JP2018021859A - Ion detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion detector which can be easily carried by a user.SOLUTION: An ion detector 10 includes an ion generation unit 100, an ion filter unit 200, a detection unit 600, and a control unit. The detection unit 600 has a detector 610 and an air flow generator 620. The air flow generator 620 can generate ion wind by corona discharge. In that case, the ion detector 10 can generate ion wind safely and can realize ion generation and wind generation at one time with one power source. It thus becomes possible to realize an ion detector which is small and safe, is easily controlled, and is suitable for carrying.SELECTED DRAWING: Figure 6

Description

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

  One method for analyzing gas and vaporized chemical substances is a method called Field Asymmetric Waveform Ion Mobility Spectroscopy (hereinafter also referred to as “FAIMS”) (for example, Patent Document 1). To 3).

  In this method, ionized gas molecules and chemical substances (hereinafter collectively referred to as “chemical substances”) are screened by an ion filter based on the difference in mobility and detected by a detector. The chemical substance or the like is specified by

  In recent years, analyzers used in FAIMS (hereinafter also referred to as “ion detectors”) have been required to be small and portable so that they can be analyzed at various sites.

  However, in the conventional ion detector, the apparatus is large and difficult to carry.

  The present invention includes an ion generator that ionizes a 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 ion generator And an airflow generator for generating a flow for transferring ions ionized by the ion filter toward the ion filter by corona discharge.

  According to the ion detector of the present invention, it can be easily carried by downsizing the device.

It is a schematic block diagram of the ion detector which concerns on one Embodiment. It is a figure for demonstrating the electric field strength dependence of the mobility of ion. It is FIG. (1) for demonstrating the locus | trajectory of a movement of three ion (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. FIG. It is FIG. (2) for demonstrating the movement locus | trajectory of three ion (ion A, ion B, ion C) between the electrodes of an ion filter part. It is a figure for demonstrating the ion detector of Example 1. FIG. It is the figure which expanded a part of airflow generator. It is a figure for demonstrating the production | generation of the ion wind by a corona discharge. It is FIG. (1) for demonstrating the production | generation of the ion wind in an airflow generator. It is FIG. (2) for demonstrating the production | generation of the ion wind in an airflow generator. It is a figure for demonstrating the ion detector of Example 2. FIG. It is a figure for demonstrating the ion detector of Example 3. FIG. It is a figure for demonstrating the ion detector of Example 4. FIG.

"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 detector 10 according to an embodiment.

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

  The ion generator 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 ions selected by the ion filter unit 200. The control unit 900 controls the entire apparatus.

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

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

In the environment of the electric field E, the ions move at a moving speed V expressed by the following equation (1). Here, K is the mobility of the ions.
V = K × E (1)

  By the way, ion mobility has electric field strength dependency. And this electric field strength dependence changes with kinds 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, for ease of understanding, the mobility of each ion is normalized so that the electric field strength is equal to zero.

  The mobility of the three ions (ion A, ion B, and ion C) is almost unchanged at a low electric field strength of 9 kV / cm or less. As the electric field strength increases from about 10 kV / cm, characteristics specific to the type of ion appear in the mobility. The mobility of ions A greatly increases as the electric field strength increases, and reaches a maximum at Emax. The mobility of ions B increases more slowly than ions A. The mobility of ions C gradually decreases. In this way, the characteristics of the tripartite are shown. The ion filter unit 200 performs ion selection using the difference between the mobility at a low electric field strength and the mobility at a high electric field strength.

  FIG. 3 shows a trajectory of movement of three ions (ion A, ion B, ion C) between the electrodes of the ion filter unit 200. Here, for the sake of simplicity, the electrodes A and B are parallel 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. In this electric field waveform, a positive high electric field (Emax) and a negative low electric field (Emin) are alternately repeated. The high electric field period (t1) is shorter than the low electric field period (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 upper and lower sides. This asymmetric electric field waveform is set such that the time-average electric field is zero and the following equation (2) is satisfied.
| Emax | × t1 = | Emin | × t2 (2)

  That is, the area of the region A and the area of the region B in FIG.

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

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

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

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

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

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

The displacement ydown (see FIG. 5), which is the distance that the ions have moved 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 period (T) of the asymmetric electric field waveform, ions move in the + Z direction while moving 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 head toward the electrode A while repeating the zigzag motion (ion A), the head toward the electrode B while repeating the zigzag motion (ion C), the displacement in the + Y direction, and the −Y direction. Is balanced with the displacement (ion B) toward the detection unit.

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

And said (8) Formula can be represented like the following (9) Formula using said (3) Formula.
ΔyRF = β {K (Emax) −K (min)} (9)

Here, when K (Emax) −K (min) is set to ΔK, the above equation (9) is expressed as the following equation (10).
ΔyRF = βΔK (10)

  β is a constant determined by an asymmetric electric field applied between the electrode A and the electrode B. Therefore, the displacement of the ions per cycle (T) of the asymmetric electric field waveform in the Y-axis direction 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 transports ions in the Z-axis direction, the displacement Y of the ions in the Y-axis direction when the ions stay between the electrodes A and B is the following (11) It becomes an expression. Here, tres is an average time during which ions stay between the electrode A and the electrode B (average ion stay time).

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

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

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

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

  In addition, as a method for detecting various ion species having different ΔK in the ion detector 10, there is a method of superimposing a low-intensity DC electric field on an asymmetric electric field waveform. According to this method, the amount of displacement in the Y-axis direction during 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 compensation voltage (CV: compensation voltage). In this method, the presence / absence and amount of various ion species having different ΔK are detected by sweeping the compensation voltage.

  By the way, the ions that have contacted the electrode A or the electrode B before reaching the detection unit 600 are neutralized and are not detected.

  In addition, since the control part 900 is substantially the same as the control part in the conventional ion detection apparatus, detailed description about operation | movement of the control part 900 is abbreviate | omitted here.

"Details"
An ion detector is a device that detects the type and amount of a trace amount of molecules contained in a gas. Ion detection devices are highly versatile and are used in a wide range of applications, including analysis of drugs and chemical components in samples, and analysis of harmful gases, biological gases, and odors in the environment. The environment is limited.

  In addition, a conventional ion detector requires a pump or the like, and no portable device has been found. Moreover, in Patent Document 3, the gradient potential is used to reduce the size by eliminating the flow gas. However, since the control circuit is complicated and the ion generating means uses a radioisotope, it is portable. It was unsuitable to do.

<Example 1>
An ion detection apparatus 10 of Example 1 is shown in FIG. In the ion detection apparatus 10, the detection unit 600 includes a detector 610 and an airflow generator 620. The airflow generator 620 is disposed on the + Z side of the detector 610.

  A magnified view of a portion of the airflow generator 620 is shown in FIG. The airflow generator 620 includes a plurality of three types of electrodes (electrode 1, electrode 2, and electrode 3). The electrode 1 has a sharp end (tip) in the + Z direction. The electrode 1 is sandwiched between two electrodes 2 in a direction orthogonal to the Z-axis direction (Y-axis direction in FIG. 7). The electrode 3 is disposed on the + Z side of the electrode 2. The electrode 3 is insulated. In addition, the airflow generator 620 has a single power source 621 connected to each electrode.

FIG. 8 is a diagram for explaining a basic generation mechanism of airflow by corona discharge. By increasing the voltage between the electrode 1 and the electrode 3, an electric field spreads around the tip of the electrode 1, electric field lines are generated as shown in FIG. 8, and the electric field strength near the tip of the electrode 1 is increased. If 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 so that 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 corona discharge, and ions move along the lines of electric force due to repulsion between + ions and the electric field and electric lines of force of the electrodes 1 and 2. And by the movement of the ion, it moves so that the surrounding gas may also be pushed and an airflow will generate | occur | produce (refer FIG.9 and FIG.10).

  In this case, an ionic wind can be generated safely. In addition, the generation of ions and the generation of wind can be realized by the single power source 621 at the same time. As a result, a small, safe and easy-to-control ion detector suitable for carrying can be realized.

  Here, since the airflow generator 620 does not reverse the flow of ions to the detector 610, the polarity of ions to be generated is opposite to that of the ion generator 100, and the position where the influence of the electric field does not reach much. Is provided.

  In the present embodiment, the case where the airflow generator 620 is configured as a part of the detection unit 600 has been described. However, the present invention is not limited to this, and the airflow generator 620 includes the function of the detection unit 600. It may be configured separately. Furthermore, in the present embodiment, the case where the airflow generator 620 is provided in the subsequent stage of the detector 610 has been described. However, the present invention is not limited to this, and any configuration that can realize the effects of the present embodiment is provided. The installation position of the airflow generator 620 is not limited.

<Example 2>
An ion detector 10 of Example 2 is shown in FIG. The ion detector 10 is characterized in that the voltage applied to the airflow generator 620 is variable with respect to the ion detector 10 of the first embodiment. In this case, the same effect as the ion detector 10 of Example 1 can be obtained, and the flow rate of the ion wind can be changed.

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

  In the ion detector 10 of Example 3, the airflow generator 620 is disposed on the −Z side of the ion filter unit 200.

  In this case, the same effect as the ion detection apparatus 10 of Example 1 can be obtained, and further downsizing can be achieved.

  By the way, the ion detection amount can be adjusted by adjusting the number of electrodes constituting the ion generator 100 and the airflow generator 620 or the applied voltage. Further, even when the polarity applied to the ion generator 100 is changed, the airflow generator 620 can generate an ion wind in the same direction for both positive ions and negative ions.

<Example 4>
An ion detection apparatus 10 of Example 4 is shown in FIG. This 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 nitrogen and oxygen ions contained in the ions generated by the ion generator 100 and there is a possibility that it will take time for other molecules to be ionized, as in the ion detector 10 of the fourth embodiment. It is preferable to increase the distance between the ion generation unit 100 and the ion filter unit 200 to gain time and to ensure that other molecules are ionized. Also in this case, the same effect as the ion detector 10 of Example 1 is acquired.

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

  And the detection part 600 has the airflow generator 620 which can produce | generate an ion wind by corona discharge. The airflow generator 620 includes a plurality of three types of electrodes (electrode 1, electrode 2, and electrode 3). The air flow generator 620 also has a flow path that penetrates in the + Z direction.

  The ion detector 10 can safely generate ion wind and can simultaneously generate ions and wind with a single power source. As a result, a small, safe and easy-to-control ion detector suitable for carrying can be realized.

  Furthermore, in the ion detector 10 of Example 2, the voltage at the time of corona discharge in the airflow generator 620 is variable.

  Moreover, in the ion detector 10 of Example 3, the airflow generator 620 also serves as the ion generator 100.

  Moreover, in the ion detector 10 of Example 4, it has the space for accelerating the ionization of a to-be-measured molecule between the ion generation part 100 and the ion filter part 200. FIG.

  In addition, although the said embodiment demonstrated the case where the ion generating part 100 had a some electrode, it is not limited to this, The ion generating part 100 may have one electrode.

  DESCRIPTION OF SYMBOLS 10 ... Ion detection apparatus, 100 ... Ion generation part (ion generator), 200 ... Ion filter part (ion filter), 600 ... Detection part, 610 ... Detector, 620 ... Airflow generator, 621 ... Single power supply, 900 ... control unit.

US Patent Application Publication No. 2015/0028196 Japanese Patent No. 40636676 Japanese Patent No. 5221954

Claims (7)

An ion generator for ionizing a molecule to be measured;
An ion filter for selecting ions ionized by the ion generator;
A detector for detecting ions selected by the ion filter;
An ion detector comprising: an airflow generator that generates a flow for transferring ions ionized by the ion generator toward the ion filter by corona discharge.   The ion detection apparatus according to claim 1, wherein the airflow generator includes two or more electrodes and a flow path penetrating the airflow generator.   The ion detector according to claim 1, wherein the airflow generator has a variable voltage during corona discharge.   The ion detector according to claim 1, wherein the air flow generator also serves as the ion generator.   5. The ion detector according to claim 1, wherein the airflow generator has a single power source for generating ions and generating wind.   The ion detection apparatus according to claim 1, wherein a space for promoting ionization of the molecule to be measured is provided between the ion generator and the ion filter.   The ion detector according to claim 1, wherein the ion generator includes one or more electrodes.

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