JP2000340170A - Mass spectroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized mass spectroscope capable of sepersensitively measuring a mixed component in a liquid or gaseous sample. SOLUTION: In this mass spectroscope, a quadrupole ion trap type mass spectrometer is used. While only ions of a component A or mixed component containing the ions of the component A are made incident on an ion trap, only the ions of the component A are accumulated by using the ion trap. Then, upon changing over a switch to stop applying an alternating current electric field for accumulating the ions, a DC electric field pointing from an ion inlet 5 to an ion outlet 6 is formed. The accumulated ions are discharged from the ion outlet 6 to be detected by a detector 50.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separation analyzer for ionizing components present in a liquid sample or a gas sample and performing mass spectrometry. The present invention also relates to an analyzer for introducing a liquid sample or a gas sample without using a separation unit, ionizing components present in the liquid sample or the gas sample, and performing mass spectrometry.

[0002]

2. Description of the Related Art Liquid chromatography (Liquid chromatography) is used to separate mixed components present in a liquid sample or a gas sample.
Chromatography (LC) and gas chromatography (Ga)
s Chromatography (GC) and Capillary Electrophoresis (CE). An analysis method combining these separation methods and mass spectrometry (MS) having excellent substance identification capability, that is, liquid chromatography / mass spectrometry (Li
quid Chromatography / Mass Spectrometry, LC
/ MS), Gas Chromatography / Mass Spectrometry (hereinafter abbreviated as GC / MS), Capillary Electrophoresis / Mass Spectr
(hereinafter, abbreviated as CE / MS) is used for analysis in many fields.

In a typical LC / MS apparatus, a component in a liquid sample flowing out of an LC is ionized by using an atmospheric pressure ionization method such as an electrospray method or a sonic spray method, and is subjected to a quadrupole ion trap (hereinafter, referred to as a quadrupole ion trap). , Simply referred to as an ion trap) mass spectrometer.
The ion trap mass spectrometer is characterized by high sensitivity because ions can be accumulated in the ion trap.

[0004] The principle of the ion trap will be briefly described. A rotating hyperboloid ion trap, which is a typical ion trap, includes a ring electrode and two end cap electrodes. At the center of the two end cap electrodes, an ion inlet and an ion outlet are opened. Between the end cap electrode and the ring electrode, an AC voltage having an amplitude Vac and a frequency Ω and a DC voltage Vdc are applied in a superimposed manner. Of the ions incident on the ion trap,
Ions satisfying the stability conditions described later are trapped inside the ion trap, and the other ions are ejected outside.

FIG. 11 is a diagram showing conditions for stabilizing ions. Assuming that the inner diameter of the ring electrode is 2r and the frequency of the AC voltage is Ω, the ions A and B have a point (q, a) determined by the ratio between their mass number m and valence z and the value of m / z = (4zeVac
/ Mr ² Ω ² , -8zeVdc / mr ² Ω ² ). A = −2 (Vdc / Vac) between the above a and q
There is a relationship of q.

When the point (q, a) exists in the shaded area in the figure, the ion makes a stable periodic motion in the internal space of the ion trap. Otherwise, the movement of the ions is unstable and is eventually ejected out of the ion trap. When Vdc = 0V, the straight line a =
-2 (Vdc / Vac) q overlaps the q-axis. In this case, Vac
An ion having an m / z larger than a specific m / z determined by the above satisfies the stability condition and is captured by the ion trap. Hereinafter, such an ion trapping mode will be referred to as a multi-ion mode. On the other hand, if Vdc and Vac are set to appropriate values, as shown by the straight line 1 in the figure,
For example, only ion A can be captured. Such a mode in which one kind of ions is substantially accumulated is hereinafter referred to as a single ion mode.

Known Example 1 (Analytical Chemistry,
(1991, Vol. 63, p. 375) describes an ion trap type mass spectrometer in which the amplitude of an AC voltage is scanned to destabilize accumulated ions, discharge the ions from an ion trap, and sequentially detect the discharged ions. LC / M using a meter
S is disclosed. In this apparatus, after accumulating ions in the multi-ion mode, the amplitude of the AC voltage is scanned toward the higher voltage side, whereby detection is performed in ascending order of m / z, and a mass spectrum can be obtained. However, in this method, about half of the accumulated ions are discharged from the ion inlet side and do not reach the detector. In addition, there are variations in arrival times at the detector due to variations in ion positions and velocity vectors at the time of voltage scanning.

On the other hand, a known example 2 (Japanese Patent Laid-Open No. 8-32)
9882), by superimposing a pulsed DC electric field while capturing ions using an AC electric field,
An apparatus for discharging ions is disclosed. In this device, ions are ejected in one direction, so that all ions reach the detector. Also, there is little variation in arrival times at the detector.

Further, a known example 3 (J. Am. Soc. Mass)
Spectrom., 1996, Vol. 7, p. 1009) states that the application of an alternating electric field is stopped and the pulsed D
Disclosed is a time-of-flight mass spectrometer that uses a time-of-flight measurement to acquire a mass spectrum of the ejected ions after forming a C electric field and ejecting the ions. In this device, there is less variation in the time at which ions reach the detector than in the device of the known example 2.

[0010]

In the apparatus of the above-mentioned prior art example 1, the time at which the ejected ions reach the detector is larger than that of the apparatuses of the above-mentioned prior art examples 2 and 3, so that the SN ratio is inferior. . On the other hand, in the method of Known Example 3,
Although the SN ratio is higher than that of the method of the known example 1, the length is 150 c
The apparatus is large and expensive because it has a flight time measuring unit of about m.

[0011]

According to the present invention, after a specific measurement component is accumulated using a single ion mode, the application of an AC electric field is stopped and the DC electric field is reduced, as disclosed in the prior art 3. By forming, ions are discharged and detected. In this method, since the m / z discrimination has already been performed at the time of ion accumulation, the time-of-flight measurement unit is not required.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of the configuration of a central portion of a mass spectrometer of the ion trap type according to the present invention and an example of a measurement sequence. The ion trap includes a ring electrode 2 and two end cap electrodes 3 and 4. This ion trap is of a so-called rotary dipole type, but an ion trap of another shape can also be used. 50 is an ion detector located on the ion emission side.

At the center of the end cap electrodes 3 and 4,
An ion inlet 5 and an ion outlet 6 are opened, respectively. The size of the ion trap is such that the inner diameter of the ring electrode 2 is 14 mm and the distance between the end cap electrodes 3 and 4 is 14 m.
m, inner diameter of ion inlet and ion outlet is 2mm each
It is. These sizes are only examples.

A damping gas (usually using helium gas) is introduced from the gas pipe 7 into the ion trap.
The damping gas has a role of reducing the orbital amplitude of the captured ions and converging the orbit to the center of the ion trap.

When accumulating ions, an AC voltage and a DC voltage are applied to the ring electrode 2 in a superimposed manner.
And 4 are maintained at 0V (ground potential). When the ions are ejected, the switch 10 is switched so that the DC voltage V1 is applied to the ring electrode 2 and the DC voltage V2 is applied to the end cap electrode 3. When the ions to be detected are positive ions, V2>V1> 0, and when the ions to be detected are negative ions, V2>V1> 0.
<V1 <0. Usually, V2 is twice V1.
This need not be the case. The absolute value of V2 is, for example, 300V. If the voltage value is too large, the ions are accelerated too much, and the probability of dissociation of the ions due to collision with the damping gas increases.

The method of applying a voltage to each electrode and the control method for switching the voltage are not limited to the methods shown here.
It is only necessary to be able to switch between an AC electric field for accumulating ions and a DC electric field for discharging ions.

While the mixed component including the component A or only the component A is incident on the mass spectrometer, the DC voltages Vdc and Vac applied to the ring electrode 2 are changed as shown by a straight line 1 in FIG. The condition of the single ion mode for capturing only A is set. After accumulating ions for a certain period of time under these conditions, the application of the AC electric field is stopped, and the DC
An electric field is formed, ions are ejected from the ion trap, and the ions are detected by the detector 50.

When ions are ejected by scanning the amplitude of the AC voltage to eject ions (hereinafter, referred to as an AC voltage scanning method), the trapped ions are centered on the center of the ion trap. While reciprocating in the z-direction, the amplitude gradually increases, and is eventually discharged through the ion discharge port (or ion introduction port). in this case,
The velocity of the ions is highest near the center, and the velocity in the z direction is zero near the ion outlet or ion inlet. Therefore, at the ion discharge port and the ion introduction port, the movement of ions is likely to bend in the inner diameter direction of the ring electrode under the influence of the curvature of the electric field, and the discharged ion beam diverges greatly.

In the conventional apparatus, mesh-shaped electrodes are usually provided on the ion introduction port and the ion discharge port in order to reduce the distortion of the electric field between the ion introduction port and the ion discharge port. As the mesh, for example, a mesh in which metal lines such as tungsten are arranged vertically and horizontally at equal intervals, or a mesh in which minute holes are densely formed by etching a metal plate are used.

On the other hand, in the method of the present invention, the ejected ions gradually increase in speed and reach the maximum speed at the ion outlet. Therefore, the effect of the electric field curvature at the ion outlet is small, and therefore, there is an advantage that a mesh is not necessarily required.

FIG. 2 shows a simulation result of the detector output when the AC voltage scanning method is used. FIG. 3 shows the size of the rotating hyperboloid ion trap used in the above simulation. The inner diameter of the ring electrode 2 was 14 mm, the distance between the two end cap electrodes 3 and 4 was 14 mm, the diameter of the ion inlet and the outlet of the ion was 2 mm, and mesh electrodes were provided. However, in the simulation, the mesh electrode is replaced with an electrode having a transmittance of 100%, and thus, the curvature of the electric field at the opening is ignored.

An AC voltage having a frequency of 800 kHz and an amplitude of Vac is applied to the ring electrode 2, and ions having m / z = 1000 and an initial energy of 0 are arranged at one of four points a to d shown in FIG. Emitting the above ions out of the ion trap,
Detector 100mm away from ion trap (not shown)
The time to reach was calculated. This was performed 100 times for each of the points a to d, and graphed.

FIG. 2 shows the result when Vac = 3000V. From this figure, it can be seen that the time from when the ions start to reach the detector to when all the ions have finished arriving (hereinafter, referred to as emission time) is about 10 microseconds. When Vac is reduced, the emission time gradually increases,
For example, when Vac = 2652V, it is about 600 microseconds. When Vac is further reduced, the stability condition is satisfied, and ions are not emitted while being trapped. On the other hand, when Vac is increased, for example, when Vac = 4000 V, the emission time is reduced to about 7 microseconds. However, ions that do not reach the detector after colliding with the electrodes account for about 10% of the total. Therefore, in the AC voltage scanning method, it is considered that the ion emission time is as short as about 10 microseconds. In the AC voltage scanning method, the minimum value of the emission time does not depend on m / z in principle. The emission time hardly changed even when the initial energy was taken into consideration.

FIG. 4 shows the calculation result of the ion emission time in the method of the present invention. The emission time was determined as the difference between the arrival times of the ions at the initial energy of 0 at points b and e in FIG. 3 with a uniform gradient electric field formed in the internal space of the ion trap. . The position of the detection surface was 100 mm from the ion trap. From FIG. 4, for example, m / z
It can be seen that, for ions of = 1000, when the voltage between the end cap electrodes is 300 V, the emission time is about 1.1 microseconds, which is about 1/10 of that in the case of the AC voltage scanning method. The emission time depends on the voltage between the end cap electrodes. If the voltage is reduced, the emission time becomes longer. For example, even at 150 V, the emission time is about 1.6 microseconds, which is one fifth of the AC voltage scanning method. It is as follows.

Since the temperature inside the ion trap is about 200 ° C., the initial energy of ions is 1
It is estimated to be about 00 meV. When the variation of the initial energy is ± 100 meV, the emission time is 20 to 30.
Only increase by about%.

The emission time is different from the AC voltage scanning method and largely depends on m / z. The emission time becomes longer as m / z is larger. However, in the AC voltage scanning method,
The upper limit (mass range) of the measurable m / z is about 2000, and in this mass range, the emission time of the method of the present invention is shorter than that of the AC voltage scanning method.

FIG. 5 shows a calculation result of the dependence of the ion emission time on the position of the detector in the method of the present invention. In the figure, the voltage between the end cap electrodes = 300 V, m / z =
The case of 1000 and initial energy = 0 is shown. From FIG. 5, the emission time has a minimum value of 0 when the detector position is about 13 mm. Hereinafter, the detector position at which the emission time becomes 0 will be referred to as a spatial convergence surface. If the detector position is adjusted to the spatial convergence plane, the emission time can be made almost zero, and the actual emission time can be reduced to about 3 due to the dispersion of the initial energy.
It can be reduced to 00 nanoseconds. On the contrary,
In the case of the AC voltage scanning method, it was found from the results of the simulation that the difference in the position of the detector hardly affected the emission time.

Therefore, according to the method of the present invention, the emission time can be set to about 3% of that of the AC voltage scanning method.
Further, in consideration of the fact that about half of the accumulated ions are discharged from the ion inlet in the AC voltage scanning method, the method of the present invention achieves a detection sensitivity about 60 times that of the AC voltage scanning method.

Incidentally, a high voltage of about 3 kilovolts is normally applied to a multi-channel plate (MCP) usually used for ion detection. Therefore, when the degree of vacuum is low, there is a problem that normal operation is not performed due to discharge. Usually, the degree of vacuum inside the ion trap is set to about 10 ^-3 Torr which is necessary for capturing ions and converging the orbital amplitude. The degree of vacuum outside the ion trap is maintained at about 10 ^-5 to 10 ^-6 Torr, which is necessary for operating the MCP. However, the degree of vacuum decreases closer to the ion outlet. Therefore, in reality, the detector is 13 mm from the ion trap.
Can not be placed at a distance of Therefore, usually, an accelerating electric field is provided between the ion trap and the detector, and the well-known principle of the two-stage acceleration method is used to bring the space converging surface to a position where the degree of vacuum is sufficiently high, for example, an ion trap. Is formed at a position 50 to 100 mm away from the sensor, and a detector is arranged at that position.

FIG. 6 shows the configuration of a part of an ion trap type mass spectrometer using a two-stage acceleration method using an ion trap composed of plate electrodes. Ion trap 31
Is composed of two end cap electrodes 34 and 35 and two ring electrodes 32 and 33. The ring electrodes 32 and 33 are disk-shaped electrodes having a thickness of about 0.5 mm. The end cap electrodes 34 and 35 are formed by making holes of about 2 mm as an ion introduction port and an ion discharge port at the center of a disk-shaped electrode having a thickness of about 0.5 mm.

In the ion trapping mode, the two ring electrodes 32 and 33 have the same potential, and a DC voltage and an AC voltage are applied in a superimposed manner. In the ion discharge mode, the end cap electrode 34, the ring electrode 32, the ring electrode 33, and the end cap electrode 35 have voltages V1, V2,
V3, V4 (V1>V2>V3> V4 or V1 <V2
<V3 <V4) is applied.

At the subsequent stage of the ion trap, plate-shaped accelerating electrodes 36 to 38 for forming an accelerating electric field are arranged. When the voltage applied to the ion trap and the accelerating electrode is set so that the magnitude of the electric field of the gradient electric field (accelerating electric field) in the ion trap and the electric field of the accelerating electric field in the subsequent stage are the same, the voltage in the ring part except for the electrodes at both ends is obtained. The curvature of the electric field can be eliminated.

For example, the distance between the two end cap electrodes is 14 mm, the length of the accelerating electric field is 14 mm, the inclined electric field and the subsequent accelerating electric field in the ion trap are uniform, and the magnitude of both electric fields is When the applied voltage value to the ion trap and the accelerating electrode is set so that
The space focusing surface is formed at a position about 56 mm from the outlet of the ion trap. The use of a disk-type ion trap has the advantage that a uniform electric field can be formed in the ion trap and in the subsequent acceleration region. Therefore, better spatial convergence can be realized as compared with the case of using a rotating dipole surface ion trap, and therefore, an emission time closer to the calculated value can be realized. Note that the number of accelerating electrodes is not limited to three.

FIG. 7 shows the configuration of an LC / MS device according to the present invention. The liquid flowing out of the LC 41 is introduced into the ion source 43 through the pipe 42. Here, ions of the components present in the droplet are generated. In the ion source 43, for example, an atmospheric pressure ionization method such as an electrospray method or a sonic spray method is used. The generated ions are
Introduced into the vacuum chamber 44, the accelerating electrode 45, the focusing electrode 4
6. The light passes through the deflection electrode 47 and the gate electrode 48 and is introduced into the ion trap 1.

The ions discharged from the ion trap 1 pass through the gate electrode 49 and are detected by the detector 50. The vacuum chamber 44 is divided into a differential evacuation unit 51 and an analysis unit 52, and is evacuated by vacuum pumps 53 and 54, respectively. The inside of the ion trap 1 is usually maintained at a vacuum degree of about 10 ^-3 Torr. The degree of vacuum around the detector 50 in the analyzer 52 is controlled to about 10 ^-5 to 10 ^-6 Torr because the detector 50 needs to operate stably.

The longer the switching time from the ion trapping mode to the ion discharging mode, that is, the longer the time from the stop of the AC electric field to the complete rise of the gradient electric field, the greater the variation in the position of the ions. Becomes longer. A rise time of the DC voltage for the gradient electric field of about 1 microsecond can be realized relatively easily. For the emission time in the ideal case where the rise time is 0,
When the rise time is 1 microsecond, the increase in the emission time is only about several percent, and does not have a serious effect. The lower limit of the rise time is mainly determined by the size of the capacitance component of the electric circuit system including the ion trap and the electrodes around the ion trap, but about 10 nanoseconds can be technically realized.

FIG. 8 shows a time sequence of voltage application to each electrode of the ion trap and the entrance and exit gate electrodes. The role of the entrance-side gate electrode is to pass ions into the ion trap and introduce them into the ion trap in the ion trapping mode, and to block noise in the ion discharge mode to reduce noise.

The exit side gate electrode substitutes a part of the acceleration electrode. The role of the exit-side gate electrode is to prevent the passage of ions in the ion trapping mode and prevent ions that do not satisfy the trapping condition from reaching the detector, thereby saturating or fouling the detector. , In ion ejection mode,
Functions as a part of the acceleration electrode. Immediately before switching from the ion trapping mode to the ion discharging mode, the passage of ions is stopped by the entrance side gate electrode for an appropriate time,
Ions that do not satisfy the capture conditions, that is, noise components,
Noise can be reduced by exclusion from the space within the ion trap and between the ion trap and the detector.

The time in the ion trapping mode is Tt, the time in the ion discharge mode is Td, the concentration of the target component in the sample solution is C, the flow rate of the sample is F, and the ratio at which the target component is trapped in the ion trap is P1, Assuming that the rate at which the detected ions reach the detector is P2, the amount of ions Nt accumulated in the ion trap is expressed as Nt = C · F · Tt · P1, and the amount of ions Nd that can be detected is expressed as Nd = Nt · P2. Is done. In LC, since the half width of each component peak is about several seconds, in order to reproduce the peak shape and secure good quantitative performance, T
It is necessary to set t to about 1 second or less.

By the way, in the region where Tt is short, Nd is Tt.
, The longer the Tt, the better the sensitivity.
If t becomes longer than a certain level, there is a problem that Nd is saturated. This is because the amount of accumulated ions is too high,
This is because the spatial distribution of ions becomes larger than the diameter of the ion outlet. Nt and Nd can be increased by increasing the diameter of the ion inlet and the ion outlet, which are usually 2 to 3 mm, but in reality, when the diameter increases, the degree of vacuum around the detector decreases, and There is a problem that interferes with the operation of the container.

Under the condition where Nd is saturated, there is a problem that the quantitativeness of measurement is impaired. Therefore, it is important to set Tt as large as possible in a range where Nd does not saturate according to the size of C or F. On the other hand, Td
Depends on the m / z of the component to be measured, the position of the detector, and the acceleration voltage value, but 1 ms is sufficient. For example, the position of the detector is relatively 100 mm away from the ion trap, and the voltage for the gradient electric field is 150 V, which is relatively small.
In this case, the time required for ions of m / z = 1000 to reach the detector is only about 50 microseconds.

In the LC, the half width of each component peak is usually several seconds to several tens of seconds. Therefore, the data acquisition interval required to accurately reproduce the peak shape is about 1 second or less. When Tt is shorter than this data acquisition interval, the SN ratio can be improved by integration. For example, when the data interval is 1 second and the operation cycle of the ion trap is 100 milliseconds, the SN ratio can be improved to √10 times by integrating 10 measured values.

A method of operating the apparatus when performing simultaneous analysis of pesticides contained in river water using the LC / MS of the present invention will be described. For the sake of simplicity, it is assumed that there are only two types of pesticides A and B that can be separated by LC in the river water. The retention time of A and B, the m / z of each ion generated from A and B, and the calibration curve are obtained in advance by library search or preliminary experiment.

As the mobile phase of LC, water / methanol obtained by mixing water (pure water) and methanol in equal amounts is used. In this case, the m / z of the component ions derived from the mobile phase is several tens or less, while the m / z of the currently used pesticide is 100 to 100.
There are between 400. Therefore, the ion trap can be set to the multi-ion mode in which the pesticides A and B are captured, but the component ions derived from the mobile phase are not captured. In this method, there is no theoretical upper limit for the m / z value of an ion that can be measured. Therefore, it is possible to measure even a component exceeding m / z = 2000 which cannot be measured by the AC voltage scanning method.

While the pesticides A and B are eluted, A and B respectively
It is also possible to set a single ion mode in which only the ions are captured. In this way, accumulation of noise ions other than the measurement component can be significantly reduced. Agrochemical A
This operating method is also effective when there is a component in the sample that differs in m / z from (or B) but is not separated by LC.

When measuring components other than pesticides, the m / z of ions derived from the mobile phase may be larger than the m / z of component ions to be measured. In this case, by using the above-described operation method using the single ion mode, ions derived from the mobile phase can be excluded, so that the SN ratio can be significantly improved.

When measuring a known substance such as a pesticide,
Since the elution time of each component in the LC is known in advance, the time except for the time when each component is eluted is prevented by using the entrance-side gate electrode to prevent the passage of ions, thereby preventing contamination of the ion trap and the detector. Can be reduced.

When a sample contains a plurality of components that cannot be separated by LC, or when a sample containing a plurality of components is
An operation method in the case of performing mass spectrometry without separation by, for example, will be described below.

When the number of components that are not separated from each other by LC is n, the accumulation time is divided by n, and each component is measured in the single ion mode. Such an operation mode is called a time division mode. On the other hand, an AC voltage scanning method, that is, a mode in which a plurality of ions are simultaneously accumulated in the multi-ion mode, and then the mass spectrum is measured by scanning the amplitude Vac of the AC voltage can be used.

The sensitivity comparison between the time division mode and the AC voltage scanning method will be described below. As described above, the time division mode has an SN ratio several tens of times higher than that of the AC voltage scanning method due to the difference in ion emission time. However, in the following description, the SN ratio due to other factors will be described. The comparison will be described.

When the number of measurement components is n, in the time division mode, the accumulation time of each component is 1 / n of the AC voltage scanning method.
Therefore, if simply considered, the SN ratio is also 1 / n. However, in the AC voltage scanning method, impurities (non-measurement components) are accumulated at the same time in addition to all the measurement components, so that the ion trap is more likely to be saturated than in the time division mode. Further, in the case of the AC voltage scanning method, when the ion trap is saturated, the quantitativeness of all components is impaired.

Therefore, in such a case, the AC voltage scanning method is performed a plurality of times and the data is integrated. When the number of integration times is N and the number of measurement components is n, and the SN ratio in the case where no foreign matter is present is calculated, the ratio between the SN ratio in the time-division mode and the SN ratio in the AC voltage scanning method is Equation 1. In Expression 1, Ci is the concentration of the component i, and Cmax is the maximum value of the concentration of each component.

[0053]

√N / n (≦ √ (ΣCi / nCmax) ≦ 1) Therefore, the difference in the SN ratio due to the ion emission time,
Taking into account the presence of impurities, the time division mode may well exceed the AC voltage scanning method. When analyzing pollutants contained in tap water and river water, such as pesticides and environmental hormones, the tap water and river water contain many contaminants, so the time-sharing mode is particularly effective. There is.

In the time division mode, by adjusting the ratio of the accumulation time of each component, for example, the S
It is possible to detect by N ratio. As an example, a comparison of the S / N ratio with the AC voltage scanning method is shown for the case where the measurement components are A and B and no impurities are present. For example, when the concentration ratio of A and B is 10: 1, the SN ratio of components A and B can be made equal by setting the accumulation time of A and B to 1:10 in the time division mode. The S / N ratio in this case and the S / N ratio when integrating N times by the AC voltage scanning method
Compared with the N ratio, for the low concentration component B, the former is about ΔN times (N ≦ 12) (the maximum is about 3 times) the latter. As for the high concentration component, the latter is about 11 / √N of the former.
Times (up to about 3 times). When the concentration ratio increases to 100: 1, the ratio of the SN ratio of the former to the latter increases to about ΔN times (N ≦ 102) (up to about 10 times) for the low concentration components. As for the high concentration component, the latter is the former 101
/ √N times (up to about 10 times).

When analyzing pollutants contained in tap water or river water, for example, pesticides and environmental hormones, the approximate concentration of each component can be known empirically or experimentally. However, it is necessary to change the time-sharing method for each sampling point and each season because there is a difference in the sampling point of the sample and a change in concentration depending on the season. In contrast, for pollutants such as pesticides and environmental hormones in environmental water, legal reference concentrations are set for each substance, so it is more realistic to perform time-sharing according to the reference concentration of each substance. It is a target. If the component concentration exceeds the reference concentration and the ion trap saturates, reduce the distribution time for the component or dilute the sample and reanalyze. It should be noted that the concentration of a component that is significantly lower than the reference concentration and cannot be detected may be considered to be 0, and therefore does not need to be re-analyzed.

In the LC / MS, there is a problem that a charged droplet or a neutral droplet having no charge reaches the detector sporadically and generates a large noise. FIG. 9 shows the method (a) of the present invention and the AC voltage scanning method (b) during ion detection.
FIG. 4 is a conceptual diagram showing a comparison of the effects of single noise in the first embodiment. The method of the present invention has an advantage that the probability of single noise occurring during detection of measurement component ions is small because the ion emission time is shorter than that of the AC voltage scanning method.

FIG. 10 is a conceptual diagram showing a comparison of the effect of single noise between the method of the present invention and the AC voltage scanning method on a chromatogram. In the method (a) of the present invention, since noise appears relatively sporadically on the chromatogram, the noise can be easily identified, and the noise can be eliminated by performing appropriate data processing. On the other hand, in the AC voltage scanning method (b), noise frequently appears on the chromatogram, so that it is more difficult to exclude single noise than the method of the present invention.

Further, in the AC voltage scanning method, as described above, the ion trap is likely to be saturated, and the integration may be performed. The greater the number of integrations, the greater the number of occurrences of single noise during ion detection, and the effect becomes more serious. On the other hand, in the system of the present invention, there is no need to perform integration, or even if it is necessary, the effect of single shot noise is smaller since it is less than in the AC voltage scanning system.

Note that the LC / MS according to the present invention may be one that can use an AC voltage scanning method together. The above explanation is based on CE / GC using CE or GC instead of LC.
The same applies to MS or GC / MS.

[0060]

According to the present invention, it is possible to provide a compact mass spectrometer capable of measuring a mixed component in a liquid or gas sample with high sensitivity.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a main part of a mass spectrometer based on the present invention and an example of a measurement sequence.

FIG. 2 is a diagram showing a simulation result of a detector output when an AC voltage scanning method is used.

FIG. 3 is a sectional view of an electrode configuration showing the simulation conditions of FIG. 2;

FIG. 4 is a diagram showing a calculation result of an ion emission time in the method of the present invention.

FIG. 5 is a diagram showing a calculation result of a detector position dependence of an ion emission time in the method of the present invention.

FIG. 6 is a sectional view of a main part of a disk-type ion trap mass spectrometer.

FIG. 7 is a schematic sectional view showing an LC / MS device configuration according to the present invention.

FIG. 8 is a time sequence chart of voltage application to each electrode of the ion trap.

FIG. 9 is an explanatory diagram comparing the effects of single noise in the present invention and the conventional example.

FIG. 10 is an explanatory diagram comparing the effects of single noise of the present invention and a conventional example on a chromatogram.

FIG. 11 is a diagram showing stability conditions of an ion trap.

[Explanation of symbols]

2 ... Ring electrode, 3 ... End cap electrode, 4 ... End cap electrode, 5 ... Ion inlet, 6 ... Ion outlet,
7 gas pipe, 10 switch, 41 LC, 42 pipe, 43 ion source, 44 vacuum chamber, 45 accelerating electrode,
46: focusing electrode, 47: deflection electrode, 48, 49: gate electrode, 50: detector, 51: differential pumping section, 52: analyzing section, 53, 54: vacuum pump.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hideaki Koizumi 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo F-term in Central Research Laboratory, Hitachi, Ltd. 5C038 JJ06 JJ07

Claims (4)

[Claims] In a quadrupole ion trap mass spectrometer, after substantially storing only one kind of ions, the application of an AC electric field for accumulating ions is stopped, and then a DC is stored inside the ion trap. Forming an electric field to eject ions,
A mass spectrometer characterized by detecting. 2. A separation analyzer using the ion trap mass spectrometer according to claim 1. 3. When a plurality of measurement components having different mass numbers / valences are introduced into a mass spectrometer at the same time, while the measurement components continue to flow into the mass spectrometer or a part thereof is divided. The mass spectrometer according to claim 1, wherein the mass spectrometer is used for measuring each measurement component. 4. The mass spectrometer according to claim 3, wherein the measurement time is different for each measurement component.