual electrodes 13, to thereby form an electric field in the ionizing region 10 and the drift region 11.

[0035] The primary distinctive feature of the ion mobility spectrometer according to the present embodiment is in the circuit structure of the gate grid controlling portion 17 that applies the respective voltages to the pair of grid electrodes 12a and 12b. This circuit structure will be explained using FIG. 2.

[0036] A pulse signal that is generated in a pulse generating portion 170 passes through a resistance R1 and is supplied selectively, by a first switch 171, to an input terminal of a first photocoupler 172 or a second photocoupler 173. Both photocouplers 172 and 173 have Schmitt trigger built-in photodetectors, for waveform shaping, provided therein, wherein the first photocoupler 172 is of the inverted output type and the second photocoupler 173 is of the non-inverted appetite. Consequently, even though the pulse signals that are inputted into both photocouplers 172 and 173 are identical, the logic (that is, the “H” or “L” or the “1” or “0”) of the pulse signals that appear on the outputs of the two photocouplers 172 and 173 are mutually opposite.

[0037] The outputs of the two photocouplers 172 and 173 are selected by a second switch 174, and are inputted into both a non-inverting amplifying portion 175 and an inverting amplifying portion 177. The non-inverting amplifying portion 175 is structured including an op-amp OP1, resistances R2, R3, and R4, and a capacitor C1, and the inputted pulse signal is amplified under a prescribed amplification ratio. On the other hand, the inverting amplifying portion 177 is structured from an op-amp OP2, resistances R7 and R8, and a capacitor C2, and amplified under a prescribed application ratio after inverting the inputted pulse signal logic. The output of the non-inverting amplifying portion 175 is supplied to the front grid electrode 12a, and the output of the inverting amplifying portion 177 is supplied to the rear grid electrode 12b. Moreover, the non-inverting amplifying portion 175 is provided with an offset voltage adjusting portion 176 that includes resistances R5 and R6 and a variable resistance VR1, and, similarly, the inverting amplifying portion 177 is provided with an offset voltage adjusting portion 178 including resistances R9 and R10 and a variable resistance VR2.

[0038] In FIG. 2, +Vr is a positive power supply voltage, −Vr is a negative power supply voltage, and Vref is a reference voltage. The input side and the output side are insulated electrically by photocouplers 172 and 173, where the input sides of the photocouplers 172 and 173 use GND (ground) as the reference electropotential, while, in contrast, the output sides of the photocouplers 172 and 173 use the reference voltage Vref as the reference electropotential.

[0039] Based on a control signal supplied to the pulse generating portion 170 from the controlling portion 18, the pulse generating portion 170 generates pulse signals of a prescribed width with a prescribed period. In this case, the pulse width is the time over which the shutter gate grid 12 will be open, and thus, by adjusting the pulse width, it is possible to adjust the time over which the shutter gate grid 12 is open. The first switch 171 and second switch 174 are switched in coordination through the polarity switching signal Pol that is supplied from the controlling portion 18. For example, if the ions that are subject to analysis are positive ions, then, through the polarity switching signal Pol, both the first and second switches 171 and 174 are switched to the top side as shown in FIG. 2, that is, they select the first photocoupler 172. In this case, the pulse signal that is outputted from the pulse generating portion 170 has the logic thereof inverted as it passes through the first photocoupler 172, and then is inputted into the non-inverting amplifying portion 175 and the inverting amplifying portion 177.

[0040] The pulse signal that is inputted into the non-inverting amplifying portion 175 has the amplitude amplified, with the logic thereof inverted, and the electropotential that is applied to the inverting input terminal of the op-amp OP1 is the reference electropotential for this amplification. Because of this, when the electropotential that is applied to the inverting input terminal of the op-amp OP1 is changed through an adjustment to the variable resistance VR1, the offset of the pulse voltage of the output of the non-inverting amplifying portion 175 changes, to shift the signal waveform in the direction of the voltage axis while the amplitude thereof is maintained as-is. On the other hand, the pulse signal that is inputted into the inverted amplifying portion 177 has the amplitude amplified with the logic remaining as-is, and the electropotential that is applied to the non-inverting input terminal of the op-amp OP2 is the reference electropotential for this amplification. Because of this, when the electropotential that is applied to the non-inverting input terminal of the op-amp OP2 is changed through an adjustment to the variable resistance VR2, the offset of the pulse voltage that is the output of the inverted amplifying portion 177 changes, to shift the signal waveform in the direction of the voltage axis while the amplitude thereof is maintained as-is.

[0041] FIG. 3 is a diagram illustrating the result of a simulation of the voltage waveform when the offset voltage in the circuit illustrated in FIG. 2 is adjusted. As shown in FIG. 3, the offset voltage of the pulse voltage that is applied to the grid electrode 12a (or 12b) can be adjusted through changing the resistance value of the variable resistance VR1 (or VR2).

[0042] FIG. 4 is a comparison of the voltage waveforms applied to the grid electrodes 12a and 12b in the ion mobility spectrometer in the present embodiment and in the conventional ion mobility spectrometer, and schematic diagrams of the electropotential gradients on the ion optical axis when the shutter gate grid is open. As described above, in the conventional ion mobility spectrometer, the grid electrodes 12a and 12b are at identical electropotentials when the shutter gate grid 12 is open. As illustrated in FIG. 4 (a), this is the state wherein the offset voltage in the gate grid controlling portion 17 in the ion mobility spectrometer according to the present embodiment is 0, where the voltage value corresponding to the logic “H” of the pulse voltage that is applied to the front grid electrode 12a matches the voltage value corresponding to the logic “L” of the pulse voltage that is applied to the rear grid electrode 12b.

[0043] In contrast, in the ion mobility spectrometer according to the present embodiment, the variable resistance VR1 in the offset adjusting portion 176, as described above, and the variable resistance VR2 in the offset voltage adjusting portion 178, are adjusted to shift, in the direction of the voltage axis, the pulse voltages that are applied to the grid electrodes 12a and 12b. Consequently, the variable resistances VR1 and VR2 can be adjusted as appropriate to cause the voltage value corresponding to the logic “H” of the pulse voltage that is applied to the front grid electrode 12a to be higher, by a prescribed voltage, than the voltage value corresponding to the “L” logic of the pulse voltage that is applied to the rear grid electrode 12b, as illustrated in FIG. 4 (b). In this case, the electropotential gradient along the ion optical axis will gradually slope declining from the front grid electrode 12a toward the rear grid electrode 12b, as illustrated on the right in FIG. 4 (b), to form an electric field that accelerates ions in the space between the front grid electrode 12a and the rear grid electrode 12b.

[0044] When the shutter gate grid 12 is opened from a state wherein the shutter gate grid 12 was closed and an electropotential barrier was formed in the vicinity of the shutter gate grid 12, as illustrated in FIG. 7 (c), and an accelerating electric field is formed in the vicinity of the shutter gate grid 12, as illustrated in FIG. 4 (b), then this accelerates the movement of the ions that have accumulated to the front of the electropotential barrier, to quickly pass through the shutter gate grid 12, to be introduced into the drift region 11. This causes the pulse width of the ions to be narrower when the ions pass through the shutter gate grid 12, thereby improving the temporal resolution of the spectrum.

[0045] However, if the electropotential gradient in the space between the front grid electrode 12a and the rear grid electrode 12b is too large, then the kinetic energy that is applied to the ions when passing through here will be too large, and the performance in separating the ions in accordance with the mobility in the drift region 11 will suffer. Of course, if the electropotential gradient in the space between the front grid electrode 12a and the rear grid electrode 12b is too small, then the effect of narrowing the pulse width of the ions in the shutter gate grid 12 will be inadequate. Given this, the potential difference between the grid electrodes 12a and 12b when the shutter gate grid 12 is open should be adjusted as appropriate in advance by the analyzing technician, or the like, through adjusting the variable resistance VR1 of the offset voltage adjusting portion 176 and the variable resistance VR2 in the offset voltage adjusting portion 178.

[0046] Specifically, the analyzing technician should adjust the variable resistances VR1 and VR2 so as to minimize the time band of the spectrum relative to ions derived from the target component while observing the ion detection signal obtained by the ion detector 14 by carrying out an analysis of a sample that includes a known component, such as, for example, a reference sample. This makes it possible to produce a state wherein the potential difference between the pair of grid electrodes 12a and 12b when the shutter gate grid 12 is open will be optimal or nearly optimal.

[0047] Note that, as is clear from FIG. 4 (b), if an offset voltage is applied so as to produce the potential difference between the pair of grid electrodes 12a and 12b when the shutter gate grid 12 is open, then the potential difference will be smaller when the shutter gate grid 12 is closed, reducing the electropotential barrier. However, this is no problem whatsoever in practice because the potential difference for forming the electropotential barrier to begin with is adequately large when compared to the potential difference that is produced by the offset voltage. Moreover, as necessary, the structure may be one wherein the amplitude of the pulse voltage can be increased, through making it possible to adjust the non-inverting amplifying portion 175 and the inverting amplifying portion 177.

[0048] If the ions that are subject to analysis are negative ions, then the first and second switches 171 and 174 are both switched to the bottom side in FIG. 2, by the polarity switching signal Pol that is supplied from the controlling portion 18, to select the second photocoupler 173. In this case, the pulse signal that is outputted from the pulse generating portion 170 will pass through the second photocoupler 173 with the logic thereof preserved, to be inputted into the non-inverting amplifying portion 175 and the inverting amplifying portion 177. That is, when analyzing positive ions, a pulse signal wherein the positive/negative logic has been inverted is inputted into the non-inverting amplifying portion 175 and the inverting amplifying portion 177. Because both the non-inverting amplifying portion 175 and the inverting amplifying portion 177 have the reference voltage Vref as the reference point for the amplification operation, when analyzing positive ions, as described above, a pulse voltage is generated wherein the positive and negative are inverted, centered on this reference voltage Vref. Consequently, in this case as well, an electric field wherein the ions (in this case, negative ions) are accelerated is produced in the space between the front grid electrode 12a and the rear grid electrode 12b, and, as a result, the pulse width of the ions when the ions pass through the shutter gate grid 12 will be narrowed. Moreover, in this case, the potential difference between the front grid electrode 12a and the rear grid electrode 12b will be the same as for the positive ion analysis, and thus there is no need to readjust the offset voltage using the variable resistances VR1 and VR2.

[0049] Note that, as described above, because the pulse width of the pulse signal that is generated by the pulse generating portion 170 is the time over which the shutter gate grid 12 is open, the time over which the shutter gate grid 12 is open can be adjusted through changing this pulse width. Moreover, for the amplitude of the pulse voltage that is applied to the grid electrodes 12a and 12b, the amplification ratios of the non-inverted amplifying portion 175 and of the inverted amplifying portion 177 may be adjusted (through, for example, adjusting the values of feedback resistances R3 and R8).

[0050] Note that the embodiment described above is no more than an example of the present invention, where, of course, even if there are arbitrary changes, corrections, or additions within a scope that does not deviate from the spirit or intent of the present invention, these are, of course, included within the patent claims of the present invention.

[0051] For example, the structure of the ionizing region in the ion mobility spectrometer of the embodiment set forth above may be changed arbitrarily, where, for example, an ion source through any of a variety of ionization techniques such as used in, for example, mass spectrometers may be substituted. Moreover, rather than measuring the mobility of the ionized sample molecules, product ions that are broken down through, for example, a collision-induced dissociation or optically-induced dissociation may be introduced into the drift region, to measure the mobility thereof.

[0052] Moreover, the present invention may also be applied to an ion mobility spectrometer-mass spectrometer wherein the ions that have been separated in accordance with the mobility thereof in the drift region are introduced into a quadrupole mass filter, or the like, to be separated further in accordance with the mass/electric charge ratio and then subjected to detection.

Explanations of Reference Symbols

[0053] 10: Ionizing Region [0054] 11: Drift Region [0055] 12: Shutter Gate Grid [0056] 12a: Front Grid Electrode [0057] 12b: Rear Grid Electrode [0058] 13: Ring-shaped Electrode [0059] 14: Ion Detector [0060] 15: Ladder Resistance [0061] 16: Power Supplying Portion [0062] 17: Gate Grid Controlling Portion [0063] 170: Pulse Generating Portion [0064] 171, 174: Switches [0065] 172, 173: Photocouplers [0066] 175: Non-Inverting Amplifying Portion [0067] 177: Inverting Amplifying Portion [0068] 176, 178: Offset Voltage Adjusting Portions [0069] R1 through R10: Resistances [0070] VR1, VR2: Variable Resistances [0071] C1, C2: Capacitors [0072] OP1, OP2: Op-amps [0073] 18: Controlling Portion