Patent Publication Number: US-3879181-A

Title: Gas chromatograph, specimen capsule for use therein and process for gas chromatography

Description:
United States Patent Nakamura et a1.  
 GAS CHROMATOGRAPH. SPECIMEN CAPSULE FOR USE THEREHN AND PROCESS FOR GAS CHROMATOGRAPHY Filed: Mar. 2, 1973 Appl. No.: 337,712  
 Foreign Application Priority Data Mar. 9. 1972 Japan 47-24250 Mar. 9. 1972 Japan 47-24251 May 8. 1972 Japan .1 47-44583 US. Cl 55/197; 55/386 Int. Cl B01d 15/08 Field of Search 55/67. 197. 386  
 References Cited UNITED STATES PATENTS 10/1962 Brcnncr 55/197 X [451 Apr. 22, 1975 3.374607 3/1968 Fisher ct al. 55/67 3.518.059 6/1970 Levy 55/67 X 3.550.429 12/1970 MacMurtric et al 55/197 X 3.719.084 3/1973 Walker 55/197 X Primary ExaminerJohn Adee Attorney, Agent. or Firm-Kurt Kelman 1 1 ABSTRACT A gas chromatograph capable of analyzing high boiling substances is provided which has a valve for switching the flow of carrier gas at each alternation of the analysis period and the preparation period fixed outside a constant temperature oven. For use in this gas chromatograph, there is provided a specimen capsule which has a ferromagnetic metal piece fixed on a cell containing therein a sample to be analyzed. Another form of specimen capsule usable therein has a sample carried in position by a foil or net of ferromagnetic metal. Also provided is a process for gas chro&#39; matography which comprises the steps of placing the said specimen capsule in the vaporizer of the gas chromatograph. vaporizing the sample by means of alternative current induction and conducting necessary analysis on the resultant gases.  
 1 Claim, 8 Drawing Figures Detector PATENTEDAFRZZIHYS Detector FIG.5 FIG.6 FIG 7 GAS CHROMATOGRAPH, SPECIMEN CAPSULE FOR USE THEREIN AND PROCESS FOR GAS CHROMATOGRAPHY BACKGROUND OF THE lNVENTlON:  
  This invention relates to an improved pyrolysis gas chromatograph. specimen capsules for use in said gas chromatograph, and a process for analysis using said specimen capsules.  
  Generally in gas chromatography. a sample to be analyzed is placed in a vaporizer and vaporized by heating or by pyrolysis; the vaporized components are swept by a carrier gas into a column filled with a column packing; the components of the sample vapour are carried through the column at different rates. which are governed by their partition coefficient between gas phase and the stationary phase. They emerge from the end of the column at different times. Their presence in the emerging carrier gas is detected by chemical or physical means.  
  It is desirable that the flow of carrier gas through the column packing should be also continued while the column is not in service. namely during the preparation period, so as to keep the column packing under fixed conditions and protect it against possible degradation. The carrier gas flows in different paths during the analysis period and during the preparation period. The switch of the path of flow is effected by means of a valve which is placed in the piping of the carrier gas. In most gas chromatographs. the column and the vaporizer are encased in a constant temperature oven so as to be kept at a predetermined temperature.  
  In the conventional pyrolysis gas chromatograph, the said switching valve is placed between the vaporizer and the column and, during the analysis period. the vaporized components of the sample are carried by the carrier gas from the vaporizer to the analyzing column via the valve. It is therefore, necessary that the valve be placed inside the constant temperature oven and maintained at the constant temperature, so that the sample is prevented from being condensed while passing through the valve.  
  The switching valve. is required to incorporate compressible packings of a rubbery material which serve the purpose of sealing. To satisfy the purpose, these parts are made of heatproof plastics such as, for example. Teflon. Even Teflon that has properties most suited to the purpose cannot withstand temperatures higher than 170C. Thus. the temperature at which the constant temperature oven maintains the analyzing column is limited to the highest temperature that the aforementioned parts can withstand.  
  As concerns the injection of a sample into the vapor izer of the gas chromatograph, one known method accomplishes the injection by taking the sample in a micro-syringe. piercing the needle of this syringe through a rubber septum placed to close the entrance to the vaporizer and injecting the sample into the vaporizer.  
  when this method is applied to analyzing a volatile substance mingled with an involatile substance such as, for example, a solvent in a paint. the vaporization of the volatile component occurs first and requires a considerable length of time. Consequently, the sample tends to disperse prior to arrival at the column or it is found to be quite difficult to inject the entire sample to the column. There is another disadvantage that the residue of the sample cannot be extracted after completion of the analysis and it is left to contaminate, the vaporizer and the column.  
  In other methods. the sample is injected into the vaporizer and thermally decomposed therein by the action of heat. There is known. for example. a method comprising the steps of having a sample solution deposited on the surface of a ferromagnetic metal wire about 0.6 mm in diameter and about 20 mm in length, drying the solution, inserting the wire into the vaporizer. exposing the wire to alternative current magnetic field thereby inducing it to radiate heat thereby pyrolyzing the sample deposited on the wire. Since this method requires the sample to be deposited on the surface of the wire. the applicability of this method is limited to liquid samples or to solid samples which can be dissolved with solvents into solutions. The method is not applicable to solid insoluble samples. When a given solid sample is converted into a liquid sample by the use of a suitable solvent. the liquid sample is deposited on the wire and subsequently dried free of the solvent. From the practical point of view. however. thorough removal of the solvent content from the deposited sample is an impossibility. The gas produced from the deposited sample by pyrolysis. therefore, entrains the solvent component. This means that the chromatogram obtained by this method does not represent accurate analysis of the solid sample in the form thoroughly free from foreign matter.  
  The amount of the sample solution which is deposited on the wire must also be considered. Even if the solution to be deposited is the same, it is impossible to have exactly the same amount of solution deposited on all the wires in use. In the case of an excess of deposit. the recording of the results of analysis becomes impracticable because the peaks protrude over the edge of the chart paper. One same solution is deposited on a plurality of wires and the results of analysis conducted on each wire are recorded. therefore, there is involved the troublesome work of making proper adjustment on each wire so that the peaks do not protrude over the edge of the chart paper. The amount of sample thus deposited on the wire is quite small. In the case of an operation in which mass spectrum is simultaneously performed using a mass spectrometer connected next to the gas chromatograph, therefore. the amount of the sample on the wire is not sufficient, making it impossible to carry out the mass spectrometric identification.  
  It is a primary object of this invention to provide a gas chromatograph adapted so that the path for forwarding the vaporized components of samples produced by pyrolysis can be elevated to high temperatures without reference to the packing and other similar material used in the switching valve.  
  It is another object of this invention to provide a specimen capsule for use in gas chromatograph, which permits accurate analysis of the volatile substances contained in high boiling substances and further provide a process for analysis using the said specimen capsale.  
  It is still another object of the present invention to provide a specimen capsule for pyrolysis which eliminates the necessity of a solvent even where the sample to be analyzed happens to be a solid substance and which is also usable where the sample is a liquid substance and further to provide a process for the analysis using said specimen capsule.  
  Yet another object of this invention resides in providing a specimen containing a constant amount of sample.  
 SUMMARY OF THE INVENTION This invention relates to a gas chromatograph which enables any high boiling substance to be analyzed as desired. In the conventional gas chromatograph. the valve designed for switching the path of the flow of carrier gas at each alternation of the analysis period and the preparation period is positioned midway between the vaporizer and the column and is enclosed in the constant temperature oven. The gas chromatograph according to this invention has this switching valve disposed outside the constant temperature oven in front of the vaporizer so that the vaporized sample will not flow through this valve. This invention also relates to a specimen capsule for use in this gas chromatograph and to a process for the analysis using said specimen capsule.  
  To be specific, in one embodiment of the specimen capsule, a cell made of galss or a substance with a relatively low melting point such as high molecular substance is fitted with a piece of ferromagnetic metal at one part thereof so that the test specimen is prepared by placing a given sample in this cell. Then, the prepared specimen is inserted into the vaporizer of the gas chromatograph. On exposure to alternative current induction. the ferromagnetic metal piece is elevated in temperature to the point of breaking the cell, with the result that the components which have been vaporized out of the sample by this time are swept by the carrier gas into the column and are subjected to determination.  
  In another embodiment, a foil or net made of the said ferromagnetic metal is used to contain the sample directly. A capsule is formed of a foil of the ferromagnetic metal and the specimen is prepared by placing therein a liquid or solid sample. The specimen thus prepared is then inserted in the vaporizer of the gas chromatograph and exposed to alternative current induction so that the ferromagnetic metal is heated to the extent of radiating heat and causing pyrolysis of the sample into a gaseous state. The gases thus produced from the sample are forwarded by the carrier gas into the column, wherein it is subjected to determination.  
  Other objects and characteristics of the present invention will become apparent from the consideration of the further description of the invention to be given in detail hereinafter with reference to the accompanying drawings.  
 BRIEF EXPLANATION OF THE DRAWING I and nets made of ferromagnetic metal.  
 DETAILED DESCRIPTION OF THE INVENTION The gas chromatograph of this invention will be explained with reference to FIG. 1.  
  In the diagram, 1 denotes a constant temperature oven, 2 a vaporizer disposed within the constant temperature oven and intended to vaporize or pyrolyze a sample and 3 an analyzing column and disposed inside the said oven 1 next to the said heater compartment, i.e. vaporizer 2.  
  The vaporizer may be a quarts tube, for example, which has an opening to the outside of the constant temperature oven. The said opening is kept closed at all times during operation with a septum 13. The septum 13 is removed when the specimen is inserted, when the interior of the vaporizer is cleaned or when the system is being prepared for analysis operation.  
  In the present invention, a pipe 4 for forwarding the carrier gas to the vaporizer 2 is provided outside the constant temperature oven wiht a switching valve 5. A pipe 6 for forwarding the carrier gas containing the separated components of the sample from the column 3 to a detector is provided inside the constant temperature oven 1 with a tee coupling 7. The aforesaid valve 5 and this tee coupling 7 are connected to each other by a pipe 8 which runs parallel to the vaporizer 2 and the column 3. Said vaporizer 2 is exposed to an alternative current magnetic induction field generated by oscillator 10. The said pipe 8 is provided inside the constant temperature oven 1 with a dummy column 9 which is designed to balance the flow rate resistance.  
  The said dummy column 9 is formed so as to provide the same amount of resistance to the passage of gas as the column 3. Consequently, possible difference in the volume of carrier gas being forwarded is minimized when the gas is flowing through the column and when it is flowing through this dummy column. This enhances the stability of operation of the entire system. The switching valve 5 has a structure of the so-called three-way valve in which the path for the gas is shaped like the letter T. The forked coupling 7 has the structure of a T-shaped pipe.  
  The gases which may be used as the carrier gas in this invention are N He, etc.  
  The manner in which the switching valve 5 in the system of this invention is actually operated will be described in detail.  
  The valve 5 is a three-way valve of the kind frequently found in common use. FIG. 1 illustrates the valve 5 in the state which it assumes while the system is in the preparation period. During the preparation period, the carrier gas flows from the valve 5 to the tee coupling 7 via the pipe 8 which contains the dummy column 9. The flow of carrier gas is divided by the tee coupling 7 into two flows, one to the vaporizer 2 and the other to the concentration detector. By this flow of carrier gas, the column 9 has its column packing protected against possible degradation.  
  When the operation is to be switched to the analysis period, the three-way valve 5 is switched so that the carrier gas will flow through the pipe 4 and the flow of the gas to the pipe 8 will be stopped. Consequently, the  
 carrier gas flows through the vaporizer 2 and enters thecolumn 3 while entraining the vaporized components of the sample. In the column, the components are separated from one another by the column packing. Then, they are forwarded sequentially from this column and swept to the concentration detector.  
  An auxiliary piping containing a reference column 11 within the constant temperature oven is incorporated in the present gas chromatograph for the purpose of maintaining the accuracy of analysis at a high level.  
  In the gas chromatograph of the present invention. the switching valve 5 is positoned in front of the vaporizer 2 and outside the constant temperature oven as already described. The vaporized sample is not allowed to pass through this valve under any condition. Therefore. the sample can be heated to as high a temperature as desired without reference to the kind of material of which the valve or its interior parts are made.  
  Owing to this innovation. the present invention has made possible the application of the technique of gas chromatograph to substances with high boiling points.  
  An explanation will now be given of the specimen capsule of this invention which permits accurate analysis selectively of the volatile substances in a mixture with involatile substances and to a process for analysis using the said specimen capsule.  
  FIG. 2, FIG. 3 and FIG. 4 illustrate preferred embodiments of the specimen capsule of the present invention. Referring to FIG. 2. l4 denotes a cell made of glass or a polymer of a high molecular substance and IS a piece made of a ferromagnetic metal and pierced through the bottom of the said cell to complete the specimen cap sule. A given sample 16 is poured through the hole 17 into this specimen capsule and the hole is sealed to form the specimen.  
  FIG. 3 showns a specimen formed by charging the sample 16 into a specimen capsule having cell 14 made of glass or some other high molecular material. inserting the piece 18 of ferromagnetic metal through the hole and finally sealing the hole. The specimen capsule shown in FIG. 4 is formed by winding a wire 19 of ferromagnetic metal in the shape of a coil or ring around the cell I4 made of glass or some high molecular material after the sample 16 has been charged in the cell and the hole sealed.  
  The specimen capsules described above are invariably prepared by forming cells of glass or some high molecular material. hermetically containing given samples in the cells. and attaching pieces of ferromagnetic metal to one part of such cells. As a matter of course, the shapes of the specimen capsules and those of the pieces of ferromagnetic metal are not limited to those of the illustrated embodiments. The high molecular substance of which the cell is made is desirably such that it will not produce any complicated pyrolysis product. Examples of high molecular substances satisfying this requirement are polystyrene, polyethylene, polypropylene and polymethylmetaacrylate. Now a description will be given of a process for analysis using the specimen capsules of this invention. The specimen capsule described above is inserted into the vaporizer and held there until the volatile components of the sample are completely gasified. Thereafter the specimen cap sule is exposed to alternative current induction. Consequently. the ferromagnetic metal is elevated in temperature and reaches Curie point temperature. Because of the heat, the cell of glass or high molecular material held in contact with the ferromagnetic metal is broken or fused, with the result that the vaporized components of the sample contained in the cell are all at once released into the vaporizer. The involatile components of the sample held within the cell are not in the least allowed to leak out of the system. The components which have thus been released in the vaporizer are carried by the carrier gas into the column and subsequently swept into the detector for desired determination. The Curie temperature is 770C for iron. 358C for nickel and 596C for an alloy consisting of 60% of nickel and 40% of iron. for example. The ferromagnetic metal for the specimen capsule may be selected from among the metals and alloys just mentioned plus nickel-iron alloys, nickelcobalt alloys and other ferromagnetic alloys.  
  The process of analysis by this invention utilizing the specimen capsule of this invention has an advantage that all the volatile components of the sample are thoroughly volatilized and subjected to analysis and the residue of the sample can be removed from within the vaporizer after completion of the analysis. Another advantage of the present process is that the residue from the volatilization continues to remain within the cell and, therefore. finds no opportunity to smear the interior of the vaporizer or the column.  
  An explanation will now be given of a specimen capsule for use in gas chromatograph. which is suited for pyrolysis by alternative current induction heating of samples with high boiling points such as. for example high molecular substances. and particularly solid substances resistant to all solvents. and also to a process for the analysis using aid specimen.  
  FIG. 5, FIG. 6, FIG. 7 and FIG. 8 are preferred embodiments of specimen capsules of the present invention. Referring to FIG. 5, 20 denotes a foil of ferromagnetic metal having a very small thickness of the order of 0.05 mm and 21 a sample which is wrapped in the said foil. In this case. the sample is a solid substance.  
  In FIG. 6, a specimen capsule 22 is formed of a foil offerromagnetic metal. This specimen capsule is suited for the analysis of a liquid sample. It can. of course, be applied to analysis of a solid sample.  
  FIG. 7 and FIG. 8 show samples 25 and 26 wrapped in foils 23 and 24 respectively. In the case of these two embodiments, the samples are limited to solid substances. The foils of ferromagnetic metal described in the above specimen capsules may be replaced by thin nets made of ferromagnetic metal. These nets, however, are not suitable for analysis of liquid samples.  
  Further. the specimen capsules may be prepared in structures combining foils and nets of ferromagnetic metal. A specimen capsule may be formed. for example, by placing a given sample on a foil of ferromagnetic metal and then covering the sample with a net.  
  FIG. 5, FIG. 6, FIG. 7 and FIG. 8 merely show a few preferred embodiments of the specimen capsules of the present invention. The specimen capsules according to this invention are not limited to the shapes illustrated therein. Examples of other shapes the specimen capsules of this invention may assume include those formed by wrapping a foil of ferromagnetic metal around a given sample. by enclosing a sample with a net of ferromagnetic metal. by bending a foil or net mentioned above and inserting a sample inside the fold, and by placing a sample on a foil or net produced in the shape of a plate.  
  When any of the specimen capsules described above is mounted in the vaporizer of the gas chromatograph and then exposed to alternative current induction, the ferromagnetic metal piece is inductively heated and the sample is pyrolyzed into gaseous components, which are dispersed throughout the interior of the vaporizer. By a known method previously described, the gases are swept by the carrier gas to the column. The components of the sample vapour are carried through the column at different rates, which are governed by their par tition coefficient between gas phase and the stationary phase. They emerge from the end of the column at different times. Their presence in the emerging carrier gas is detected by chemical or physical means. As the ferromagnetic metal used in the specimen capsule of this type, iron, nickel. nickel-iron alloys nicke]cobalt alloys. etc. may be used as already described in earlier sections dealing with the specimen capsules for use in the analysis of volatile samples and the process for analysis using such specimen capsules. Satisfactory selection has only to take into account the suitability to the kind of sample to be analyzed.  
  The specimen capsules and the process of analysis according to the present invention can use a solid sam&#39; ple in its unaltered form for the purpose of analysis and, therefore dispense with the treatment of dissolving a solid sample in a solvent which is indispensable for the conventionally known alternative current induction heating technique. Further, this invention has a great merit of permitting very easy preparation of specimen capsules containing required sample. addition to a decided advantage that it can be employed for the analysis of liquid samples.  
 We claim:  
 1. A gas chromatograph comprising in combination:  
 A. a constant temperature oven;  
 B. a carrier gas introducing pipe;  
 C. a vaporizer having an entrance for sending a sample thereinto to which said carrier gas introducing pipe is connected within said constant temperature oven for vaporizing said sample and for mixing the resultant vapor with the carrier gas introduced from said introducing pipe and means for discharging the mixed gas out of said vaporizer;  
 D. an analyzing column disposed inside said constant temperature oven next to said vaporizer and having a column packing therein for receiving mixed gas discharged from said vaporizer. separating the sample into components by means of said column packing and means for sending said components outside said analyzing column one after another;  
 E. a tee coupling disposed inside said constant temperature oven next to said analyzing column;  
 F. a three-way valve disposed at said carrier gas introducing pipe and outside said constant temperature oven, said three-way valve having an entrance for receiving carrier gas and two exits, one for sending the carrier gas in the direction of said vaporizer and the other for sending the carrier gas in another direction; and capable of being switched in either di&#39; rection;  
 G. a system having a dummy column within said constant temperature oven by which said tee coupling and three-way valve are connected with each other:  
 H. a detector disposed outside said constant temperature oven to which said tee coupling is connected for detecting the components sent from said analyzing column; and  
 l. a system having a reference column within said constant temperature oven.  
  l l l l