|Publication number||US2991647 A|
|Publication date||Jul 11, 1961|
|Filing date||Jul 12, 1957|
|Priority date||Jul 12, 1957|
|Publication number||US 2991647 A, US 2991647A, US-A-2991647, US2991647 A, US2991647A|
|Inventors||Joseph Harris Rano|
|Original Assignee||Prec Instr Company|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Referenced by (23), Classifications (8)|
|External Links: USPTO, USPTO Assignment, Espacenet|
July 11, 1961 Filed July 12, 1957 CARRIER GAS & 1
R. J. HARRIS CHROMATOGRAPHY 4 Sheets-Sheet 1 DETECTOR- HEATED CHAMBER CHROMATOGRAPHIC COLUMN FIGURE I SAMPLE INLET SYST E CARRIER GAS Rono J. Harris Inventor R. J. HARRIS CHROMATOGRAPHY July 11, 1961 4 Sheets$heet 2 Filed July 12, 1957 Runo J. Harris Inventor 4 Sheets-Sheet 3 R. J. HARRIS CHROMATOGRAPHY Mm mm 1% 511 I r 2 H mmDwE July 11, 1961 Filed July 12, 1957 Runo J. Harris Inventor July 11, 1961 R. J. HARRIS 2,991,647
CHROMATOGRAPHY Filed July 12, 1957 4 Sheets-Sheet 4 FIGURE I Rono J. Harris Inventor samples into the apparatus. 1 the sample also must be taken into account.
2,991,647 CHROMATOGRAPHY Rano Joseph Harris, Baton Rouge, La., assignor to Precision Instruments Company, a partnership in Louisiana Filed July 12, 1957, Ser. No. 671,573 3 Claims. (Cl. 73-23) The present invention relates to gas chromatography. It more particularly relates to a method and means for quickly and reproducibly injecting small samples into vapor-liquid partition adsorption chromatographic apparatus. V
In brief compass, this invention proposes an improved method for introducing exceedingly small liquid or gaseous samples into a carrier gas as used in chromatographic analysis. This improved method comprises flowing the carrier or eluting medium at a uniform rate through a passageway past an orifice or seating means and into a chromatographic column used for resolving the sample, and introducing the sample by means of a small capillary pipet into the carrier medium through the agency of the orifice. One end of the small capillary pipet matches and registers with the orifice in the passageway. The pipet contains a sample containing capillary bore, one end of which opens on the end of the pipet that matches with the orifice. The other end of the bore opens on the side of the pipet or other end. Thus, when the pipet is contact With the orifice, the eluting or carrier medium flows through the bore, purging it of its contents. Shortly after this, the pipet is withdrawn to permit continued passage of the carrier medium through the orifice into the column.
As it is known in the art in gas chromatography, small samples-usually 0.0001 to 1.0 ml. for liquids and 0.01 to 100 ml. of gases-must instantly and reproducibly be injected into the carrying fluid that transports the sample through the chromatographic column wherein resolution of the sample is attained. Besides the exceedingly small volumes involved, the fact that the flow of the carrying fluid must be substantially uniform and that the fluid is under pressure, further complicates injection of The volatility or viscosity of The present invention proposes a versatile method and apparatus for satisfactorily introducing samples, both liquid and gaseous, into chromatographic apparatus. This new method gives excellent reproducibility with essential- 1y no time lag and consequent loss in column resolution.
This invention will become clear from the following description of the drawing attached to and forming a part of this specification.
In the drawings, FIGURE I illustrates one type of chromatographic apparatus to which the sample inlet system of this invention is applicable;
FIGURE II illustrates one preferred embodiment of the sample inlet system of this invention;
FIGURE III illustrates one type of pipet assembly adapted to handle liquids;
FIGURE IV illustrates one type of pipet assembly adapted to handle gases; and
FIGURE V illustrates some modifications of the apparatus of this invention.
Referring now to FIGURE I, illustrated is a chromatographic column =1 filled with an adsorptive solid or, as in this example, an inert, relatively porous packing, such as crushed firebrick 2. Carried on this firebrick is an absorbent material, usually a high molecular weight liquid such as an oil or soap, e.g., a heavy lubricating oil. A carrier fluid supplied by line 3 is admitted to the inlet of column 1. This carrier fluid is preferably first passed through the detection means 6 by line 8 so that a simple differential analysis can be made. For the purpose of this example of vapor-liquid partition chromatography, the fluid is helium although equivalent gases, such as nitrogen, can be used. It is important, in order to obtain reproducible results, that the flow of the carrier fluid through the column be substantially uniform and constant.
The whole of the system so far described is maintained within a furnace or other similarly heated chamber 5, so that a substantially uniform temperature can be maintained. The temperature used generally is in the range from 0 to 600 F. The helium gas, in passing through coil 3a, is heated up to the operating temperature.
In general, this type of chromatographic apparatus operates by injection of a small sample-say, a mixture of C to C hydrocarbons-into the carrier fluid, as by line 9. The sample can be heated at the point of injection to assist the rapid vaporization of higher boiling materials. The hydrocarbon components of the sample are then carried through the column, being picked up in part by the absorbent and then being deabsorbed at different time intervals, whereby they are separated or resolved. Some time after injection of the sample, say 1 to 30 minutes, the first component of the sample appears in the gases emerging from the column and its presence is detected in the helium gas by a detector 6, and each component-as it appears in the exit gas-is similarly detected. After having passed through the detection apparatus, the gases can be vented by line 7 or collected as desired.
The sample, in passing through the column, is resolved because of the differences in the vapor-liquid equilibria for each component of the sample with respect to the absorbent in the column. These different components of a sample emerge at different characteristic times for a given set of operating conditions.
Detector 6 is used to measure some physical characteristic of the gas, such as thermal conductivity, density, charged particle ionization characteristics, infra red radiation absorption, etc. It is customary to measure the characteristic of the exit gas relative to the incoming carrier gas to obtain a more accurate and simpler analysis. The detector can consist, for example, of a means of measuring the thermal conductivity of the exit gas rela tive to that of the incoming carrier gas. Thus, as the different components of the sample appear in the exit helium carrier gas, the thermal conductivity will change. The identity of a compound in the sample causing a change in thermal conductivity is obtained by calibration of the apparatus with respect to time. For a given set of operating conditions, any single compound will have a characteristic time of appearance in the exit carrier gas relative to the time of injection of the sample. This information, e.g., change in thermal conductivity, ob tained by detector'6 is customarily plotted against time. The amount of the compound in the sample can then be determined from the height or magnitude in the change recorded by the detector, or more properly can be obtained by the area under the curve caused by the compound.
The above description is intended to be only exemplary of apparatus to which the improvement of this invention is applicable. Similar apparatus can, of course, be used.
The improvement of this invention relates to the manner of introducing the small sample into the system. The sample inlet system of this invention as shown in FIG- URE I, is to the right of connection 4 connecting the inlet system to the initial portion of the chromatographic column, indicated generally as line 9.
Referring to FIGURE II, this inlet system comprises in one embodiment an inlet conduit 11 connecting with connection 4, into which the helium gas in line 3a is introduced. An orifice or seating arrangement 10 is placed within conduit 11 downstream of the point of carrier gas admission. Orifice I10 is here shown as being integral with connection 4, but this is not necessary. Orifice 10 can be made of yielding rubber, Teflon (Du- Pont trademark for fluorine containing ethylene resin), or similar plastic. For high temperature service, brass, stainless steel, or similar metals can be used. Conduit 11 terminates in a valve 14 of the stopcock or plug valve type that, when open, permits passage of a rod or tube into conduit 11, as explained below. Another conduit 15, extending from the other side of valve 14, terminates in a sealing means 16 which, in this case, comprises an ring seal 17. A bracket 12 is used to attach the inlet system to the cabinet containing the chromatographic column, the bracket also supporting valve 14 by bolt 13.
In normal operation valve 14 is closed and helium from line 3 continuously flows at a uniform rate in line 11, through orifice 10, and into colum 1.
The sample carrier of this invention, shown in FIG- URE III, comprises a small pipet 29 which has a small capillary bore 18. The end of this pipet registers or matches with orifice 10, and is preferably precision shaped or ground to a taper angle of 15 to 45". As shown in the enlargement, it is especially preferred to give the tip of the pipet an additional taper to aid in guiding it into the orifice. The fit of the pipet with the orifice is such that the shoulder of the orifice, which need not be knife-edged as shown, evenly circumferentially contacts the taper of the pipet. A suitable orifice of another type can comprise a plastic O-ring held in place by a ring retainer in coupling 4. The upstream side of orifice can also be tapered as illustrated to aid in guiding the pipet. One end of the capillary bore 18 terminates in the end of the capillary pipet that registers with the orifice, so that the bore is aligned to discharge its con- ,tents on the other side of the orifice. The other end of the capillary bore is exposed to the carrier fluid or gas in line 11, supplied by line 3a.
In a much preferred embodiment of this invention, the capillary bore of the pipet is specially made such that the ends are of smaller diameter or cross-sectional area than the central section. This is to prevent undue loss of the sample, especially with gaseous or volatile liquids. With a liquid handling pipet, the diameter of the inlet to bore is in the order of 0.05 to 0.5 mm., and the diameter in the middle is in the order of 0.1 to 5.0 mm. For gases, the inlet to the bore is in the order of 0.05 to 1.0 mm. in diameter, and the middle of the bore can be up to 5.0 mm. or more in diameter, so long as piston fiow is achieved during discharge of the sample. The capacity of the pipet for liquid samples is preferably in the range of 0.0001 to 1.0 ml. The capacity for gas samples is substantially larger and is preferably in the range of .01 to 100 ml. For ease of cleaning, and to permit observation of the sample, the smaller pipets for liquids are preferably made of glass, although they can be made of metal or other suitable materials. The larger metal pipets for gas samples are preferably made of stainless steel to avoid contamination problems.
The bore of the pipet, While it can run longitudinally through the pipet, is preferably turned as shown to emerge on the side of the pipet. This permits convenient in line attachment of a handle 19 to the pipet.
The pipet can be loaded in several ways. One way, when handling liquid, is simply to insert the end of it in the liquid and allow capillary action to draw in the sample. It can be purged, when handling gases, with the desired gas to be filled. Alternatively, a hypodermic needle or aspirator bulb can be used to fill the capillary bore.
Th capillary pipet carrying the sample is inserted into the sample inlet system by inserting pipet 20 through sealing means 17, up to valve 14 which is closed. It is preferred to purge line before insertion of the pipet as by bleeding carrier gas through valve 14, or by means of a purge line 22, shown in FIGURE II. Valve 14 can also be a 3-way valve or can be drilled to permit passage of purge gas to line 15.
Pipet 20 is of smaller diameter, preferably, than handle 19. The 0 ring seal 17 mates with handle 19, and provides a firm fit. In some cases the column may be operated under pressure as high as 50 psi. or more, and the design of sealing means 1 6 is sufficient to prevent any appreciable loss of gas. A mark can be placed on handle 19 to tell when the pipet is approaching valve 14. After handle 19 makes a seal with 0 ring seal 17, valve 14 is opened and the passage of the pipet is continued until contact is made with orifice 10.
Upon contact with orifice 10, the contents of pipet 20 are discharged because the flow of the carrying fluid is temporarily interrupted and thus forced through capillary bore 18, expelling or purging it of its contents. Within a few seconds, e.g., l-20, depending on the size of the pipet, the pipet is Withdrawn to allow continued passage of the carrying fluid without substantial interruption.
The pipet shown in FIGURE III is designed primarily for liquids. To accommodate gases, the capillary bore can simply be expanded but this may be disadvantageous for large gas samples, i.e., greater than 1 00., in that nonpiston flow may attain and thus result in an appreciable time lag in purging the bore. For this reason, when it is necessary to handle a large volume of gas, the apparatus of FIGURE IV may be preferred. In this arrangement, a pipet 30 contains what might be termed a capillary tube 31. For example, this may comprise small bore steel tubing, e.g., 0.01 to 0.25 inch I.D., such as used in hypodermic needles. This tube extends from the end of the pipet that registers with the orifice, through the opposite end of handle 32, and is curved or coiled at 33 to provide the requisite volume. The other end of the capillary tube is then passed back Within to the pipet, and emerges through the side wall of the pipet at 34. As an example, pipet 30 can have an outside diameter of i -inch, and the handle can have a diameter of about fit-illch. The capillary tube can have a bore of A -inch and an overall length of 6 feet. It is convenient to provide quick couplings or connectors 35 on tubing 31 as shown, to permit ready attachment of coils of different sizes to the pipet, and thus to permit ready adustment of the capacity of the gas pipet. Also, it is convenient to incorporate coil 33 in an enlarged handle, not illustrated, attached to handle 32, to permit easier handling of the pipet.
In one particularly preferred embodiment of this invention, the external surface of the pipet handle 19 (See FIGURE III) is Teflon, or similar plastic. The lubricity of Teflon permits smooth insertion of the pipet into the sample inlet system. For example, handle 19 can be coated with Teflon, or can be entirely made of Teflon with pipet 20 fitting therein by a press fit, as shown. The latter construction is advantageous when glass pipets are used because it gives some flexibility to the pipet assembly.
The lubricating characteristics of Teflon can also be used to advantage in valve 14. It is preferred to form the rotating plug of the valve from Teflon to eliminate the need for a lubricating grease which might cause sample contamination.
In FIGURE V some modifications of the invention are shown. In FIGURE V, parts similar to those illustrated in FIGURE II bear the same identification numbers.
When a sample is volatile, some of the sample can be lost by premature volatilization of the sample. This can be satisfactorily overcome by precooling of the pipet and/or sample. For example, the pipet can be immersed in liquid nitrogen before, and after, if desired, the sample is placed in the pipet.
With viscous and relatively non-volatile samples, it is desirable to supply heat to the pipet to permit removal of the sample by the carrier gas. Otherwise, substantially instantaneous introduction of the sample might not be attained, and the results might not be as accurate as desired, e.g., peak heights for the individual components may be affected. This heating can be done by externally heating the sample, but this can result in premature volatilization and partial loss of the sample.
As illustrated in FIGURE V, one means of heating the pipet at the point of introduction, is to externally heat orifice 10, as by heating coils 50, which can comprise, for example, an electric heating tape. To enhance the rapid heating of the sample, a heating and dispersing means 51 can also be placed behind the orifice, usch as a metal frit, several layers of fine screen, etc. This can be yieldingly held in place by a spring 52 which permits the end of the pipet to contact means 51 without danger of breakage.
When the chromatographic column is running at a relatively high temperature, or when heating means 50 is used, it may be desirable to prevent the transfer of heat by pipe 11 outwards to valve 14, for example, to protect plastic parts or lubricant in the valve, and to prevent premature volatilization of liquid samples. This can be done by wrapping a cooling coil about pipe 11, or, as illustrated for the particular arrangement shown, by attaching cooling fins 55 to pipe 11.
As an example with reference to FIGURE III, a pipet adapted for liquid samples is formed from a %;-inch 0.D. pyrex glass tube, 4- /8 inches long. The length of the capillary bore therein is about /2 inch, and has a capacity of 0.00159 ml. This glass tubing is supported by a handle formed from a Ai-inch O.D. Teflon rod, 7 inches long, the glass tubing fitting by a press fit 1 inch into the handle.
To test the precision of this pipet for introducing liquid samples, normal hexane was introduced twenty times via the pipet into a Perkin-Elmer Fractometer System operating at 25 p.s.i.g., with a helium flow rate of 120 ml. per minute (at one atmosphere and room temperature). The column was operated at 50 C., using 10 ft. of 30% l-octadecene on No. 545 Celite. Using the measured peak heights, the 95% confidence limits for the peak heights were found to be i 0.89% of the peak height, which is highly satisfactory.
It can be seen that this invention permits substantially instantaneous and reproducible introduction of samples of known and constant volume into chromatographic apparatus. Operator error is eliminated in measuring the samples. It is not necessary to normalize the results obtained by the method of this invention, which must be done with the prior art apparatus, and the system can readily be used for partial component analysis.
Further descriptions and examples of this invention can be found in the following articles:
Sample Introduction System for Gas Chromatography, Tenney and Harris, Analytical Chemistry, vol. 29, No. 2, pps. 317-318, February 1957.
"Greater Precision with the Fisher-Gulf Partitioner, The Laboratory, vol. 25, No. 4, pps. 116-117, Fisher Scientific Company, Publisher.
Having described this invention, what is sought to be protected by Letters Patent is succinctly set forth in the following claims.
What is claimed is:
1. Apparatus for chromatographic analysis which comprises a chromatographic column, an inlet conduit for passing a carrying fluid to said column, a seating means Within said inlet conduit and a capillary pipet removably fitting with the upstream side of said seating means, said pipet comprising a small elongated rod with an open ended capillary bore, one end of which opens in the face of said pipet that registers with said seating means and the other end of said bore opening within said inlet conduit when said pipet is in contact with said seating means whereby, when the pipet is seated in said seating means, said carrying fluid is caused to flow through said bore and the contents of said capillary bore are expelled by said carrying fluid through said seating means and into said column.
2. The apparatus of claim 1 wherein said inlet conduit includes inlet means for admitting and contacting said pipet with said seating means while maintaining a pressure seal, said inlet means comprising a branched conduit for introducing said carrying fluid into said inlet conduit upstream of said seating means, a valve in said conduit beyond said branched conduit adapted to provide passage when open for said pipet, and a sealing means beyond said valve providing a yielding fit about the rearward portion of said pipet, and forming therewith a moderately tight seal.
3. A pipet for introducing small fluid samples into chromatographic apparatus which comprises a small elongated member having a capillary bore open at both ends, one end of said bore opening in the central portion of one face of said elongated member, and an aligned handle substantially longer than said elongated member and attached to said elongated member at the opposite end from said face, said handle being larger in diameter and substantially longer than said elongated member and said here comprising capillary tubing which extends from said face through the other end of said elongated member and handle to a coil, the other end of said tubing returning through said handle and elongated member and terminating and opening on a side wall of said elongated member.
References Cited in the file of this patent UNITED STATES PATENTS Gas Chromatography II, by N. H. Ray in Journal of Applied Chemistry, vol. 4, p. 82, Feb. 1954, pp. 82-85.
Gas Chromatograph in Oil and Gas Journal, Dec. 17, 1956, pp. 126-14 Book: Vapor Phase Chromatograph (Desty), Butterworth Scientific Publications, London, 1956, pages 287, 423.
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|U.S. Classification||73/864.82, 96/105, 73/23.35, 73/23.39|
|International Classification||G01N30/16, G01N30/00|