Method and apparatus for the introduction of a vaporizable sample into an analytical test apparatus
This is a continuation-in-part of U.S. patent application Ser. No. 824,248, filed Jan. 30, 1986, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     Methods for introducing samples into an apparatus for the analysis of vapors and vapor-entrained materials, such as gas chromatographs and ion mobility spectrometers, have hitherto been (1) mainly limited to handling liquids, for example, a syringe carrying a liquid sample is introduced into many conventional gas chromatographs through a rubber septum, or (2) of the type that allows vapor-entrained samples to be introduced from sample tubes. However, the sample introduction means used in these methods must be designed specifically for the particular purpose of analysis. An example of this type of means is the Perkin Elmer Model ATD 50™ system, two-stage adsorber type gas chromatograph in which a sample is adsorbed onto an adsorbent material such as para-polyphenylene-oxide in the form of TENAX™ contained in a sample tube and then the sample is transferred to an adsorbent material in a second sample tube of different (usually smaller) dimensions from those of the first sample tube. A particular variant of this procedure is described by F. Raschdorf in Chimia 32, 1978. Raschdorf employs a needle method for the introduction of compounds into gas chromatographs. A 100 ml gas syringe is described by Raschdorf and is employed to draw a known volume of sample gas through a thick needle containing an adsorbent such as TENAX. This needle, which functions as a sample tube, is disconnected from the barrel of the syringe and then connected to a supply of carrier gas before being introduced into the gas chromatograph. While the needle of Raschdorf is useful, there are drawbacks in that (a) it requires a large barrelled syringe and adsorbent loaded needle as opposed to the more convenient and conventional sample tubes, (b) a carrier gas entrained sample flow rate of 14 cc/min, which is required to transfer the sample from the syringe to the gas chromatograph, is an order of magnitude too great to be handled by capillary chromatography columns of the type preferred for microanalysis, and (c) hardware modifications may be necessary in the sample introduction port of the chromatograph to accommodate the large needle that is used. 
     There is a need for a method and an apparatus for the introduction of a vaporizable sample into an analytical test apparatus which uses sample tubes of the conventional type, with the attendant advantages of choice of adsorption material that they allow, but which is also capable of matching the ideal flow for proper desorption through conventional sample tubes of about 30 cc/min., with the optimum flow for capillary gas chromatograph operations of 1-5 cc/min. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided an apparatus for the introduction of a vaporizable sample into an analytical test apparatus, comprising: 
     a sample tube having an interior for the collection of a vaporizable sample and from which, when heated, the sample may be vaporized, 
     means at an upstream end of the sample tube for passing a carrier gas to the sample tube interior for elution therefrom of the sample in vapor form; 
     a hypodermic syringe having a heat dissipating metal walled, hollow needle for the condensation of eluted sample, from the sample tube on an inner surface of the needle, and transfer of sample from the inner surface in a revaporized, concentrated form to the analytical test apparatus; 
     a valve attached to the hypodermic syringe, at a position adjacent the needle, for venting carrier gas therefrom from which vaporized sample has been condensed in the needle; and 
     a plug closing the downstream end of the sample tube and, in operation, sealing said needle in a perforation for the transfer of the eluted sample from the sample tube to the hypodermic syringe. The apparatus may include heating means for heating the sample tube. 
     The sample tube may contain sample adsorbent material, such as, for example, a polymeric sample-adsorbent material based on the monomer 2,6-diphenyl-p-phenylene oxide e.g. TENAX-GC™ or material such as platinum gauze, for the entrapment of sample vapors. 
     The syringe may comprise a barrel and a plunger. The valve for venting the hypodermic syringe may be in the side of the barrel thereof and comprise a pipe containing a closable valve. 
     The apparatus according to the present invention may be used in combination with cooling means for cooling at least a part of the metal walled, hollow needle. The apparatus according to the present invention may also be used in combination with a carousel for introducing and removing successive sample tubes for the withdrawal of a sample therefrom into the hollow needle with automatic means for the introduction of the hollow metallic needle into the analytical test apparatus. 
     Further according to the present invention there is provided a method for the introduction of a vaporized sample into an analytical test apparatus, comprising: 
     (a) collecting said sample in a condensed form in a sample tube; 
     (b) closing a downstream end of the sample tube with a plug; 
     (c) inserting a heat dissipating metal walled needle of a hypodermic syringe through the plug; 
     (d) heating said sample in the tube to render the sample in vapor form; 
     (e) feeding a carrier gas through the tube to entrain vaporized sample and transport it into the needle; 
     (f) condensing the sample from the carrier gas onto the inner surface of the needle; 
     (g) venting carrier gas from which the sample has been condensed, from the hypodermic syringe at a position adjacent the needle, whereby 
     (h) said needle may be introduced into a heated sample intake port of the analytical apparatus, for injection of the sample in a revaporized, concentrated form therein for analysis. 
     The method according to the present invention may be used with a capillary gas chromatograph or an ion mobility spectrometer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings which illustrate, by way of example, an embodiment of the present invention, FIGS. 1 and 2 are partly sectional side views of an apparatus for the introduction of a vaporizable sample into an analytical test apparatus. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, there is shown a sample tube 1 containing platinum gauze 3, which may be placed in heater 2, and connected at an upstream end via a TEFLON™ type polytetrafluorethylene pressure plate 4 to a source of carrier gas 5. At the downstream end of sample tube 1 there is shown a TEFLON plug 6 perforated in sealing engagement by a heat dissipating metal walled, hollow needle 7, said needle 7 forming part of a hypodermic syringe 8 with barrel 9 and plunger 10. A one-way valve 11, connected to a vent 12, is set in the side of barrel 9. 
     In FIG. 2, similar parts to those shown in FIG. 1 are designated by the same reference numerals and the previous description is relied upon to describe them. 
     In FIG. 2, there is shown chain dotted the outline of a capillary gas chromatograph 14 having a heated injector port generally designated 15. The heated injector port has a heat conductive metal block 16 provided with a passageway 18 lined with a tubular lining 20, a recess 22 containing a heater 24, and a recess 26 containing a thermocouple 28. 
     The lining 20 protrudes from the block 16 and has a polytetrafluoroethylene septum 30 and a screw threaded cap 32 sealing the end thereof. The cap 32 has an inwardly tapering needle entry port 34. 
     The block 16 and the lining 20 have a carrier gas inlet 36. 
     A partition tube 38 extends along the lining 20 and is spaced from the septum 30. 
     This embodiment is preferably operated as follows. Sample tube 1 is exposed to a source (not shown) of vaporized sample which is deposited in a condensed form upon the platinum gauze 3. The sample tube 1 is then connected to a source of carrier gas (not shown) by means of a pipe 5 and a TEFLON pressure plate 4. A TEFLON plug 6 is then inserted in the other end of sample tube 1 in a vapor tight manner, the needle 7 is inserted in the plug 6 as illustrated in FIG. 1, and then the one way valve 11 is opened. The heater 2, which may be an aluminum heating block, is then used to heat the sample tube 1 and vaporize the sample. A valve (not shown) controlling the supply of carrier gas to pipe 5 is opened so that the carrier gas and vaporized sample are carried into the needle 7 at a flow rate which is preferably about 30 cc/min, where the sample is condensed and collected on the inner surface of the needle, while the carrier gas is vented through the one-way valve 11 to the vent 12. With the one-way valve of the syringe 8 closed, the needle containing the condensed sample is withdrawn from plug 6 and as shown in FIG. 2 is introduced into the heated injector port 15 of the gas chromatograph 14 by piercing the septum with the needle 7. Carrier gas is passed along the passage 36, along the outside of the partition tube 38 towards the septum 30 where, as shown by the arrows, it enters the partition tube 38 into the separation column (not shown) of the gas chromatograph 14. The condensed sample in the needle 7 vaporizes rapidly on the introduction of needle 7 into the heated injector port 15 of the analytical apparatus. The plunger 10 is then depressed as shown in FIG. 2 to drive the sample vapors from the needle 7 into the carrier gas stream to be entrained therein and conveyed to the separation column of the gas chromatograph 14, typically flowing at a rate of 1-5 cc/min. 
     If desired, a carousel of the sample tubes may be used, each capped with a TEFLON or rubber plug 6, and provision made for a stream of carrier gas to transfer vaporized samples from successive tubes 1 to the needle 7 of the hypodermic syringe 8. The syringe 8 may be activated by a servo-mechanism to inject successive samples into the heated injector port of the analytical apparatus. 
     Desirable features of the present invention are (a) conventional sample tubes may be used; (b) laminar flow rate during ejection of the vaporized sample from the needle allows the apparatus to be used with capillary gas chromatographs; (c) the needle may be significantly smaller than needles of the type employed in known apparatus; (d) the needle does not require an adsorbent packing which is used in known apparatus; and (e) no modifications to the analytical apparatus (e.g. gas chromatograph, ion mobility spectrometer) are necessary. 
     Mixtures of chlorinated biphenyls have been extracted from an air stream into a sample tube of the type shown in FIG. 1. The samples were then transferred to syringe needles and these used to transfer the samples into suitable analytical test apparatus such as a capillary gas chromatograph or ion mobility spectrometer, in the manner described with reference to FIGS. 1 and 2. 
     Using the apparatus of the type described with reference to FIGS. 1 and 2, very satisfactory chromatographic results have been obtained. The apparatus can yield excellent peak sharpness and reproducibility. Given below are some results for six compounds tested using the apparatus shown in FIGS. 1 and 2. 
     
                                           EXAMPLE 1                               
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        Amount                                                            
        of Sample                                                         
               Heating Time   Gas Flow            Type of                 
        Collected On                                                      
               (applied to                                                
                       Heating                                            
                              Through                                     
                                    Gas Chromatograph                     
                                                  G.C.                    
Compound                                                                  
        Needle adsorber)                                                  
                       Temperature                                        
                              Adsorber                                    
                                    Conditions For Analysis               
                                                  Detector                
                                                         Comments         
__________________________________________________________________________
Diphenylamine                                                             
        2      2 min   250° C.                                     
                              Helium                                      
                                    Column is DB-1fused                   
                                                  nitrogen                
                                                         needle           
        nanograms             20 psi                                      
                                    silica, 15 m long,                    
                                                  phosphorous             
                                                         kept at          
        (19.sup.-9 g)         15 cc/min                                   
                                    0.32 mm I.D.  detector                
                                                         room temp.       
                                    Injector Temp. 250° C.         
                                                  (NPD)                   
                                    Oven Temp. T.sub.o = 60° C.    
                                    Hold Time: 30 sec.                    
                                    Ramp Rate: (60° C. to          
                                    130° C. at 6° C./Min)   
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                                           EXAMPLE 2                               
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       Amount                                                             
       of Sample                                                          
              Heating Time   Gas Flow           Type of                   
       Collected On                                                       
              (applied to                                                 
                     Heating Through                                      
                                   Gas Chromatograph                      
                                                G.C.                      
Compound                                                                  
       Needle adsorber)                                                   
                     Temperature                                          
                             Adsorber                                     
                                   Conditions For Analysis                
                                                Detector                  
                                                       Comments           
__________________________________________________________________________
2-methyl-                                                                 
       10     11/2 min                                                    
                     250° C.                                       
                             Helium                                       
                                   As example 1 except                    
                                                nitrogen                  
                                                       needle             
aniline                                                                   
       nanograms             20 psi                                       
                                   for:         phosphorous               
                                                       kept at 0°  
                                                       C. to              
       (10.sup.-9 g)         15 cc/min                                    
                                   Oven temp. T.sub.o = 60°        
                                                detector                  
                                                       improve            
                                   Hold Time: 30 sec.  condensation       
                                   Ramp Rate: 60° C.               
                                   130° C. at 6° C.         
__________________________________________________________________________
 
    
     
                                           EXAMPLE 3                               
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       Amount                                                             
       of Sample                                                          
              Heating Time   Gas Flow           Type of                   
       Collected On                                                       
              (applied to                                                 
                      Heating                                             
                             Through                                      
                                    Gas Chromatograph                     
                                                G.C.                      
Compound                                                                  
       Needle adsorber)                                                   
                      Temperature                                         
                             Adsorber                                     
                                    Conditions For Analysis               
                                                Detector                  
                                                        Comments          
__________________________________________________________________________
cocaine                                                                   
       10     21/2 min                                                    
                      250° C.                                      
                             Nitrogen                                     
                                    As example 1 except                   
                                                nitrogen                  
                                                        needle            
       nanograms             20 psi for:        phosphorous               
                                                        kept at           
       (10.sup.-9 g)         20 cc/min                                    
                                    Oven temp. T.sub.o = 60°       
                                                detector                  
                                                        room              
                                    Hold Time: 1 min    temperature       
                                    Ramp Rate: 60° C. to           
                                    150° C. at 20° C./min   
                                    150° C. to 200° C. at   
                                    6° C./min.                     
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                                           EXAMPLE 4                               
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       Amount                                                             
       of Sample                                                          
               Heating Time   Gas Flow             Type of                
       Collected On                                                       
               (applied to                                                
                      Heating Through                                     
                                    Gas Chromatograph                     
                                                   G.C.                   
Compound                                                                  
       Needle  adsorber)                                                  
                      Temperature                                         
                              Adsorber                                    
                                    Conditions For Analysis               
                                                   Detector               
                                                        Comments          
__________________________________________________________________________
silvex [ ™]                                                            
       50      45 sec 250° C.                                      
                              Nitrogen                                    
                                    Column is SE-S4                       
                                                   Electron               
                                                        needle            
methylester                                                               
       picograms              20 psi                                      
                                    capillary fused silica                
                                                   Capture                
                                                        kept at           
       (10.sup.-12 g)         25 cc/min                                   
                                    15 mm long × 0.25 mm            
                                                   Detector               
                                                        room              
                                    Injector Temp. 225° C.         
                                                   (ECD)                  
                                                        temperature       
                                    Detector Temp. 350° C.         
                                    Oven Temp. T.sub.o = 100° C.   
                                    Hold Time = 1 min                     
                                    Ramp rate: 100° C. to          
                                    150° C. at 20° C. to    
                                    150° C. to 200° C. at   
                                    5°  C./min                     
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                                           EXAMPLE 5                               
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       Amount                                                             
       of Sample                                                          
              Heating Time  Gas Flow          Type of                     
       Collected On                                                       
              (applied to                                                 
                     Heating                                              
                            Through                                       
                                  Gas Chromatograph                       
                                              G.C.                        
Compound                                                                  
       Needle adsorber)                                                   
                     Temperature                                          
                            Adsorber                                      
                                  Conditions For Analysis                 
                                              Detector                    
                                                   Comments               
__________________________________________________________________________
Aldrin [ ™]                                                            
       200    45 sec 250° C.                                       
                            Nitrogen                                      
                                  As example 4                            
                                              Electron                    
                                                   needle                 
       picograms            10 psi            Capture                     
                                                   kept at                
       (10.sup.-12 g)       20 cc/min         Detector                    
                                                   room                   
                                              (ECD)                       
                                                   temperature            
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                                           EXAMPLE 6                               
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Analysis of Heroin using an ion mobility spectrometer                     
      Operating Conditions                                                
                       Drift tube and                                     
      Carrier gas      injection port                                     
                                    Electric field                        
                                           Gate Drift                     
Compound                                                                  
      flow rate  Drift gas                                                
                       temperature                                        
                               Pressure                                   
                                    gradient                              
                                           Width                          
                                                Length                    
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Heroin                                                                    
      400 cc/min 660 cc/min                                               
                       220° C.                                     
                               752 Torr                                   
                                    214 V/cm                              
                                           0.2 msec                       
                                                8 cm                      
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 Signal averaging using Nicolet model 5351-04 [ ™] signal averager     
 Heroin gave two ion peaks with drift times of 17.9 and 19.6 msec.        
 Reduced mobility values of the two peaks (K.sub.o) are 1.14 amd 1.04     
 cm.sup.2 volt.sup.-1 sec.sup.-1 respectively.                            
 
    
     It should be noted that the carrier gas flow through the sample tube 1, when transferring the sample from a sample tube 1 to the needle 7, was found to be of the order of 15-25 cc/min while the gas flow for conveying the vaporized sample from the needle 7 to the gas chromatograph was found to be of the order of 1-1.5 cc/min. From this it will be seen that condensing the vaporized sample in the needle and exhausting carrier gas from the syringe has the effect of delivering a much higher concentration of the sample in the carrier gas that is delivered to the gas chromatograph. For low boiling point compounds such as 2-dimethylaniline (Example 2) the needle should preferably be cooled to below ambient temperatures to improve condensation of the condensed sample in the needle 7. The apparatus according to the present invention has proved particularly useful in the analysis of polychlorinated biphenyls. 
     In some embodiments of the present invention the inner surface of the needle may comprise a sorbent material for the sample, such as, for example, a silicone coating applied directly to the inner surface of the metal wall, or to a glass capillary lining for the metal wall.