Radiant energy – Ionic separation or analysis – With sample supply means
Reexamination Certificate
1998-02-09
2001-06-19
Anderson, Bruce C. (Department: 2878)
Radiant energy
Ionic separation or analysis
With sample supply means
C250S42300F
Reexamination Certificate
active
06248998
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a plasma ion source mass spectrometer and a method therefor and, more particularly, to a plasma ion source mass spectrometer for detecting trace elements with a mass filter by ionizing a sample with a plasma ion source, and a method therefor.
BACKGROUND OF THE INVENTION
A plasma ion source mass spectrometer of the prior art is described in Items 22 to 25 of Measurement Series 28 “Plasma Ion Source Mass Spectrometry”, the Spectroscopical Society of Japan, edited by Koji Kawaguchi and Taketoshi Nakahara. In this description, object elements contained in a sample solution are ionized by a plasma, and the resultant ions are extracted through an interface unit into a vacuum so that they may be measured by a mass filter. For extracting the ions produced by the plasma into the mass filter, the interface unit generally uses a conical sampling cone and skimmer cone. This interface unit, especially the sampling cone is required to endure the high temperature of the plasma because it is exposed directly to the plasma whose temperature reaches as high as 5,000 to 6,000° C. For this requirement, the sampling cone is usually made of a material having an excellent thermal conductivity and is sufficiently cooled with cooling water so that it may not melt down.
However, the interface unit is given a role to introduce the object elements contained in the solution sample and ionized by the plasma into the vacuum in the same state as in the plasma. If a portion is cooled with the cooling water to a lower temperature, a molecular ion peak may be formed by the cooling, or the interface unit surface may be coated with insulator and charged up by the molecular ion peak formed. This causes a problem of a drop of sensitivity.
As disclosed in Japanese Patent Laid-Open No. 161335/1995, therefore, the temperature of an orifice formed in the sampling cone of the interface unit is detected by means of an optical temperature sensor, and the high-frequency electric power to be supplied to the cavity for generating the plasma is adjusted so that the temperature of the orifice may not allow recombination of ions.
However, this method of adjusting the high-frequency electric power to be supplied to the cavity changes the condition of the plasma generation, so that the ionizing condition is changed to bring up a problem of the change in the analysis sensitivity.
SUMMARY OF THE INVENTION
An object of the invention is to provide a plasma ion source mass spectrometer capable of controlling the temperature of an interface unit without changing the analysis sensitivity, and a method for the mass spectrometer.
In order to achieve this object, the invention adopts the following constructions.
(1) In order to achieve this object, according to the invention, there is provided a plasma ion source mass spectrometer comprising a plasma ion source for ionizing a sample with a plasma; a mass filter for filtering the mass of the sample ionized by the plasma ion source; and an interface unit having an orifice formed in a cone for introducing the sample ionized by the plasma ion source into the mass filter, wherein the plasma ion source mass spectrometer further comprises first cooling means for cooling a plasma generator of the plasma ion source and a plasma generating power source; and second cooling means independent of the first cooling means for cooling the interface unit by feeding it with a coolant and for raising the temperature of the interface unit by changing the cooling efficiency so as to reduce the influence of the deposition adhering to the interface unit.
(2) In the construction (1), preferably, the second cooling means changes the set temperature of the cooling water acting as the coolant. Thanks to this construction, any further deposition of insulator is prevented by controlling the interface unit to a higher temperature, so that in the plasma ion source mass spectrometer and its method the signal intensity does not lower and stable measurement can be made.
(3) In the construction (1), preferably, the second cooling means changes the flow rate of the coolant. Thanks to this construction, the deposition of insulator is prevented by controlling the interface unit to a higher temperature, so that in the plasma ion source mass spectrometer and its method the signal intensity does not lower and stable measurement can be made.
(4) There is provided a plasma ion source mass spectrometry for analyzing the mass spectrum of a sample ionized by a plasma ion source, by introducing the ionized sample into a mass filter through an interface unit, wherein by using second cooling means independent of first cooling means for cooling a plasma generator of the plasma ion source and a plasma generating power source, the temperature of the interface unit is controlled to not higher than a value at which materials forming the interface unit melt, and to not lower than a value at which the change with time of the signal intensity detected by the mass filter lowers. Thanks to this method and construction, the plasma ion source mass spectrometer and its method can control the temperature of the interface unit without changing the analysis sensitivity, so that the signal intensity does not lower and stable measurement can be performed.
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Okumoto Toyoharu
Owada Akira
Tsukada Masamichi
Anderson Bruce C.
Hitachi , Ltd.
Kenyon & Kenyon
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