Method and an apparatus for analyzing trace impurities in gases

Abstract

The present invention relates to a method and an apparatus for analyzing trace impurities in gases, which enable to analyze a very small quantity of impurities by only a simple operation, without making the column arrangement or the structure of flow complicated. In the apparatus and the method, when the trace impurities are measured in ppb-sub ppb level by a combined analyzer which is equipped with an atmospheric pressure ionization mass spectrometer to the back of a gas chromatography, a mixed gas of various gases is used as a carrier gas or purified gases added to the gases outflowed from a gas chromatography.

1 . A method for analyzing trace impurities in gases, the method comprising the steps of: 
 separating main components and trace impurities from a sample gas conveyed by a carrier gas by using a gas chromatography;    introducing the gases outflowed from said gas chromatography into an atmospheric pressure ionization mass spectrometer; and    analyzing the trace impurities,    wherein a mixed gas is used as the carrier gas.    
     
     
         2 . A method for analyzing trace impurities in gases, the method comprising the steps of: 
 separating main components and trace impurities from a sample gas conveyed by a carrier gas by using a gas chromatography;    adding purified gas into the gases outflowed from said gas chromatography;    introducing the gases into an atmospheric pressure ionization mass spectrometer; and    analyzing the trace impurities,    wherein a mixed gas is used as at least one of the carrier gas and the purified gas.    
     
     
         3 . A method for analyzing trace impurities in gases according to  claim 1  or  2 , characterized in that the mixed gas is Ar—He mixed gas.  
     
     
         4 . A method for analyzing trace impurities in gases, the method comprising the steps of: 
 separating main components and trace impurities from a sample gas conveyed by a carrier gas by using a gas chromatography;    introducing the gases outflowed from said gas chromatography into an atmospheric pressure ionization mass spectrometer; and    analyzing the trace impurities,    wherein a single component gas is used as the carrier gas, and purified gas, the kind of which is different from the carrier gas, are added to the outflowed gas.    
     
     
         5 . A method according to  claim 4 , characterized in that if said carrier gas is He, the added purified gas is one selected from the group of Ar alone, He—Ar mixed gas, Ar—H 2  mixed gas and Ar—H 2  mixed gas, and if said carrier gas is Ar, the added purified gas is He alone, or He—Ar mixed gas.  
     
     
         6 . A method for analyzing trace impurities in gases, the method comprising the steps of: 
 introducing a sample gas into a gas chromatography using He as a carrier gas;    separating main components and trace impurities from the sample gas;    adding a purified gas of Ar alone or Ar—He mixed gas into the gases outflowed from the gas chromatography;    introducing the gases into an atmospheric pressure ionization mass spectrometer; and    analyzing the trace impurities,    wherein the impurity of H 2  is detected by mass number  41  or  81 , and the impurity of methane is detected by mass number  16 .    
     
     
         7 . A method for analyzing the trace impurities in gases, the method comprising the steps of: 
 introducing a sample gas into a gas chromatography by using He as a carrier gas;    separating main components and trace impurities from the sample gas;    adding a purified gas into the gases outflowed from the gas chromatography;    introducing the gases into an atmospheric pressure ionization mass spectrometer; and    analyzing the trace impurities,    wherein at least two of i) He alone, ii) He—Ar mixed gas, iii) He—H 2  mixed gas and iv) Ar—H 2  mixed gas, are selected, and switchably used as said purified gases.    
     
     
         8 . A method according to one of claims  2 , 3 , 4 , 5 , 6  and  7 , characterized in that the added amount of the purified gases is changed depending on the kind of the outflowed gas.  
     
     
         9 . A apparatus for analyzing the trace impurities in gas, the apparatus comprising 
 a gas chromatography for separating the main component and trace impurities from a sample gas conveyed by a carrier gas;    an atmospheric pressure ionization mass spectrometer connected to the back of the gas chromatography; and    a purified gas adding passage for adding the purified gases into the gas outflowed from the gas chromatography, the purified gases adding passage being installed in a passage between the gas escaping part of the gas chromatography and the gas introduction passage of the atmospheric pressure ionization mass spectrometer,    wherein i) a passage for supplying a purified gas whose kind is the same with the carrier gas, ii) a passage for supplying another purified gas whose kind is different from the carrier gas, and iii) a mixed ratio regulating means for regulating the mixed ratio of both purified gases are installed in the purified gas adding passage.    
     
     
         10 . An apparatus according to  claim 9 , wherein an added amount controlling means for regulating the added amount of the purified gases depending on the kind of the outflowed gas, is installed in the purified gas adding passage.