JP6972519B2 - Ion detector - Google Patents

Description

The present invention relates to an ion detection device, and more particularly to an ion detection device that selects and detects ions.

As one of the methods for analyzing a gas or a vaporized chemical substance, there is a method called field asymmetric waveform ion mobility spectroscopy (hereinafter also referred to as "FAIMS") (for example, Patent Document 1). See ~ 3).

In this method, ionized gas molecules and chemical substances (hereinafter collectively referred to as "chemical substances") are passed through an ion filter, sorted according to the difference in mobility, and detected by a detector. The chemical substance or the like is specified by the above method.

In recent years, the analyzer used for FAIMS (hereinafter, also referred to as "ion detector") has been required to be miniaturized and portable so that it can be analyzed at various sites.

However, in the conventional ion detection device, the device is large and difficult to carry.

The present invention comprises an ion generator that ionizes the molecule to be measured, an ion filter that selects ions ionized by the ion generator, a detector that detects ions selected by the ion filter, and the detector. It is an ion detection device provided with an air flow generator which is arranged in a subsequent stage and can generate an ion wind by corona discharge.

According to the ion detection device of the present invention, the device can be easily carried due to the miniaturization of the device.

It is a schematic block diagram of the ion detection apparatus which concerns on one Embodiment. It is a figure for demonstrating the electric field strength dependence of the ion mobility. It is a figure (the 1) for demonstrating the locus of movement of three ions (ion A, ion B, ion C) between the electrodes of an ion filter part. It is a figure for demonstrating the electric field waveform generated between the electrode A and the electrode B. It is a figure (the 2) for demonstrating the locus of movement of three ions (ion A, ion B, ion C) between the electrodes of an ion filter part. It is a figure for demonstrating the ion detection apparatus of Example 1. FIG. It is an enlarged view of a part of an airflow generator. It is a figure for demonstrating the generation of an ionic wind by a corona discharge. It is a figure (the 1) for demonstrating the generation of an ionic wind in an airflow generator. It is a figure (the 2) for demonstrating the generation of an ionic wind in an airflow generator. It is a figure for demonstrating the ion detection apparatus of Example 2. It is a figure for demonstrating the ion detection apparatus of Example 3. FIG. It is a figure for demonstrating the ion detection apparatus of Example 4.

"Overview"
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an ion detection device 10 according to an embodiment.

The ion detection device 10 includes an ion generation unit 100, an ion filter unit 200, a detection unit 600, a control unit 900, and the like. Here, the XYZ three-dimensional Cartesian coordinate system is used, and the traveling direction of the molecule to be measured is the + Z direction.

The ion generation unit 100 ionizes the molecule to be measured. The ion filter unit 200 selects ions from the ion generation unit 100. The detection unit 600 detects the ions selected by the ion filter unit 200. The control unit 900 controls the entire device.

The basic detection principle of the ion detection device 10 will be described.

The ion filter unit 200 has two electrodes (electrode A and electrode B) arranged so as to face each other.

The ions move at the moving speed V represented by the following equation (1) in the environment of the electric field E. Here, K is the mobility of the ion.
V = K × E …… (1)

By the way, the mobility of ions depends on the electric field strength. And this electric field strength dependence differs depending on the type of ion. FIG. 2 shows, as an example, the electric field strength dependence of the mobility of three different types of ions (ion A, ion B, and ion C). In FIG. 2, the mobility of each ion is normalized so as to be equal at an electric field strength of 0 for the sake of clarity.

The mobilities of the three ions (ion A, ion B, and ion C) are almost unchanged at low electric field strengths of 9 kV / cm or less. As the electric field strength increases from about 10 kV / cm, the ion type-specific characteristics appear in the mobility. The mobility of ion A increases greatly as the electric field strength increases, and becomes maximum at Emax. The mobility of ion B increases more slowly than that of ion A. The mobility of ion C gradually decreases. In this way, the characteristics of the three parties are shown. The ion filter unit 200 selects ions by utilizing the difference between the mobility at low electric field strength and the mobility at high electric field strength.

FIG. 3 shows the locus of movement of three ions (ion A, ion B, and ion C) between the electrodes of the ion filter unit 200. Here, for the sake of clarity, the electrodes A and B are made of parallel flat plates made of a conductor for convenience.

By making the waveform of the electric field generated between the electrode A and the electrode B an asymmetric electric field waveform, only arbitrary ions (ion B in FIG. 3) can reach the detection unit 600.

FIG. 4 shows an example of an electric field waveform generated between the electrode A and the electrode B. This electric field waveform alternately repeats a positive high electric field (Emax) and a negative low electric field (Emin). The period of high electric field (t1) is shorter than the period of low electric field (t2), and the ratio of t1 to t2 is 1: 3 to 1: 5. Thus, the electric field waveform is asymmetric with respect to the top and bottom. This asymmetric electric field waveform has a time average electric field of zero, and is set so that the following equation (2) holds.
| Emax | × t1 = | Emin | × t2 …… (2)

That is, the area of the area A and the area of the area B in FIG. 4 are set to match.

In the following, as shown in the following equation (3), the value of | Emax | × t1 and the value of | Emin | × t2 are defined as β.
| Emax | × t1 = | Emin | × t2 = β …… (3)

By the way, the velocity Vup in which the ions move in the Y-axis direction during the period of high electric field (t1) is expressed by the following equation (4). Here, K (Emax) is the mobility of ions at the time of high electric field (Emax).
Vup = K (Emax) × | Emax | …… (4)

For example, when | Emax | is about 10 kV / cm or more, the mobility of the three ions (ion A, ion B, ion C) is different for each ion (see FIG. 2), so that the mobility of the three ions is Vup. Is different in three ways. That is, as shown in FIG. 5, in the period of high electric field (t1), the slopes of the movement loci of the three ions are different from each other.

The displacement up (see FIG. 5), which is the distance the ions have traveled in the Y-axis direction during the period of high electric field (t1), is expressed by the following equation (5).
yup = Vup × t1 …… (5)

On the other hand, the velocity Vdown in which the ions move in the Y-axis direction during the period of low electric field (t2) is expressed by the following equation (6). Here, K (Emin) is the mobility of the ion at the time of low electric field (Emin).
Vdown = -K (Emin) × | Emin | …… (6)

For example, when | Emin | is about 5 kV / cm or less, the mobilities of the three ions (ion A, ion B, and ion C) are almost the same (see FIG. 2), so that the mobility of the three ions is Vdown. Are almost the same. That is, as shown in FIG. 5, the slopes of the movement loci of the three ions are almost the same during the low electric field period (t2).

The displacement ydown (see FIG. 5), which is the distance the ions have traveled in the Y-axis direction during the low electric field period (t2), is expressed by the following equation (7).
ydown = Vdown × t2 …… (7)

Within one cycle (T) of the asymmetric electric field waveform, the ions move in the + Z direction, move in the + Y direction during the period t1, and move in the −Y direction during the period t2.

Therefore, as shown in FIG. 5, the one toward the electrode A while repeating the zigzag motion (ion A), the one toward the electrode B while repeating the zigzag motion (ion C), and the displacement in the + Y direction and the −Y direction. Is balanced with the displacement of, and is separated into the one toward the detection unit (ion B).

By the way, the average displacement ΔyRF of the ions in the Y-axis direction in one cycle (T) in the asymmetric electric field waveform is expressed by the following equation (8).
ΔyRF = up + ydown
= K (Emax) × | Emax | × t1-K (Emin) × | Emin | × t2 …… (8)

Then, the above equation (8) can be expressed as the following equation (9) by using the above equation (3).
ΔyRF = β {K (Emax) -K (min)} …… (9)

Here, assuming that K (Emax) −K (min) is ΔK, the above equation (9) is expressed as the following equation (10).
ΔyRF = βΔK …… (10)

β is a constant determined by the asymmetric electric field applied between the electrode A and the electrode B. Therefore, the displacement of the ion in the Y-axis direction per period (T) of the asymmetric electric field waveform depends on ΔK, which is the difference between the mobility in the low electric field (Emin) and the mobility in the high electric field (Emax).

Assuming that only the carrier gas transfers the ions in the Z-axis direction, the displacement Y of the ions with respect to the Y-axis direction when the ions stay between the electrode A and the electrode B is as follows (11). It becomes an expression. Here, tres is the average time (average ion stay time) in which ions stay between the electrode A and the electrode B.

The average ion stay time tres is expressed by the following equation (12). Here, A is the cross-sectional area of the ion filter portion, L is the length of the electrode in the Z-axis direction (electrode depth) (see FIG. 5), and Q is the volumetric flow rate of the carrier gas. V is the volume (= AL) of the ion filter unit.

The above equation (11) can be expressed as the following equation (13) by using the above equation (12) and the above equation (3). Here, D is the duty of the asymmetric electric field waveform, and D = t1 / T.

When the same values are used for the high electric field Emax in the asymmetric electric field waveform, the volume V of the ion filter unit, the duty D of the asymmetric electric field waveform, and the volumetric flow rate Q of the carrier gas, the above equation (13) is used. From this, it can be seen that the displacement Y is proportional to the difference ΔK between the mobility in the low electric field (Emin) and the mobility in the high electric field (Emax) peculiar to the ion species.

In FIG. 5, only the ion B has the minimum displacement Y and can reach the detection unit 600, but by changing the duty D, an ion having a ΔK different from that of the ion B reaches the detection unit 600. Can be made to. Further, by changing the duty D in small steps, it is possible to detect the presence / absence and amount of various ions having different ΔK.

Further, as a method of detecting various ion species having different ΔK in the ion detection device 10, there is a method of superimposing a low-intensity DC electric field on the asymmetric electric field waveform. According to this method, the displacement amount in the Y-axis direction in the period t1 and the period t2 can be changed. Therefore, the ion species that can reach the detection unit 600 without contacting the electrode A or the electrode B can be continuously changed. The DC electric field superimposed on the asymmetric electric field waveform is called a compensation voltage (CV). In this method, the compensation voltage is swept to detect the presence or absence and amount of various ion species having different ΔK.

By the way, the ions that come into contact with the electrode A or the electrode B before reaching the detection unit 600 are neutralized and become non-ions and are not detected.

Since the control unit 900 is almost the same as the control unit in the conventional ion detection device, detailed description of the operation of the control unit 900 will be omitted here.

"detail"
The ion detection device is a device that detects the type and amount of a trace amount of molecules contained in a gas. The ion detector is highly versatile and is widely used for analysis of drugs and chemical components in samples, analysis of harmful gases in the environment, biogas, and odors, but the device is relatively large and used. The environment is limited.

In addition, conventional ion detection devices require pumps and the like, and none of them are highly portable. Further, in Patent Document 3, the size is reduced by utilizing the gradient potential and eliminating the need for flow gas, but it is portable because the control circuit is complicated and the ion generating means uses a radioactive isotope. Was unsuitable for.

<Example 1>
The ion detection device 10 of the first embodiment is shown in FIG. In the ion detection device 10, the detection unit 600 has a detector 610 and an air flow generator 620. The airflow generator 620 is arranged on the + Z side of the detector 610.

An enlarged view of a part of the airflow generator 620 is shown in FIG. The airflow generator 620 has a plurality of three types of electrodes (electrode 1, electrode 2, electrode 3), respectively. The electrode 1 has a sharp end (tip) in the + Z direction. The electrode 1 is sandwiched between the two electrodes 2 in a direction orthogonal to the Z-axis direction (Y-axis direction in FIG. 7). The electrode 3 is arranged on the + Z side of the electrode 2. The electrode 3 is insulatingly coated. Further, the airflow generator 620 has a single power supply 621 connected to each electrode.

FIG. 8 is a diagram for explaining a basic airflow generation mechanism due to corona discharge. By increasing the voltage between the electrode 1 and the electrode 3, the electric field spreads around the tip of the electrode 1, an electric line of force is generated as shown in FIG. 8, and the electric field strength near the tip of the electrode 1 is increased. When it exceeds about 4 × 10 ⁷ Vm, ions are generated from the vicinity of the tip of the electrode 1, and the generated ions move according to the lines of electric force, so that an air flow is generated as if the ion gas pushes out the surrounding gas. This airflow is called ionic wind or simply wind.

In the airflow generator 620, ions are generated by the corona discharge, and the ions move along the lines of electric force due to the repulsion between the + ions and the electric and electric lines of force of the electrodes 1 and 2. Then, due to the movement of the ions, the surrounding gas also moves so as to be pushed, and an air flow is generated (see FIGS. 9 and 10).

In this case, the ion wind can be safely generated. In addition, the generation of ions and the generation of wind can be realized simultaneously with a single power supply 621. As a result, it is possible to realize a small, safe and easy-to-control ion detection device suitable for carrying.

Here, in order to prevent the flow of ions from flowing back to the detector 610, the airflow generator 620 has the polarity of the generated ions opposite to that of the ion generating unit 100, and the position is not so affected by the electric field. It is provided in.

Further, in the present embodiment, the case where the airflow generator 620 is configured as a part of the detection unit 600 has been described, but the present invention is not limited to this, and the airflow generator 620 has the function of the detection unit 600. It may be configured in isolation. Further, in this embodiment, the case where the airflow generator 620 is provided after the detector 610 has been described, but the present invention is not limited to this, and any configuration can realize the effects of the present embodiment. The installation position of the airflow generator 620 does not matter.

<Example 2>
The ion detection device 10 of the second embodiment is shown in FIG. The ion detection device 10 is characterized in that the voltage applied to the airflow generator 620 is variable with respect to the ion detection device 10 of the first embodiment. In this case, the same effect as that of the ion detection device 10 of the first embodiment can be obtained, and the flow rate of the ion wind can be changed.

<Example 3>
The ion detection device 10 of Example 3 is shown in FIG. The ion detection device 10 is characterized in that the airflow generator 620 also serves as the ion generation unit 100 with respect to the ion detection device 10 of the first embodiment.

In the ion detection device 10 of the third embodiment, the airflow generator 620 is arranged on the −Z side of the ion filter unit 200.

In this case, the same effect as that of the ion detection device 10 of the first embodiment can be obtained, and the size can be further reduced.

By the way, the amount of ion detected can be adjusted by adjusting the number of electrodes constituting the ion generating unit 100 and the airflow generator 620 or the applied voltage. Further, even when the polarity applied to the ion generating unit 100 is changed, the airflow generator 620 can generate an ion wind in the same direction regardless of whether it is a positive ion or a negative ion.

<Example 4>
The ion detection device 10 of the fourth embodiment is shown in FIG. The ion detection device 10 is characterized in that the distance between the ion generation unit 100 and the ion filter unit 200 in the Z-axis direction is longer than that of the ion detection device 10 of the first embodiment.

When there are many ions of nitrogen and oxygen contained in the ions generated by the ion generation unit 100 and there is a possibility that it takes time for other molecules to be ionized, as in the ion detection device 10 of Example 4. It is preferable to increase the distance between the ion generating unit 100 and the ion filter unit 200 to save time and ensure that other molecules are ionized. In this case as well, the same effect as that of the ion detection device 10 of the first embodiment can be obtained.

As described above, the ion detection device 10 according to the present embodiment includes an ion generation unit 100, an ion filter unit 200, a detection unit 600, a control unit 900, and the like.

The detection unit 600 has an airflow generator 620 capable of generating ionized wind by corona discharge. The airflow generator 620 has a plurality of three types of electrodes (electrode 1, electrode 2, electrode 3), respectively. The airflow generator 620 also has a flow path penetrating in the + Z direction.

The ion detection device 10 can safely generate ion wind, and can simultaneously generate ions and wind with a single power source. As a result, it is possible to realize a small, safe and easy-to-control ion detection device suitable for carrying.

Further, in the ion detection device 10 of the second embodiment, the voltage at the time of corona discharge in the airflow generator 620 is variable.

Further, in the ion detection device 10 of the third embodiment, the airflow generator 620 also serves as the ion generation unit 100.

Further, in the ion detection device 10 of the fourth embodiment, a space for promoting ionization of the molecule to be measured is provided between the ion generation unit 100 and the ion filter unit 200.

In the above embodiment, the case where the ion generating unit 100 has a plurality of electrodes has been described, but the present invention is not limited to this, and the ion generating unit 100 may have one electrode.

10 ... ion detector, 100 ... ion generator (ion generator), 200 ... ion filter unit (ion filter), 600 ... detector, 610 ... detector, 620 ... airflow generator, 621 ... single power supply, 900 … Control unit.

U.S. Patent Application Publication No. 2015/0028196 Japanese Patent No. 4063676 Japanese Patent No. 5221954

Claims (7)

An ion generator that ionizes the molecule under test and
An ion filter that selects ions ionized by the ion generator, and
A detector that detects the ions selected by the ion filter, and
An airflow generator that is placed after the detector and can generate ionic wind by corona discharge.
Ion detector with. The ion detection device according to claim 1, wherein the air flow generator has two or more electrodes and a penetrating flow path. The ion detection device according to claim 1 or 2, wherein the airflow generator has a variable voltage during corona discharge. The ion detection device according to any one of claims 1 to 3, wherein the voltage applied to the airflow generator and the voltage applied to the ion generator are individually controlled. The ion detection device according to any one of claims 1 to 4, wherein the airflow generator has a single power source for generating ions and generating wind. The ion detection device according to any one of claims 1 to 5, wherein a space for promoting ionization of the molecule to be measured is provided between the ion generator and the ion filter. The ion detection device according to any one of claims 1 to 6, wherein the ion generator has one or more electrodes.

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