Sample vial and vial closure device for use in gas analysis and method of using the same

Abstract

The invention comprises a vial closure device, a sample vial incorporating such a vial closure device, and certain methods of using such a vial and closure device. The vial and closure device are intended to contain a gaseous sample or a headspace gas present above a liquid or solid material, so that the gaseous sample or headspace gas can be conveniently analysed, typically by means of an autosampler connected to an analytical instrument such as a mass spectrometer. Mass spectrometric methods of determining the isotopic composition of hydrogen and oxygen comprised in aqueous samples contained in vials fitted with such closure devices are disclosed. The vial closure device comprises a hollow body member locatable in the mouth of a vial, and a first seal for making a substantially gas-tight seal between the exterior of said hollow body member and said vial. The hollow body member comprises an aperture and an aperture closing means for closing said aperture when required, and a second seal, through which a gas sampling means may be inserted. The aperture closing means is operable to open the aperture by the insertion of a gas sampling means through the second seal and is operable to close the aperture when the gas sampling means is withdrawn.

What is claimed is:  
     
         1 . A vial closure device for closing the mouth of a vial which may contain a gas or vapour to be analyzed by extraction through a gas sampling means connected to an analytical instrument, said vial closure device comprising:—
 a hollow body member locatable in the mouth of a said vial; and  
 b) a first seal for making a substantially gas-tight seal between the exterior of said hollow body member and a said vial;  
 said hollow body member further comprising:—
 a) an aperture through which gas present in a said vial may pass into the interior of said hollow body member;  
 b) aperture closing means for closing said aperture when required; and  
 c) a second seal, through which a said gas sampling means may be inserted into said interior, for allowing a said gas sampling means to enter said interior while maintaining a seal around it;  
 
 characterised in that said aperture closing means is operable to open said aperture by the insertion of a gas sampling means through said second seal and is operable to close said aperture when said gas sampling means is withdrawn.  
 
     
     
         2 . A vial closure device as claimed in  claim 1  wherein said aperture closing means comprises a valve seat and a valve body maintained in contact by means of a spring, and wherein said valve body is displaced from said valve seat to open said aperture by contact with a gas sampling means inserted into said hollow body member.  
     
     
         3 . A vial closure device as claimed in  claim 2  wherein said valve seat and said valve body are so disposed that a gas sampling means may be inserted far enough through said second seal to allow gas to be withdrawn from the interior of said hollow body member without displacing said valve body.  
     
     
         4 . A vial closure device as claimed in  claim 1  wherein said second seal operates to close the interior of said hollow body member in the absence of a gas sampling means to make the interior of said hollow body member substantially gas tight.  
     
     
         5 . A vial closure device as claimed in  claim 4  wherein said second seal comprises a septum.  
     
     
         6 . A vial closure device as claimed in  claim 1  wherein said second seal comprises one or more “O” rings located in grooves on the interior of said hollow body member which seal to a said gas sampling means when it is inserted.  
     
     
         7 . A vial closure device as claimed in  claim 1  wherein the exterior portion of said hollow body member is provided with a flange which overlaps the top of a sample vial when said hollow body member is located in the mouth of that vial, said first seal comprises a rubber or plastic washer disposed between the top of the vial and said flanges and said hollow body member is securable to the vial by a threaded retaining ring passed over said hollow body member and engaged with threads on the exterior of the vial.  
     
     
         8 . A vial closure device as claimed in  claim 1  wherein said first seal comprises a tapered joint which may engage with a tapered socket on a said vial.  
     
     
         9 . A sample vessel which may contain a gas or vapour to be analyzed by extraction through a gas sampling means connected to an analytical instrument, said sample vessel comprising a vial fitted with a closure device as defined in any previous claim.  
     
     
         10 . Apparatus comprising a plurality of sample vials for containing a gaseous sample to be analyzed and fitted with a vial closure device, autosampler means comprising a gas sampling means, and means for aligning each of said sample vials with said gas sampling means to allow a said gaseous sample to be taken from each vial in turn by the insertion of said gas sampling means through said vial closure device into said vial, and means for conveying to an analytical instrument at least some of said sample of gaseous sample so taken; 
 said apparatus being characterised in that each said vial closure device comprises: 
 a) a hollow body member located in the mouth of a said vial; and  
 b) a first seal making a substantially gas-tight seal between the exterior of said hollow body member and said vial;  
 said hollow body member further comprising:—
 a) an aperture through which gas present in a said vial may pass into the interior of said hollow body member;  
 b) aperture closing means for closing said aperture when required; and  
 c) a second seal, through which a said gas sampling means may be inserted into said interior, for allowing a said gas sampling means to enter said interior while maintaining a seal around it;  
 
 wherein said aperture closing means is operable to open said aperture by the insertion of a gas sampling means through said second seal and is operable to close said aperture when said gas sampling means is withdrawn.  
   
     
     
         11 . A method of using a vial closure device as claimed in any of claims  1 - 8 , said method comprising the steps of: 
 a) inserting a gas sampling means into the interior of said hollow body member through said second seal;    b) removing residual gas in said vial and the interior of said hollow body member;    c) introducing through said gas sampling means into said vial an equilibration gas of known isotopic composition;    d) removing said gas sampling means from said interior of said hollow body member and allowing the sample contained in said vial to equilibrate with said equilibration gas;    e) inserting a gas sampling means into the interior of said hollow body member through said second seal;    f) removing residual gas from the interior of said hollow body member through said gas sampling means;    g) sampling headspace gas from the interior of said vial through said gas sampling means;    h) conveying a said sample of headspace gas to an isotopic ratio mass spectrometer and determining its isotopic composition;    i) calculating the isotopic composition of an element comprised in said sample from the change in the isotopic composition of said equilibration gas caused by the equilibration of said equilibration gas with said sample.    
     
     
         12 . A method as claimed in  claim 11  wherein the steps of removing residual gas comprise evacuating the gas through the gas sampling means.  
     
     
         13 . A method as claimed in  claim 11  wherein the steps of removing residual gas comprise purging the space occupied by the gas to be removed with a gas which does not contain the element to be analyzed.  
     
     
         14 . A method as claimed in  claim 13  wherein said gas sampling means comprises a twin-needle device so that gas can be introduced though one needle and extracted through the other.  
     
     
         15 . A method as claimed in  claim 11  wherein during steps a), b), e) and f) said gas sampling means is first inserted to allow gas to be removed from the interior of the hollow body member but not so as to actuate said aperture closing means, and wherein the pressure in the hollow body member is monitored during steps b) and f) to ensure that a leak-tight seal has been made between said gas sampling means and said second seal.