US 3798973 A
A method for providing enhanced stream splitting is provided by conveying a plug comprising a mixture of a sample material and carrier gas to a stream splitting means and initially dividing a leading portion of the plug during a relatively short interval of time into a measurement component and into a discharge component. The division or split ratio is automatically altered to a second value according to which the remaining and principal portion of the plug is divided by conveying the discharge component through a discharge volume which is relatively small with respect to the volume of the plug and through a flow restriction to atmosphere. The measurement component of the plug is simultaneously conveyed toward a chromatographic column. The second split ratio is thereby maintained substantially constant for the passage of the remaining and principal portion of the plug past a split station of the stream splitting means.
Claims available in
Description (OCR text may contain errors)
United States Patent [191 Estey SAMPLE METHOD AND ARRANGEMENT FOR GAS CHROMATOGRAPH Willard E. Estey, Ridgefield, Conn.
 Assignee: The Perkin-Elmer Corporation,
22 Filed: July 14,1972
211 Appl. No.: 271,901
 US. Cl. 73/422 GC, 73/23.l  Int. Cl G01r 1/10  Field of Search 73/422 GC, 23.1
 References Cited FOREIGN PATENTS OR APPLICATIONS 971,678 9/1964 Great Britain 73/23.]
Primary ExaminerS. Clement Swisher Attorney, Agent, or Firm-Daniel R. Levinson  ABSTRACT A method for providing enhanced stream splitting is provided by conveying a plug comprising a mixture of a sample material and carrier gas to a stream splitting means and initially dividing a leading portion of the plug during a relatively short interval of time into a measurement component and into a discharge compo- Man-26, 1974 graphic column. The second split ratio is thereby maintained substantially constant for the passage of the remaining and principal portion of the plug past a split station of the stream splitting means.
A chromatographic apparatus in accordance with features of the invention comprises a stream splitting means, means providing a flow channel communicating between a first outlet of the stream splitting means and a separating column, and means providing a second flow channel communicating between a second outlet of the stream splitting means and a flow restrictor 'means which is vented to atmosphere. The second flow channel has a relatively small volume for providing that a discharge component of the plug which flows therein after splitting is rapidly vented to atmosphere. In a particular embodiment, the discharge volume is substantially less in magnitude than the volume of the plug.
8 Claims, 13 Drawing Figures 7'0 COLUMN PAIENIEDIIARZB i974 SHEET 3 OF 3 SAMPLE METHOD AND ARRANGEMENT FOR GAS CHROMATOGRAPH This invention relates to gas chromatography. The invention relates more particularly to an improved sample injection and stream splitting method and arrangement for use with a gas chromatograph.
A gas chromatograph, as is known, is an analytical instrument which separates a sample material into constituents by conveying a plug comprising a mixture of sample material in a vaporized state and a substantially larger volume of carrier gas through a separating column. The constituents which experience different transit times through the column elute successively in time from the column to provide a quantitative indication of the constituents of the sample. An effluent of the column is coupled to a detection and indicating means which senses the occurrence of generally bell shaped peaks associated with each of the constituents and which provides an indication of their height, area and shape. 7
Two general types of separating columns are presently utilized with gas chromatographs. One form of chromatographic column comprises an elongated capillary or open tubular column which is coated on an inner surface thereof with a separating medium. Alternatively, a support material is formed as an open tubular liner within the capillary column, and the separating medium is deposited on the support material. A second type of chromatographic column comprises an elongated tube which is packed with a support material and upon which the separating medium is deposited. Each of these types of columns exhibits desirable characteristics which are useful in separating the components of particular sample materials.
The capillary or open tubular column has an operating characteristic which necessitates the introduction ofa relatively smaller plug quantity than can be accommodated by a packed column. The plug volume which can be handled by a capillary column is generally on the order of 1/10 to l/10,000 of the quantity which is applied to a packed column. The corresponding small sample quantity renders the sample impractical to handle. In accordance with present techniques, sample volumes within the range of about 0.5 to l microliters are introduced to the instrument at an injection station and form substantially larger plug mixtures with the carrier gas. The plug quantity is then automatically reduced by a stream splitting means prior to entry onto a capillary column. The stream splitting means divides the plug in accordance with a predetermined split ratio into a relatively small quantity measurement component which flows to the column'and into a relatively large quantity discharge component which is conveyed through a discharge volume and flow restriction to atmosphere.
In order to provide meaningful analytical results, it is desirable that the plug of sample material and carrier gas be substantially fully homogenized before stream splitting occurs. When this condition is not achieved, non-linearities which can be introduced by the stream splitting means interefere with the separation and reduce its accuracy. In practice, however, full homogenization is not always achieved and attempts have been made to reduce stream splitting non-linearities. More particularly, linearity occurs when the flow rate of the plug sample mixture remains relatively constant during the passage of the plug past the stream splitting point or junction. In general, the carrier gas exhibits relatively constant velocity or flow rate as it goes through the various flow paths and channels of the inlet system of the chromatograph. However, as the discharge component of the plug reaches a venting flow restrictor, and goes through the restrictor to atmosphere, the flow rate of the plug is altered. This variation in flow rate represents a change in rate at which another portion of the plug passes the split point. The result of this is an undesirable alteration in the amount of sample or measuring component of the plug which flows to the column after this variation in splitting time occurs which differs with respect to the quantity of the measuring component of the plug flowing to the column prior to the plug passing the exit restrictor. Less than complete homogenization of the plug prior to splitting in a nonlinear system leads to inaccurate results.
One stream splitting arrangement which overcomes this undesirable non-linear affect includes a discharge channel having a volume which is greater than thevolume of the largest plug expected to be handled by the instrument. The use of this relatively large discharge volume then assures that the entire plug will have passed the split station before a leading front of the discharge component of the plug reaches the flow restriction and is vented to atmosphere. The flow viscosity of the discharge component of the plug and the downstream pressure is then maintained relatively constant throughout the occurrence of the split. While this arrangement has provided highly useful and advantageous results, it necessitates the use of a relatively large discharge volume thereby undesirably increasing the size of the injection and stream splitting means. For example, although the sample quantities are on the order of 0.5 to 10 microliters, the plug mixture for these quantities can have a typical volume of 5 cc. Furthermore, the instrument operator is required to limit the quantity of the plug to a volume which is less than the volume of the discharge channel. This can then limit the sample quantity and carrier flow rates which can be employed. At times this requirement is not fulfilled and the stream splitting ratio is disadvantageously affected.
In additionto relatively large size requirements for the open tubular column injection and stream splitting means and an accompanying relatively high cost, the replacement of a packed column injection means with the open tubular injection and stream splitting means has required a partial disassembly of the instrument. This, of course, disadvantageously limits the ready adaptability of the instrument.
Accordingly, it is an object of this invention to provide an improved stream splitting method and arrangement for use with open tubular gas chromatographic separating column.
Another object of the invention is to provide an improved injection arrangement for a gas chromatograph.
Another object of the invention is to provide an improved stream-splitting means for use with a gas chromatograph which provides a substantially uniform splitting ratio during transit of a plug past a stream splitting station.
Another object of the invention is to provide an improved injection and stream-splitting arrangement for an open tubular column having a size adapted which is readily interchangeable with packed column injection and stream splitting means of present day chromatographs.
Another object of the invention is to provide an improved open tubular column injection and stream splitting arrangement having a relatively small size, yet which provides substantial linearity in stream splitting.
Another object of the invention is to provide a sample injection and stream splitting arrangement for open tubular columns which can be fabricated at substantially less cost than present day arrangements.
A further object of the invention is to provide an improved injection arrangement which provides enhanced sample-carrier gas mixing and homogenization.
' In accordance with the general features of the method of this invention, a plug comprising a mixture of a sample material and carrier gas is conveyed to a stream splitting means and a leading portion thereof is initially divided during a relatively short interval of time into a measurement component and into a discharge component. .The division is automatically altered to a second value according to which the remaining and principal portion of the plug is divided by conveying the discharge component through a relatively small discharge volume and flow restriction to atmosphere. The measurement component of the plug is simultaneously conveyed toward a chromatographic column. The second split ratio is thereby maintained substantially constant for the transit of the remaining and principal portion of the plug past a split station of the stream splitting means. The discharge component of the plug is preferably vented to atmosphere simultaneously with the initial splitting of the plug into measurement and discharge quantities. However, a practical discharge volume must exhibit finite dimensions, and a relatively short transit time is required for conveying the dishcarge component from the split station to atmosphere.
A chromatographic apparatus in accordance with features of the invention comprises a stream splitting means,'means providing a flow channel communicating between a first outlet of the stream splitting means and a separating column, and means providing a second flow channel communicating between a second outlet of the stream splitting means and a' flow restrictor means which-is vented to atmosphere. The second flow channel has a relatively small volume for providing that a discharge component of the plug which flows therein after splitting is rapidly vented to atmosphere. In a particular embodiment, the discharge volume is substantially less in magnitude than the volume of the plug thereby providing a substantially constant flow rate of the plug past the splitting station.
In accordance with other features of the invention, mixing of the sample and carrier gas to provide a sample plug of enhanced homogenity is provided by a sample injector having a flow channel formed by a cylindrically shaped body and a plurality of segments of disc shaped stream diverting members supported within the cylinder and extending into the cylindrical flow passage alternatively from different circumferential locations on the inner surface of the cylinder. The carrier stream flowing through the cylinder thereby repeatedly alters its direction of passage and the resulting turbulence enhances mixing of the sample material and flowing carrier stream to provide a plug of enhanced homogenization.
These and other objects and'features of the invention will become apparent with reference to the following specification and to the drawingswherein:
FIG. 1 is a schematic diagram in block form illustrating a chromatographic apparatus incorporating features of the present invention;
FIG. 2 is a more detailed schematic view of a sample injection and stream splitting arrangement of FIG. 1;
FIGS. 3a,'3b and 3c are diagrammatic representations illustrating the transit of a plug mixture past a stream splitting station of a prior art arrangement;
FIGS. 4a, 4b and 4c are diagrammatic representations illustrating the transit of a plug mixture past a stream splitting station and which is useful in describing the operation of the present invention;
FIG. 5 is a side elevation view, partly in section, illustrating an injector and stream splitting arrangement constructed in accordance with features of the present invention;
FIG. 6 is a sectional view taken along lines 6-6 of FIG. 5;
FIG. 7 is a sectional view taken along lines 7-7 of FIG. 5;
FIG. 8 is a sectional view taken-along lines 88 of I FIG. 5; and,
FIG. 9 is an enlarged view of a portion of FIG. 5.
Referring now to FIG. 1, the chromatographic instrument illustrated therein includes a source of carrier gas 10. Carrier gas is conveyed by a suitable tubulation 11 from the source 10 to an injector and stream splitting means 12. The injector and stream splitting means 12 is demountably supported by a heated injector block 14 which maintains the injector andstream splitter at a desired temperature. The injector is adapted for receiving, vaporizing, and mixing a sample with the stream of the carrier gas. The sample which typically has a volume on the order of 0.5 to 10 microliters is introduced into the injector means 12 from a syringe 16. The sample thus inserted formsa mixture or plug of vaporized sample material and carrier gas, a measurement portion or component of which is conveyed to an open tubular chromatographic column 18 and a discharge portion or component of which is conveyed to atmosphere through a vent 20. The sample measurement component is transported through the column 18 and is separated into constituents which experience different tranof the injector sit times in the column. An effluent of the columnis coupled to a detector 22. The detector 22 which comprises, for example, an ionization detector, senses the occurrence of constituent peaks and provides an electrical indication thereof. This electrical indication is applied to an indicator, as for example, a strip chart recorder, which forms a chromatogram having a series of bell shaped peaks, the areas of which are indicative of the concentration of the associated constituents of the sample.
The injector and stream splitting means 12 is schematically illustrated in greater detail in FIG. 2. The syringe 16 includes a probe 24 which extends through a septum 26 into a relatively narrow bore tube 28. Carrier gas from the source 10 flows through a channel formed between the bore 28 and a concentrically located tube 29. The carrier gas flows into the bore 28 where it picks up the sample which is ejected by the probe 24. The sample thus deposited in the flowing carrier stream is transported to a mixing chamber where the sample is mixed with the carrier gas to provide a homogenized plug 31. The plug 31 will have a volume which is principally determined by the duration of injection and the carrier gas flow rate. For example, at a Sec/second carrier gas flow rate a one second injection time, and a one microliter sample quantity, the plug will have a volume of about 5cc. The plug flowing from the mixing chamber 30 flows toward a stream splitting station referenced by the dotted line 32. The plug is divided at the station 32 into a measurement component 33 which flows along a portion of a first channel 34 to the chromatographic column and into a discharge component 35 which flows through a discharge volume 36 to a flow restricting means 38. The effluent of this flow restricting means is vented to atmosphere. Atmospheric conditions for the purposes of this application represents the external environmental conditions under which an analytical instrument operates. The plug 31 is divided at the split station 32 in accordance with a predetermined ratio R. In general, the ratio R will have a value within the range of about 1/10 to about l/I0,000. The ratio R is determined principally by the flow restriction of the column connected to the channel 34, and the flow restriction provided by the flow restricting means 38 connected to channel 36.
As indicated hereinbefore, the split ratio R is disadvantageously subject to variation when the discharge component of a plug is vented to atmosphere before substantially the entire volume of the plug has completed its transit past the splitting station 32. Stated alternatively, the plug is undesirably subjected to a variation in flow rate during its transit at the splitting station. A prior arrangement for avoiding this variation in R is illustrated and described with respect to FIGS. 3a, 3b and 3c. The plug of sample material 31 is represented by the cross-hatched section. FIG. 3a illustrates the location of the plug as it reaches the stream splitting station 32. FIG. 3b illustrates the division of'the plug shortly after a leading from 42 of the plug has passed the station 32. It will be observed that at this time a portion of the measurement component 33 of the plug has entered the channel 34 on its passage to the open tubular chromatographic column. Similarly, a portion of relatively larger discharge component 35 has entered the discharge volume 36 on its passage toward the flow restriction 38. In FIG. 30, the plug has fully passed the split station 32 and a leading front 43 of the discharge component 35, which is fully located within the discharge channel 36 has not reached the flow restriction 38. As indicated hereinbefore, when the leading front 43 of the discharge plug component 35 flows through the restrictive means 38 while a portion of the plug is simultaneously in transit at the split station 32, then the flow rate of the plug is altered as it passes through orifree 38 because it has a viscosity different than the carrier which precedes the plug through the discharge channel. This alters the time in which sample is being split in a variation in the total amount of sample which flows to the column. The split ratio R is thus effectively altered. This is overcome as illustrated by the arrange ment of FIG. 30 wherein the discharge volume 36 extending between the split station 32 and the orifice 38 6 is made substantially larger than the volume of the plug 31.
In accordance with the present invention, and as illustrated in FIG. 4, a discharge component 35 of the plug is very rapidly conveyed to atmosphere upon passing the split station 32. By immediately conveying the discharge portion 35 of the plug to the flow restriction 38 and to atmosphere, the flow rate of the discharge component 35 is immediately altered from an initial value to a second substantially constant value corresponding to the downstream venting of the discharge component. It is noted that after this condition is achieved, the split ratio R will remain substantially constant throughout the interval while the remainder and principal portion of the plug is in transit past the split station 32. This advantageously provides for an enhanced split operation in that the split ratio R changes immediately from an initial value R to a second vaue R which value remains substantially constant throughout the transit of the remainder and principal portion of the plug past the split station 32. This rapid initial variation in split ratio is accomplished by providing a relatively small discharge volume 36. Preferably, the discharge volume 36 is substantially less than the volume of the plug. Its small size is limited by the practical requirements for providing a ventingmeans of finite dimensions which is adapted for supporting the flow restriction 38 and does not create greater flow impedance in'conjunction with the restriction 38 than can be tolerated for the desired split ratio. In addition to enhancing the linearity of operation, the relatively small discharge volume further contributes significantly to an overall reduction, in size of the injector and stream splitting means thereby rendering it interchangeably mountable withinjector means for packed column and substantially reducing its cost of fabrication.
A particular embodiment of an injector and stream splitting means constructed in accordance with this invention is illustrated in FIGS. 5 through 8. The chromatographic injector station includes the heater block 14 having an integral injector heater and support segment 50. The segment includes a bore extending longitudinally therethrough for receiving an injector assembly. A radially extending bore is formed in the heater block segment 50 for receiving a carrier gas inlet tubulation 52. The injector assembly which is demountably positioned in the segment 50 includes an elongated generally tubular shaped housing 54 having an integrally formed generally rectangular shaped segment 56 positioned at one end of this housing. As is indicated in greater detail hereinafter, the rectangular shaped segment 56 supports a flow restricting means and shut-off valve for conveying a discharge portion of a plug to atmosphere. Concentrically positioned in the injector housing 54 is a liner assembly which includes an elongated tubular shaped body 58 extending from an inlet or right hand end of the injector as viewed in FIG. 5 toward a central location within the injector housing 54. The liner assembly further comprises an elongated concentrically'located liner body 60 which-is formed of glass and which includes a generally conically shaped outlet end surface 62- which is seated against a conforming surface of an insert body 64 near one end of the cylindrical body 58. The liner body 60 includes a longitudinally extending bore 65 which extends between an injection station and the insert 64. As indicated in greater detail hereinafter, carrier gas flows through a channel which includes the bore 65 and a bore 66 which is formed in the insert body 64.. The conically shaped surface 62 is secured against a conforming surface of the insert 64 by a helical spring 68 which is positioned about the body and contacts a shoulder segment 70 thereof and by an elongated tubular sleeve 72 which is positioned about theliner 60. This assembly inhibits carrier gas from leaking from the tube 52 directly to the bore 66 without sweeping'past the sample injection station. The assembly of the liner body 60, the sleeve 72, and the cylindrical body 58 extend through a tubular shaped member 74 to a probe entry or injection station. The member 74 is fitted and brazed into a bore formed in the ring 56. An enlarged threaded outer surface 78 is formed near one end of the member 74 and a septum cap 79 engages this threaded surface. A probe penetrable cylindrically shaped septum 80 formed of rubber, for example, and an optionally used disc shaped septum shield 81 formed, for example, of Teflon are positioned within the cap 79. When the cap is mounted, the Teflon disc bears against one end of the sleeve 72 thereby exerting a force on the spring which seats the liner 60 against the insert 64. The septum 80 provides a probe penetrable seal through which the syringe needle or probe 24 (H6. 2) is introduced. The probe which is initially introduced through a bore 84 in the cap 79, through the septum 80, through the shield 81 and through a bore 86 in the sleeve 72, extends into the bore 65 of the liner 60.
Carrier gas flows to this injector assembly through the tubulation 52 and a bore 88 formed in the injector housing 54. The gas flows from the bore 88 to a concentrically located ring shaped channel formed between an inner surface of the housing 54 and an outer surface of the body 58. Carrier gas then flows through and from this ring shaped channel via a plurality of apertures 90 formed in the body 58 to a ring shaped channel extending between the inner surface of the body 58 and an outer surface of the sleeve 72 toward the spring 68. A ring shaped flow channel extends between an outer surface of the liner 60 and an inner surface of the sleeve 72. Carrier gas flowing toward the right as viewed in FIG. through this ring shaped channel flows into the bore 65 of the liner 60 and reverses its direction of flow. An outlet orifice of the probe 24 (FIG. 2) extends into the bore 65 and discharges a quantity of sample material into this flowing carrier stream. The carrier stream sweeps this mixture of sample and carrier through the bore 65 and toward a mixing chamber. The carrier gas conveys the sample quantity through the bore 66 of the insert 64 and through a spacer ring 104 to the mixing chamber 100, referenced generally The mixing chamber 100 is formed with a relatively wide cross-sectional area and a relatively short length in comparison with present day arrangements employed with open tubular columns. In order to provide a homogenized plug or mixture of carrier gas and sample, turbulence, the duration of mixing and the length of plug travel is effectively increased by providing an insert assembly of baffle members 102 which are positioned within the housing 54. These baffle members 102 comprise segments of discs which are secured to a rod 103 and extend from opposite sides of the inner surface of the injector housing 54. They have a segmented disc shape which conforms to a portion of the inner circumference of the housing 54 and a flat 105.
A flow passage 106 is provided between the flat of each member 102 and the inner surface of the housing 54. The flats 105 of adjacent members are alternately oppositely positioned. The direction of travel of the plug and carrier stream is thereby repeatedly altered by this baffle assembly and the transit time of the plug is thereby increased. An enhanced mixing and homogenization of the plug is thus provided.
The flowing carrier gas stream and plug which exit from the mixing chamber pass through a ring shaped spacer body 107, similar to 100, into a stream splitting member 108 having an outer diameter thereof which extends within the bore of the injector housing 54 and which is secured thereto by brazing, for example. The splitting member 108 has integrally formed therein a conically shaped bore 110 and a cylindrically shaped bore. A thin walled injector tube assembly 112 extends through the cylindrical bore toward the conical bore 110. The tube 112 includes a conically shaped tip 116 having an inlet orifice 118. The tube 112 further in-.
cludes a shoulder 114 of enlarged cross-section which locates the tube 112 against a shoulder formed near the junction of the integral, cylindrical and conical bores of the body 108 and provides accurate locating of the tip 116. A conventional swage lock means 119 secures the tube 112 within the split body 108. Carrier gas and the measurement component which flow in the tube 112 enter this tube through the origice 118 of the conical segment 116. A transverse plane, provided by the section lines 66 at the orifice, represents a stream split station equivalent to the split station 32 of FIGS. 2-4. The measuring plug component and carrier gas which flow through the orifice 1 18 is conveyed through the tube 112 and through a tubulation 120 and a column coupling means 122 to an open tubular separating column.
The discharge component of the plug is conveyed about the outer surface of the cone shaped member 116 and through a thin-walled tubulation 132 which is fitted into a radially extending bore 133 in the member 108. A recess 134 (P16. 7) is formed in and extends longitudinally through the wall of the housing 54. This recess is adapted for receiving and positioning the tubulation 132. The tubulation 132 extends along the length of the housing 54 within the recess 134 and extends into a bore 135 which communicates with an open space 136 formed in the rectangular shaped segment 56 of the injector housing 54. A cylindrically shaped flow restrictor support block 140 is positioned in the space 136 which is formed at an angle with respect to the axis of the injector and the rectangular shaped segment 56. This block which is brazed to the segment 56 includes an internal bore 142 threaded along a portion of its'length for receiving and engaging a flow restrictor 144. The flow restrictor is generally cylindrically shaped and includes a longitudinal bore extending therethrough of predetermined dimensions for establishing a desired flow impedance to the discharge component of the carrier gas and plug. The flow restrictor is threaded about an outside surface thereof and engages the internally threaded segment of the bore 142. The discharge component of the plug flows successively through the tubulation 132, and the bore 135, space 136, bore 142 and the bore of flow restrictor 144. I
A vent control is provided for alternatively providing a substantially unobstructed flow passage between the outlet of the restrictor 144 and atmosphere or for establishing a bleed vent for conserving carrier gas when a sample analysis is not in progress. The ventcontrol includes a tubular shaped vent port body 150 having internal threads which engage external threads formed on an outer surface of the block 140. An ring 152 provides a gas-tight seal at this union. A valve block 154 is fitted about the port body 150 at one end thereof and a gas-tight seal is provided therebetween by an 0 ring 156. The port body 150 includes an internal conically shaped end segment which converges to a bore 158 communicating with a bore 160 in the valve block 154. The valve block, which is annular shaped, includes a sliding valve member 162. This valve member is adapted to be positioned in a valve bleed position, as illustrated in FIG. 5, or in a vent position. In the bleed position, the bore 160 communicates with a bore 164 l in the slide body. A cylindrical bore 166 of enlarged cross-section is .formed in the slide body 162 and a body of sintered material 168 is positioned therein. The carrier gas and discharge plug component flow from the restrictor 144, through the bores 158, 160 and 164 and through the sintered material 168 to atmosphere. The sintered material establishes a flow impedance creating a back pressure which reduces the carrier flow and conserves the carrier gas when a sample analysis is not in progress. As an analysis is about to be initiated, the instrument operator actuates the slide 162 by pressing it in a generally upward direction thereby longitudinally translating the slide member and transferring a bore 170 and an outlet venting tube 172 into communication with the bore 160 and the valve body 154. The discharge component of carrier gas and the plug which flow from the restrictor 144 thereby flow through a relatively unobstructed flow passage to atmosphere. v
The injector and'stream splitting assembly are secured in the heater block 14 by a clamp 145 which engages the rectangular segment 56 of the housing 54 and which is screw mounted to the heater block segment 50. The assembly is thereby readily demountable by decoupling the column flow cover 122 and by removing the clamp 145.
The discharge component of the plug is conveyed to atmosphere almost immediately after passing the splitting station 32 by providing a relatively small discharge volume. The discharge volume comprises the volume between the outlet port 133 and the split station, the volume of the port 133, the volume of the tubulation 132, the volume of 'the port 135 and the space 136 leading to the flow restrictor 144. By providing a discharge volume which is relatively small, the discharge component of the plug is rapidly vented to atmosphere and the change in split ratio from R to R occurs immediately. The discharge volume is relatively small when this volume is substantially smaller than the volume of the plug. This is in contrast with prior arrangements wherein the discharge volume was made substantially larger than the volume of the plug.
As indicated hereinbefore, it is-desirable to provide an injection and stream splitting means for an open tubular chromatographic column which is relatively smaller than present day arrangements. In this regard, an interval of time, T during which the carrier gas and the sample which is injected into the carrier gas stream are mixed is significant because of the necessity of obtaining a homogeneous mixture prior to splitting. On
the other hand; it is desirable to maintain relatively short flow channels in order to provide a relatively compact injector system. In accordance with another feature of the invention, the mixing chamber of FIG. 5 provides a mixing time interval comparable with present day mixing chambers while still providing a relatively compact structural arrangement. This is accomplished by providing a relatively short mixing chamber length of relatively wide cross-section and by providing the flow diverting and turbulence disc members 102.
These members in addition to creating the increased turbulence which enhances the mixing of the carrier gas in the sample also effectively elongate the path over which this mixing occurs thereby increasing the interval of time during which mixing can occur over than which would be provided by a mixing chamber with this relatively shorter length.
In a particular embodiment of the invention, the discharge volume has a magnitude which at a predetermined carrier flow rate and within a range of split ratios, provides for the transit of a leading front 43 of the plug discharge component through the discharge volume in an interval of time equal to about 1 percent of the time required for the plug to traverse the split station and generally not exceeding about 2 h percent of this interval of time.
A particular injector and stream splitting arrangement not deemed limiting inany respect includes a mixing chamber having a length of about 5.49 centimeters, a diameter of about 0.952 centimeters and a discharge volume principally composed of the elongated tube 132 having a length of about 10.8 centimeters and a diameter of about 0.0635 centimeters. With an injector having a mixing chamber and discharge volume of these approximate dimensions, two samples were injected into the system. A first sample comprises a standard test mixture of C., to C straight chain hydrocarbons with -a boiling point range of from about' 93.5 to about 159C. Sample, sizes ranging in size from 0.5 to 10.0 microliters and a range of split ratios from 1:16 to 1:418 were employed and were separated on a 300 foot by 0.01 inch inside diameter wall coated column AP-L at split ratios of 1:74 to 1:418 as well as a 50 foot long 0.02 inch inside diameter support coated column AP-L with a split ratio of 1:16. Relatively good reproducible quantitative results were obtained. A second sample comprises a mixture of C to C straight chain hydrocarbons having a boiling point range of about 144C. to a vapor pressure of 40 MM at 282C. A gas chromatographic column oven was programmed during the, examination of this sample. The sample injection quantities which ranged from 0.5 to 8.0 microliters at relatively low split ratios were separated on a 50 foot long by 0.02 inch inside diameter sup'port coated open tubular column OV-l. In one test, the split ratio was 1:13 while in a second test the split ratio was 1:33. Good reproducible quantitativeresults were also obtained. In addition, no significant ghost peaks were produced with either of the examples.
There has thus been described an improved chromatographic injection and stream splitting method and apparatus wherein the stream splitting ratio of measurement -to discharge plug components is initially altered and is then maintained substantially constant. The arrangement is further advantageous in that it is relatively compact in size and is readily interchangeable with present day packed column injectors. The arrangement is economical in that it can be fabricated at a substantial cost savings over present day injection and stream splitting arrangements for open tubular columns.
While I have described particular embodiments of the invention, it will be apparent to those skilled in the art that variations may be made thereto without departing from the spirit of the invention and the scope of the appended claims.
What is claimed is:
l. A sample injection arrangement for a gas chromato-graph having an open tubular separating. column comprising:
an elongated generally tubular shaped housing memher;
a stream splitting body positioned atone end of said housing member and having an inlet aperture extending into a frustro-conically shaped bore;
said stream splitting body including a thin-walled conically shaped body positioned near a narrow portion of said frustro-conically shaped bore and forming with said frustro-conically shaped bore a stream splitting station;
means extending through said stream splitting body and communicating with said thin-walled conically shaped body for providing a flow passage between an inlet of said conically shaped body and an open tubular column;
a channel formed in said stream splitting body between said frustro-conically shaped bore and an outer surface of said body;
a flow impedance; and,
an elongated body coupled between said aperture in said stream splitting means and said flow impedance means;
said flow impedance means having an outlet aperture exposed to atmospheric conditions.
2. The apparatus of claim 1 wherein said elongated body has a volume which is substantially less than the volume of a sample mixture adapted to be accommodated by said instrument.
3. The apparatus of claim 2 wherein said tubular housing has a longitudinal axis, a recess formed in said body and extending in a direction substantially parallel to saidaxis, and said elongated body is positioned in said recess. I
4. The apparatus of claim 1 including means positioned within said tubular housing for mixing the sample and carrier gas, said means comprising a plurality of disc segments extending in a generally radial direction within said housing from different circumferential locations within said housing and positioned at different longitudinal sections in said housing.
5. The apparatus of claim 4 wherein a flow-channel is provided for conveying a sample quantity and carrier gas to said mixing chamber and said disc segments are positioned circumferentially within said housing for causing a carrier gas stream flowing therethrough to repeatedly alter the direction of flow.
6. The apparatus of claim 5 wherein said disc segments are assembled and secured to a rod and said assembly is adapted for insertion and removal from said housing. I
7. A method for supplying a relatively small portion of a mixture of a sample material and a carrier gas to a chromatographic separating column with apparatus having a conduit for conducting a stream containing a given quantity of said mixture to stream splitting means that splits the stream in a predetermined ratio into a relatively small measurement component, which is carried by a first channel to said column, and a relatively large discharge component, which is carried by a second channel to flow restricting means through which .the discharge components is vented, said method comprising:
providing a second channel whose volume between i said splitting means and said flow restricting means is substantially less than the volume of said quantity of mixture supplied, and selecting the amount of flow restriction of said flow restricting means and said volume of the second channel in relation to each other and in relation to the flow rate of said mixture to'the stream splitting means for the leading front of said discharge component to pass through said second channel and said flow restricting means in not more than 2 V; percent of the time it takes for said quantity of said mixture to pass said stream splitting means. 8. The method of claim 7 in which the time for the leading front of the discharge component to pass through the second channel and flow restricting means is about 1 percent of the time it takes for said quantity of said mixture to pass said stream splitting means.