JPH0737546A - Mass spectrometry - Google Patents

Abstract

PURPOSE:To facilitate mass spectrometry by performing the mass spectrometry after changing an objective element, provided in a filament, into oxidized object in the oxidizing atmosphere, so that the element can be ionized. CONSTITUTION:A cryopump 2a, turbomolecular pump 2b and a rotary pump 2c are connected to a vacuum chamber, to vacuum-exhaust its inside. Then by a mass flow meter, air is introduced into the vacuum chamber via an air introducing pipe, to lower down a vacuum degree. In a condition of holding this vacuum degree, a filament is electrified from a DC power supply in the oxidizing atmosphere, to oxidize zinc in a filament surface into zinc oxide. After ending electrification, introducing air is stopped to increase the vacuum degree by again using an exhausting pump 2, and when the filament is electrified, a zinc ion can be detected by a prescribed current value. Then by oxidizing just before analysis, ionization can be performed, and mass spectrometry can be facilitated.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a mass spectrometry method,
More specifically, the present invention relates to a mass spectrometric method capable of accurately analyzing an element having a low melting point and a high ionization potential value by using a surface ionization type mass spectrometer which adopts a normal surface ionization type ionization method.

[0002]

2. Description of the Related Art Mass spectrometry is an analysis method suitable for measuring the abundance ratio of isotopes of elements and minute analysis of inorganic substances. For analysis, it is necessary that the element be ionized.

However, in a usual surface ionization mass spectrometer using filaments of Re, Ta, W, etc., when an element having a relatively low melting point or an element having a relatively high ionization potential value is to be analyzed, it is ionized. Since the element to be analyzed is melted and evaporated as a simple substance by the heating at the previous high temperature, and disappears, such an element cannot be ionized, and therefore, mass spectrometry is impossible.

It is known that ionization is achieved by using iodide or boride as the target element which is difficult to ionize, but it is successful only for a specific element (for example, copper is used). Can be ionized by using copper iodide). Therefore, there has been a strong demand for a method capable of ionizing an element, which is impossible by the conventional method, and easily performing mass analysis with a surface ionization type mass spectrometer.

According to the present invention, when an element is analyzed by a surface ionization type analyzer, the element cannot be ionized because of its low melting point and / or a high ionization potential value. A mass spectrometric method that enables ionization of an element that has been impossible and therefore enables analysis by a surface ionization type mass spectrometer, and is particularly effective for the analysis of low melting point elements such as Zn, Pb, and Sn. The purpose is to provide.

[0006]

In view of the above circumstances, as a result of diligent research conducted by the present inventor, the objective element was contained in the filament in the form of an alloy, a mixture, a coating, etc., and the filament was placed in an oxidizing atmosphere immediately before analysis. The present invention has been completed by finding that it is possible to easily ionize the oxide when it is oxidized by, and as a result, surface ionization mass spectrometry can be performed for the target element. The target element in the present specification is
It is an element to be analyzed.

In order to solve the above-mentioned problems, the invention according to claim 1 replaces the target element provided in the filament with an oxide in an oxidizing atmosphere when performing mass analysis with a surface ionization mass spectrometer. Is a mass spectrometric method, characterized in that the filament comprises a simple substance of a target element of mass spectrometry, an alloy of the target element or a mixture of the target elements, The mass spectrometric method according to claim 1, wherein the filament has a coating made of a simple substance of a target element for mass spectrometry, an alloy of the target element, or a mixture of the target elements.

The present invention will be described in detail below.

The elements to be analyzed in the present invention are:
An element that cannot be ionized by the conventional surface ionization type ionization method due to the low melting point and / or the high ionization potential, or both, can be used without limitation. Specific examples of the element to be analyzed in the present invention include Zn, Pb, Sn, Sb and Ge.

In the method of the present invention, when the element as an analysis target is analyzed by a surface ionization mass spectrometer, the element as an analysis target is changed into an oxide in an oxidizing atmosphere,
Ions of the elements are generated by heating the oxide to a high temperature.

Therefore, in the method of the present invention, it suffices that the element to be analyzed is provided in the filament in a state where it can be converted into an oxide in an oxidizing atmosphere by heating with filament.

As a mode in which the filament is provided with an element to be analyzed, a simple substance of the element to be analyzed,
An aspect in which a filament is formed by an alloy of an element to be analyzed and another element, for example, an alloy of a conventional filament-forming element and a mixture thereof, or the surface of a filament formed of a conventionally known material Part or all of the element is a simple substance of the element to be analyzed, or an alloy of the material forming the conventional filament and the element to be analyzed, or the material forming the conventional filament and the object of analysis The aspect etc. which provide the coating formed with either of the mixture with an element can be mentioned.

Here, the metals conventionally used for filaments are, for example, Re, Ta, W, Ir, R.
h, Pt, Ni, Au, etc. can be mentioned.

When forming an alloy or a mixture of the element to be analyzed and the metal used for the filament, the content of the element to be analyzed is not particularly limited, but is 0.0
01 to 1 At% is preferable, and 0.001 is particularly preferable.
~ 0.1 At%. If it is less than 0.001 At%, the amount of ions generated from the element to be analyzed is small, and detection during analysis may be difficult. Further, if the content of the element to be analyzed is more than 1 At%, workability such as rolling of the alloy or the mixture may deteriorate.

In order to form a filament with either a simple substance or an alloy of the element to be analyzed, a simple substance of the element to be analyzed, or an alloy of the simple substance of the element to be analyzed and another metal is, for example, vacuum melted. Then, after cooling, it may be rolled into a foil shape and then slitted to form a filament having a predetermined shape.

To form a filament from a mixture of a simple substance of an element to be analyzed and another metal, for example, the mixture is formed into a predetermined filament shape and then sintered, or an element and another metal are mixed. The filament can be obtained by, for example, adopting a clad method in which the foil is rolled and adhered.

In order to provide the coating in the above embodiment by using the element to be analyzed, for example, the carrier obtained by using the element to be analyzed, the alloy and the mixture are formed into a predetermined shape, for example, a coating layer, It is formed into pieces, coils, belts, etc., and these are coated on all or part of the surface of the filament. Specifically, forming a coating layer on the entire surface of the filament, the simple substance, alloy or mixture,
Depositing a piece of said element, alloy or mixture so as to cover all or part of the surface of the filament,
The element to be analyzed is used in such a manner that the coil of the single substance, alloy or mixture is wound around the outer periphery of the filament, and the belt formed of the single substance, alloy or mixture is rotated around the filament. The coating in the above aspect can be provided. In short, in the present invention, it is sufficient that a simple substance, an alloy or a mixture of the element can be present on the surface of the filament in any shape so that the oxide of the element to be analyzed can be formed on the surface of the filament. Of. However, good workability, or
Considering that it is possible to firmly bond the element simple substance or the like to the filament so that the element simple substance or the like is not easily peeled off even when the filament is heated, etc. Alternatively, a coating layer of the mixture may be formed on the surface of the filament by plating, vapor deposition, coating or the like.

Next, a method of mass spectrometry using a filament provided with the above element to be analyzed will be described.

A conventionally known surface ionization mass spectrometer can be used as the mass spectrometer.

The filament in the surface ionization mass spectrometer is replaced with the filament containing the element to be analyzed, and the filament is electrically connected to a dedicated lead terminal by spot welding or the like, and is placed at a predetermined position inside the vacuum chamber. To install.

Next, the pressure inside the chamber is 5 × 10 ^-8 h
After evacuating to a Pa or less, allowed to flow into the oxidizing gas by the mass flow meter and adjusted to 10 ^@ 6 to 10 ^over 4 hPa. When the pressure inside the chamber is within the above range,
The element to be analyzed provided in the filament can be gently oxidized to form an oxide of the element well. In contrast, the pressure inside the chamber is ^10-6
It may be less than hPa unable to carry out the oxidation of the object elements sufficiently, sometimes as high as undesirable degradation increases by materials and chamber internal oxidation of the filament than 10 ^{@ 4} hPa. The oxidizing gas may be any gas that can oxidize the element to be analyzed provided in the filament to form its oxide, usually air or oxygen gas is used, and in some cases, A mixed gas of oxygen and an inert gas such as nitrogen, argon or neon may be used.

In this state, the filament is energized to oxidize the target element present on the filament surface. Since the melting point of the formed oxide is higher than the melting point of the elemental element, when raising the filament temperature,
The target element can be heated to the ionization temperature without disappearing due to melting and evaporation. Therefore, the target element can be ionized. That is, it can be analyzed by a surface ionization type mass spectrometer. Ions can be detected by a Faraday cup detector or SEM (secondary electron multiplier).

The above description relates to an example using a surface ionization mass spectrometer. The present invention is not limited to the above example. For example, the surface ionization type mass spectrometer is a separate body, a vacuum chamber, an exhaust device capable of evacuating the inside of the vacuum chamber to a predetermined degree of reduced pressure, a filament attachment device arranged in the vacuum chamber,
An energizing device capable of supplying a predetermined current to the filament attached to the filament attachment device, a gas introducing device capable of introducing a predetermined oxidizing gas into the vacuum chamber, and an ion generated in the vacuum chamber. An oxidizer assembled with an ion derivation device that can be introduced into an analyzer such as a surface ionization mass spectrometer or a quadrupole mass spectrometer may be used.

Next, the method of the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a schematic view showing an example of an apparatus which can be used for carrying out the present invention.

The vacuum chamber 1 has a pump 2 for exhausting gas.
An air introduction pipe 4 is connected to introduce air or oxygen from the mass flow meter 3. The exhaust pump 2 may be a single pump or a plurality of pumps, and the pumps may be connected to each other as shown in FIG. 1 as long as they can exhaust to a predetermined vacuum level. A commercially available mass flow meter can be used.

In the vacuum chamber, a DC power supply device 5a
A filament holder 6 connected to the filament holder 6 is installed, and the filament 7 containing the target element is connected to this holder and is energized.

In the present invention, in addition to the filament containing the target element, an auxiliary heating filament 8 may be provided as shown in FIG. The auxiliary heating filament is formed only by a filament material that does not contain the target element, and is for performing auxiliary heating during analysis, and is particularly effective for measuring elements such as uranium in which ionization hardly occurs.

In the present invention, in the ion source section A of the mass spectrometer, the ions of the target element ionized by the above method are passed through the analyzing section B whose magnetic field is variable, as shown in FIG. And the like are detected by the detection unit C.

[0030]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples.

(Example) An alloy in which 0.05 At% of zinc was added as a target element to rhenium (Re) as a filament material was prepared by vacuum melting to have a thickness of 0.04 mm.
After the foil was rolled and processed into slits, a filament having a width of 0.7 mm was formed by slitting. This filament was spot-welded to a filament holder to obtain a surface ionizing filament. The filament for surface ionization was installed at a predetermined position in a magazine in a vacuum chamber of a commercially available surface ionization mass spectrometer. As shown in FIG. 1, the cryopump 2a, the turbo molecular pump 2b, and the rotary pump 2c were connected to a vacuum chamber, and the inside of the chamber was evacuated to 2 × 10 ⁻⁸ hPa.

Next, air was introduced into the vacuum chamber through an air introducing tube by a mass flow meter, and the degree of vacuum was lowered to 2 × 10 ^-5 hPa. While maintaining the degree of vacuum, the filament was energized with a DC power source for 2 A for 120 seconds to remove zinc from the filament surface.
O). After the energization is completed, the introduction of air is stopped, and the exhaust pump 2 is used again to adjust the degree of vacuum to 2 × 10 ^-8
Evacuated to hPa.

Next, when the filament was started to be energized again, a current value of 5 A was obtained from the Faraday cup detector.
Zinc ions were detected. As a result of mass spectrometry, the abundance ratio of zinc isotopes is ⁶⁴ Zn: ⁶⁶ Zn: ⁶⁷ Zn: ⁶⁸ Zn: ⁷⁰ Zn.
= 48.89: 27.81: 4.11: 18.57:
It was confirmed to be 0.62.

(Comparative Example) 5 on a rhenium filament
A μg zinc nitric acid solution (concentration 5 μg / μl) was put in place, the liquid was evaporated, and then baking was performed.

The filament thus obtained was placed in the same apparatus as in the example, and was evacuated to a vacuum degree of 1 × 10 ^-8 hPa by three kinds of pumps as in the example. In this comparative example, oxidation was not performed in the slightly oxidizing atmosphere as described in the example, and when energization was started in this state, even if the current value was increased to 5 A, the Faraday cup generated rhenium ions. Only the peak was detected and zinc ion was not detected.

A current value of 5 A corresponds to about 2,200 ° C.,
It is considered that zinc melted at its melting point of 419 ° C., evaporated with increasing temperature thereafter, and disappeared before being ionized.

[0037]

[Effects] According to the present invention, conventionally, an element that cannot be ionized and cannot be analyzed in surface ionization type mass spectrometry due to the relationship between the melting point and ionization potential of the target element and the melting point and ionization potential of the filament. Can be ionized by providing in a filament and oxidizing in a slightly oxidizing atmosphere immediately before analysis, that is, mass spectrometry can be performed. Therefore, for example, it is possible to easily measure the presence of isotopes and the abundance ratio of isotopes of elements that have been difficult or impossible to measure in the past.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the present invention.

FIG. 2 is a conceptual diagram showing an arrangement in a vacuum chamber according to the present invention.

[Explanation of sign]

5b ... power source for auxiliary heating, 9 ... dedicated lead, 1
0 ... Slit, 11 ... Ion beam, 12 ...
·Detector

Claims (2)

[Claims] 1. A mass spectrometric method, wherein in performing mass spectrometric analysis with a surface ionization type mass spectroscope, a target element provided in a filament is replaced with an oxide in an oxidizing atmosphere and then mass spectrometric analysis is performed. 2. The filament comprises a simple substance of a target element for mass spectrometry, an alloy of the desired element or a mixture of the desired elements, or the filament has a simple substance of a desired element for mass spectrometry, an alloy of the desired element or the objective. The mass spectrometric method according to claim 1, further comprising a coating made of a mixture of elements.