JPH0992200A - Plasma ion source mass analysis device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct variation of ionization efficiency and try to improve measurement precision by correcting a signal used for measurement, using molecule or element ion peak of gas which is generating a plasma instead of an element targeted for measurement. SOLUTION: A sample separated by elements by means of a mass analysis gauge 24 is deflected by 90 degrees by means of a deflecting electrode 26, led by an ion detector 28, and detected. Another ion detector 62 is set at the back of the deflecting electrode 26, and molecule or element ion peak of gas which is generating a plasma instead of an element targeted for measurement is detected. This signal is amplified by using an amplifier 64, and a signal to be measured by means of an ion detector 28 is corrected by using that signal. Thus, variation of ion effect ratio at a torch, and variation of ion convergence efficiency due to the dirt of an ion lens through long-duration use and the like can be corrected. In addition, an optical detection means is provided, a molecule or element emitting ray of gas which is generating a plasma is detected, and the measurement signal of the ion detector 28 is corrected by means of that signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma ion source ultratrace element having a plasma produced by various methods as an ion source and a quadrupole mass spectrometer or a double-focusing mass spectrometer as a detector. Regarding analytical equipment.

[0002]

2. Description of the Related Art Conventional techniques are discussed, for example, in Koji Kawaguchi and Taketoshi Nakahara, edited by Spectroscopic Society of Japan, Series 28, "Plasma Ion Source Mass Spectrometry", paragraphs 19 to 43. That is, the plasma ion source mass spectrometer is configured to ionize a solution sample by plasma, draw the resulting ions into a vacuum through an interface, and perform measurement by a mass spectrometer.

[0003]

However, in the above-mentioned prior art, the object to be measured is ions that have been mass fractionated by the quadrupole mass spectrometer and then guided to the detector. For example, fluctuations in ionization efficiency in the torch, There was no means to correct for fluctuations in the device such as fluctuations in ion focusing efficiency due to dirt on the ion lens due to long-term use. The internal standard method is one means for solving the above problems from the standpoint of a measurer. For example, Koji Kawaguchi and Taketoshi Nakahara, Japan Spectroscopy Society
Measurement method series 28 "Plasma ion source mass spectrometry"
, Paragraphs 110-115 of. This method corrects for instrumental fluctuations by adding a fixed concentration of a non-measuring element (element that does not require measurement) to the measurement sample in advance and measuring the element at the same time. Is the way to try. However, when using this internal standard method, it is necessary to add a certain concentration of sample to the measurement sample, it is a very time-consuming method, and it is necessary to give sufficient consideration to contamination of the added sample. , In the case of multi-element measurement, it is difficult to search for an element that does not need to be measured, and in the measurement of trace metal elements in organic solvent-based samples, it is very difficult to search for a stable additive element itself. However, there were numerous problems in using the internal standard method.

The object of the present invention is to improve the ion focusing efficiency due to, for example, fluctuations in ionization efficiency of a torch and contamination of the ion lens due to long-term use, without requiring the measurer to perform troublesome processing such as the internal standard method. It is an object of the present invention to provide a plasma ion source mass spectroscope capable of compensating for instrumental fluctuations such as fluctuations.

[0005]

The feature of the present invention for solving the above-mentioned problems is that, in addition to an ordinary detector used for measurement, an additional ion detecting means or optical detecting means is provided. This detection means is not the element to be measured contained in the measurement sample, but the molecule of the gas generating plasma or the element peak of the ion or the emission line of the gas molecule or the element generating the plasma. It is about correcting the signal to be used. The plasma used in the plasma ion source mass spectrometer is usually ICP.
(Inductively coupled plasma) or MIP (microwave inductive plasma) is used. Ar (Argon) for ICP
In the gas, MIP, N ₂ (nitrogen) gas is used as a plasma generation gas, so that molecules or elemental ions derived from argon or nitrogen are generated in plasma. Since these molecules or elemental ions are the main substances that generate plasma, the number of them is so large that they are incomparable with the number of ions to be measured (usually 5 to 6 digits or more), and It cannot be detected by the usual detector used. Therefore, it must have an additional ion detection means or optical detection means other than the ordinary detector used for measurement (these are generally much lower in sensitivity than ordinary detectors used for measurement). To detect the molecular or element ion peak of the gas generating plasma or the emission line of the molecule or element of the gas generating plasma and use this signal to correct the signal used for measurement To do.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. As an example, FIG. 1 shows the overall configuration of a microwave plasma trace element analyzer. Here, 1 is a sample to be measured. Usually, 2 is a liquid and is supplied to an atomizer 6 such as a nebulizer through a capillary tube 4. A carrier gas 8 is supplied to an atomizer 6 such as a nebulizer, where the sample is atomized. If 2 is a liquid, it may be an aqueous solution or an organic solvent such as alcohol. This atomized sample is a microwave plasma 1 generated by microwaves.
The sample, which is guided to No. 8 and atomized by the microwave plasma 18, is dissociated, atomized, and ionized, and is emitted into the atmosphere. A gas controller 50 is provided to atomize the sample under an appropriate condition with an atomizer 6 such as a nebulizer, and to guide the atomized sample to the plasma 18. Are sent to the plasma 18. The gas control unit 50 is controlled by the control computer 52. Plasma generator 1
A plasma 18 is generated at 2, and a microwave 14 is used for this. The microwave 14 is generated by the microwave power source 54 as 2.45 Ghz and the plasma generation unit 12
Supplied to. A plasma 18 is generated in the atmosphere by the microwave 14 and the plasma gas 16, and the temperature of the plasma 18 reaches about 5000 ° C to 6000 ° C. The microwave power supply 54 is controlled by the control computer 52 so as to have optimum conditions. Here, the sample ionized by the plasma 18 in the atmosphere is guided to the mass spectrometric section for mass analysis. Since the mass spectrometer 24 operates in vacuum, the ionized sample is efficiently drawn into the vacuum. In addition, an interface system (sampling cone and skimmer cone) 20 is provided.
The interface system 20 is usually made of metal such as copper or nickel that can be cooled well. The interface system 20 draws the sample ionized in the plasma. Since the mass spectrometer 24 operates in a vacuum (about 10 ⁻⁶ Torr) environment, this device is equipped with 34,
Vacuuming is performed in three stages of 30, 32, that is, operating exhaust is performed. For vacuum evacuation, 34 is usually a rotary pump, 30, 32
Is performed by a combination of turbo molecular pump + rotary pump or a combination of oil diffusion pump + rotary pump. These vacuum pumps are also controlled by the control computer 52, and evacuation is automatically performed. Interface system (sampling cone and skimmer cone) 2
The ionized sample drawn through 0 into the vacuum is focused by an ion lens 22 controlled by a control computer 52 onto a quadrupole mass spectrometer 24. The ion lens 22 is supplied with a voltage by the ion lens power supply 56 and can control the behavior of the flow of ions having electrical properties. Quadrupole mass spectrometer 24
The ions introduced into the are classified by element by the quadrupole mass spectrometer 24. The quadrupole mass spectrometer 24 can take out any element by controlling the power source 58 for driving the mass spectrometer by the control computer 52. In a normal measurement, the sample sorted by element by the quadrupole mass spectrometer 24 is then deflected by 90 degrees by the deflection electrode 26, guided to the ion detector 28, and detected. This signal is amplified using a method called pulse counting that can detect each incident ion.
0 to obtain the data. This method allows very sensitive measurements. In the present invention, another ion detector 62 is installed behind the deflection electrode 26, and the ion detector 62 detects not the element to be measured but the molecule or element ion peak of the gas generating plasma. In the normal case, the number of gas molecules or elemental ions that generate plasma is an order of magnitude larger than the number of elemental ions to be measured (larger by 5 digits or more). Therefore, the ion detector 62 is an ion detector. A Faraday cup or the like, which is far less sensitive than 28, is used, but this detector is not limited to the Faraday cup and any detector can be used. The signal from the Faraday cup is amplified using the amplifier 64 to obtain data. Although the signal from the Faraday cup is used to correct the measurement signal measured by the ion detector 28, two mass numbers cannot be measured at the same time when using the quadrupole mass spectrometer 24. Therefore, as shown in Fig. 2, the peaks are scanned at high speed in a time division manner,
The signals of the element to be measured and the molecular ion signals of the gas generating plasma are alternately captured, and then the correction process is performed. In FIG. 2, 70 represents a time axis, and 72 represents a mass number scanned by the quadrupole mass spectrometer (acquiring data).
As an example, 74 is a mass number that captures data of elemental ions to be measured, and 76 is a mass number that captures data of molecules or elemental ions of gas that is generating plasma. Both signals are fetched at intervals of, for example, 50 msec 78, but of course, this fetching interval may be an arbitrary value without any problem. In this way, the peaks are scanned at high speed in a time-divisional manner, and the data is alternately fetched so that the signal to be corrected is probable and corrected. By performing the correction in this way, for example, the fluctuation of the ionization efficiency in the torch, the fluctuation of the ion focusing efficiency due to the contamination of the ion lens due to long-term use, and the like, the signal of the element to be measured is also the gas generating plasma. Since it similarly affects the signal of the molecule or element ion, the influence can be corrected.

Next, as another embodiment, a further one
A method of correcting the signal used for the measurement using the individual optical detecting means will be described with reference to FIG. 3 has the same basic configuration as that of FIG. 1, but an optical detection means 80 is provided in front of the interface system (sampling cone and skimmer cone) 20. This optical detecting means 8
0 is an optical fiber, and any means can be used as long as it can transmit light to the spectroscope 82. And the spectroscope 82
The light separated by is guided to the detector 84. With this configuration, the emission line of the molecule or element of the gas generating plasma, not the element to be measured, is detected. In the usual case, the emission of molecules, elements, or ions of the gas that generates plasma is orders of magnitude higher than that of the elemental ion to be measured, but the sensitivity due to normal emission is much worse than the sensitivity of the mass spectrometer. Therefore, it does not matter. This light emission signal is amplified by the amplifier 86 to obtain data.
This signal is used to correct the measurement signal measured by the ion detector 28, and this means is the same as the correction method using the signal from the Faraday cup described above. However,
In this case, the optical detection means and the element to be measured can be measured at exactly the same time, so that the time-divisional measurement as shown in FIG. 2 is not necessary.

The effect of the present invention will be described with reference to FIG. FIG. 4 shows the effect of the correction by the signal from the Faraday cup described in the first half of the embodiment.
In FIG. 4, the horizontal axis represents time and the vertical axis represents signal intensity. The abscissas 108, 110, 112 represent time, and represent the progress of measurement. Further, the vertical axis 102 shows the signal output from a normal detector used for measurement, the vertical axis 104 shows the signal output from the Faraday cup, and the vertical axis 106 shows the result of correcting the signal of 102 with the signal of 104. ing. In this figure, in the area (time area) 114, 1
The 02 signal is stable and needs no correction in this region. However, in the regions 116 and 118, the signal of 102 is shifted up or down from the value that it should be. Although it is schematically shown here, in an actual mass spectrometer, due to fluctuations in the ionization efficiency of the torch, fluctuations in the ion focusing efficiency due to contamination of the ion lens due to long-term use, and other fluctuations in the equipment, A signal value will be obtained with a deviation from a desired value. Reference numeral 106 serves to cancel these fluctuations. Specifically, for example, the signal of 102 is divided by the signal of 104, and the resulting ratio is used.

[0009]

EFFECTS OF THE INVENTION According to the present invention, ion converging due to fluctuations in ionization efficiency of a torch and contamination of an ion lens due to long-term use can be achieved without requiring a measurer to perform troublesome processing such as the internal standard method. It is possible to correct apparatus-like fluctuations such as efficiency fluctuations, and it is possible to greatly improve the measurement accuracy in sample measurement.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a method of data acquisition in the embodiment in FIG.

FIG. 3 is a block diagram of a second embodiment of the present invention.

FIG. 4 is an explanatory view showing the effect of the present invention.

[Explanation of symbols]

24 ... Quadrupole mass spectrometer, 26 ... Deflection electrode, 28 ... Ion detector, 62 ... Faraday cup, 80 ... Optical detection means.

Claims (2)

[Claims] 1. A plasma ion source ultratrace element analyzer including a plasma generation system, a plasma torch system, a sample introduction system, an ionization system, an interface system, and a mass spectrometry system,
In addition to the usual detector used for measurement, it has a detector for one additional ion, and the detector is not the element to be measured contained in the measurement sample but the molecule or element ion peak of the gas generating plasma. A plasma ion source mass spectrometer, characterized in that it is used to correct a signal used for measurement. 2. The method according to claim 1, further comprising one optical detecting means other than a normal detector used for measurement, wherein the optical detecting means is not an element to be measured contained in a measurement sample but plasma. Plasma ion source ultratrace element analyzer that corrects the signal used for measurement by using the emission lines of the molecules or elements of the generated gas.