US3681998A

US3681998A - Sample valve for chromatographic apparatus

Info

Publication number: US3681998A
Authority: US
Inventors: Edwin L Karas; David S Lee; Robert A Vanslette
Original assignee: Foxboro Co
Current assignee: Schneider Electric Systems USA Inc
Priority date: 1969-06-02
Filing date: 1969-06-02
Publication date: 1972-08-08
Anticipated expiration: 1989-08-08
Also published as: GB1286341A; JPS4924713B1

Abstract

Chromatographic apparatus is described wherein the improvement comprises a sample valve including slidably engaged members formed of a hard, wear-resistant alumina lapped to a high degree of flatness. These valve members are adapted to be molded using relatively inexpensive techniques. The engaged surfaces of the valve present cooperating ports and cavities which are adapted, when the valve members are shifted from one position to another, to inject a fixed amount of a sample mixture into a column. The valve surfaces also are formed with grooves carrying a flow of carrier to aid in isolating the injection ports from adjacent sample ports.

Description

United States Patent Karas et a1. [45] A 8, 1972 [54] SAMPLE VALVE FOR 3,150,517 9/1964 Kuffer et a1. ..73/422 GC X CHROMATOGRAPHIC APPARATUS 3,297,053 l/1967 Mcl (inney ..73/422 GC UX [72] Inventors: Edwin L. Rams, Sharon; David 8. 3,349,800 10/1967 Henon et a1 ..137/625 .66 3,442,285 5/1969 Faustim ..137/246.22 X Lee, North Easton, Robert A. Vanslette, M fi all of Mass 3,489,01 1 1/197() Firman 61 a1. ..73/422 GL [73] Assignee: The Foxboro Company, Foxboro, P i E i i R P i Mass- Assistant Examiner-Daniel M. Yasich [22] Filed; June 72, 1969 Attomey-Bryan, Parmelee, Johnson & Bollinger [21] Appl. N0.: 829,576 57 ABSTRACT Chromatographic apparatus is described wherein the [52] U.S. C1. ....73/422 GC, 73/42 improvement comprises a sample valve including slidably engaged members formed of a hard, wear-re- [51] [11L C1 ..G0ln 1/10, F16k 25/00 sistam alumina lapped to a i degree of flatness [58] Fleld 0f Search...73/23 R, 23.1, 421 R, 422 CC, These valve members are adapted to be molded using 73,4215 {37/146, 2 relatively inexpensive techniques. The engaged sur- 251/368 51/27 faces of the valve present cooperating ports and cavi- 56 R f Cted ties which are adapted, when the valve members are 1 e erences shifted from one position to another, to inject a fixed UNTTED STATES PATENTS amount of a sample mixture into a column. The valve surfaces also are formed with grooves carrying a flow 3,116,642 1/1964 Weir ..73/422 GC of carrier to aid in isolating the injection ports f 3,040,770 6/1962 Boettcher et a1. .....25l/368 X adjacent Sample pom 2,981,092 4/ 1961 Marks ..73/422 GC X 3,070,990 1/1963 Krinov ..73/421.5l R X 17 Claims, 8 Drawing figures NIX TURE SUI-PL Y CHER/ER S PPL Y PATENTED E 8 1972 SHEET 101 4 PATENTED 8 I973 3.681.998

SHEET 3 OF 4 HI" il 95' 1/0 My W h a II W' H 4 g H INVENTORS'. Eda/ h L lfaras flara? 5. ZL6

BY Haber? fl, Vaizsieile M, 3/7, Mg; m

1' v SAMPLE VALVE non CI-IROMAIOGRAPHIC APPARATUS separating components in a mixture by passing a sample of the mixture through a column containing a material which retains the components for difiering periods of time. Thus, the individual components emerge at different times from the column.'A detector placed at the output of the column provides an electrical signal in the form of a series of peaks, each reflecting'the concentration of a respective component.

The chromatographic technique is capable of determining the concentration of minute amounts of a cornponent in the mixture. To make fullest use of this capa bility, the sampling of the mixture must be carried out consistently and accurately. Specifically, the sample valve employed to inject a sample of the mixture into the column must be essentially leakproof, and must be capable of reliably metering a predetermined amount of sample each time it is actuated.

Over the past decade or so, a variety of different types of sample valves havebeen devised, some of which-have gone into extensive commercial use. However,notwithstanding extensive design efforts by many people, none of the sample valves has turned out to be truly satisfactory for the intended use. One of the principal problems with available valves is excessive wear with usage, leading ultimately to leaks requiring repair or replacement of the valve. For example, in conventional valves with sealing surfaces formed of stainless steel and Teflon, the valve may not last beyond 300,000 actuations. Moreover, conventional sample valves are inordinately expensive to manufacture. Thus, there has existed for some time an urgent need for a new valve design providing important improvements in longevity and reduced cost.

In a preferred embodiment of the invention to be described hereinbelow in detail, there is provided asample valve which will operate without significant leakage for a substantially greater number of operating cycles than conventional valves. This new valve moreover is relatively inexpensive to make. This new valve incorporates planar sealing surfaces molded of a very hard ceramic material, advantageously comprising alumina which has been found to be unusually well suited for this chromatographic application.

The deterioration of prior art sample valves often arises from scratching efiects caused by small hard particles that get in between the valve surfaces. The scratches in the valve surfaces destroy the fluid tightness of the valve which then becomes unable to provide an accurate sample for analysis, and permits leaks into the column which create errors. The valve of a hard, wear-resistant material presenting interac- 2 aspects and advantages derstood from the following description of a preferred embodiment of the invention considered together with the drawings wherein:

FIG. 1 is a block diagram and perspective view of a sample valve in. accordance with the invention as used in connection with a chromatographic instrument;

FIG. 2 is a perspective schematic representationv of fluid sampling port interconnections for the valve or FIG. 3 is a plan view of a valve slide employed with the valve ofFIG. l;

FIG. 4 is a sectional view of the valve slide taken along line 4-4 in FIG. 3;

FIG. Sis a plan view of a valve seat employed with the valve of FIG. 1;

FIG. 6 is a sectional view of the valve seat taken along line 6-6 in FIG. 5;

FIG. 7 is a section view of the mounted valve slide and seat taken along line 7-7 in FIG. 3; and

FIG. 8 is a plan view of the manifold employed with the valve of FIG. 1.

With reference now to FIG. 1, a chromatographic apparatus 10 utilizing a sample valve 12 of this invention is shown. The chromatographic apparatus employs a source 14 of carrier gas such as helium. The carrier gas is continuously supplied through the valve 12 to a conduit 34 leading to a chromatographic column sche matically shown at 16. (In a practical embodiment of the invention, the column 16 typically would consist of a small-diameter tube, wound in compact configuration, but has been shown as an upright element merely for illustrative purposes.)

At the output of the column 16 is a detector 18, such as a thermal-conductivity cell, to provide electrical signals representative of the various components separated by the column. The electrical signals are pased to a utilization device 20 which may include an electronic integrator, memory, display, controller, recorder and alarm, in various combinations as needed for utilization of the chromatographic measurement; The gases which emerge from the" column arevented at an exhaust port schematically indicated at 22.

The chromatographic instrument operates by injecting in series with the carrier gas stream flowing to the 1 column 16 a preselected amount of a mixture to be analyzed. A supply of the mixture is illustrated at 24. The mixture gas in the embodiment of FIG. 1 flows continuously through a conduit 26 to the valve and thence through another conduit ZSleading to a sample vent.

The valve 12 serves upon actuation to inject a precisely metered quantity of the mixture into the carrier gas stream flowing through conduit 34 to the column.

The valve 12 basically comprises two relatively'slidable parts, a valve slide 38 and a valve seat 40. Below the valve seat 40 is a manifold 42 which interconnects the several conduits with ports located in the valve interaction surfaces between the slide and the seat. The valve seat 40 is secured to the manifold 42 preferably by a sealant adhesive such as epoxy, and the manifold in 7 turn is supported by a suitable housing (not shown).

- The valve slide 38 and valve seat 40 are each formed of the invention will be untion surfaces lapped to a high degree of flatness and polished to a high degree of smoothness. The flatness after lapping is of the order of a quarter wavelength of light, that is, about 1 5 millionths of aninch. The preferred material is a ceramic comprising at least 80 percent alumina, and preferably between 90-95 percent alumina, the remainder being a suitable binder such as a glass silicate material, or the like.

The valve slide 38 is reciprocably shiftable along an axis 36 as by means of a suitable driver, such as a solenoid or air cylinder, not shown in the drawing. This valve slide is provided with a spring receiving recess 46 to receive a spring 48 used to urge the slide onto the seat 40. In order to maintain the slide in lateral alignment, the spring 48 acts at an inclined angle to the upper surface 50 of the slide to maintain the side surface of the slide in contact with an abutting cylindrical tube 52. The tube 52 is supported by the valve housing not shown in the drawing, and is made of the same material as the valve slide and seat.

The flatness and smoothness of the interaction surfaces between the valve slide and seat assures a close and tight fit between them, so as to effect a leakproof seal for the multiplicity of ports and passages. The spring 48 aids in this, and also aids in assuring that any particles which pass into the region between the valve slide and seat will be ground or abraded away by the hard ceramic interaction surfaces.

Referring now to FIGS. 2 and 3, the valve body 40 is formed with four pairs of centrally located

verticalpassages

62,72; 86,90 and 62,72'; 86,90 communicating between the manifold 42 and the top face of the valve body. The first two pairs of

passages

62,72; 86,90 are operative in injecting a sample into the column when the valve slide 38 is shifted in one direction, and the other two pairs 62,72'; 86',90' are operative in injecting a sample into the column when the slide is shifted in the other direction. That is, the valve is double acting, by injecting a prefixed amount of sample mixture when shifted in either direction. However, a single acting valve is also contemplated by the invention.-

Referring now also to FIGS. 5 and 6, the interaction face of the valve slide 38 is formed with a plurality of spaced

transverse grooves

70,80; 70,80'; 88,88 adapted to connect together the pairs of

valve body passages

62,72; 86,90, etc., in either position of the valve slide. In the position illustrated, groove 70 connects

passages

62 and 72, and groove 88 connects

passages

86 and 90, while the end groove 80 does not register with any passage. By causing sample mixture to flow up through passage 62, across groove 70 and down passage 72, groove 70 serves in effect as a metering" section to store a predetermined fixed amount of sample available at any time to be injected into the column. This sample mixture is supplied through conduit 26 and .rnanifold passage 66, and the flow out is through manifold passage 76 to a vent (not shown).

While groove 70 is thus being supplied with a flow of sample mixture, carrier gas simultaneously is-flowing up through valve seat passage 86, across the next adjacent groove 88 in valve slide 38, and down through valve seat passage 90 to theconduits leading to the column 16. By shifting the valve slide to the left (FIG. 2), groove 70 with its precisely metered amount of sample mixture is brought into registration with

passages

86 and 90. Thus the continued flow of carrier through these passages entrains the sample slug and forces it through the column for analysis.

The carrier gas flowing through groove 88 at injection station 54 comes from a manifold passage 82 connecting valve seat passage 86 to the carrier gas conduit 30 leading to supply 14. The output of injection station 54 is directed to the input of the other injection station 56 by a horizontal manifold channel 94. Thus upon shifting slide 38 to the left, the injected slug of sample from metering section groove follows the carrier gas path over to injection station 56, up valve seat passage 86, traverses groove 88' (which replaces groove 70) and flows down through passage '90 and an exit passage 94 out through conduit 34 to the column 16.

With the valve slide 38 in its leftward position, groove 70' is supplied with sample mixture through vertical passages 62' and 72' at sample station 58, venting from outlet passage 62' through manifold passage 78 and sample vent 28. The sample mixture passing up through inlet passage 72 is derived from conduit 26' leading to conduit 26 and thence to mixture supply 24. Thus when the valve slide is shifted back to its original position, this metered quantity of sample moves into registration with passages 86', 90 to be entrained by the continuing flow of carrier gas and thereby directed to the column 16 for analysis. The sample mixture connected to passage 72' may be a supply separate from supply 24, to provide redundancy assuring operation if one supply fails.

One of the important benefits of the valve construction described herein is that the operative parts can readily be molded or cast using relatively inexpensive known techniques. Thus, the valve seat and the valve slide can be made in corresponding dies comprising cavities into which may be placed the ceramic material as a powder, to form the green mold. The bottom surfaces of the die have a topography corresponding to the reverse of the desired shape of the interacting valve surfaces, i.e., predominantly flat sections with raised ridges to make the surface grooves and upstanding core members to make the vertical passages.

' This green form is fired at a high temperature in a furnace to-produce the hard ceramic parts. The flat interacting surfaces then are lapped to a fine degree of smoothness and flatness. Continued operation of the valve tends to improve the seal between the two interacting surfaces, as a result of the self-lapping action of planar surfaces. No lubricant is required between these surfaces, nor are special wedge shapes needed for effective sealing.

In operation, the extremely hard alumina ceramic is not scored by dirt, metal chips or other foreign material, as are the surfaces of conventional chromatographic valves. Wear tests have indicated actual improvement in the sealing surfaces with usage at least up to 750,000 valve actuations.

The available evidence suggests that valves in accordance with this aspect of the invention will have a life which may be upwards of ten times that of prior art valves.

The corrosion resistance of alumina is superior to stainless steel used in some prior chromatographic valves, thus minimizing a problem encountered in certain industrial applications. Ceramic also withstands higher temperatures than prior valves which included valve surfaces of plastic such as Teflon. Because of this high temperature capability, valves in accordance with the present invention advantageously may, if the ports become clogged with foreign substances, be cleaned simply by baking at an elevated temperature, e.g., high enough to oxidize gum, varnish and tars to a powder which may readily be removed.

A valve of this design may be quite compact, e.g., having an axial length of about 1 inch and a width of about three-quarters of an inch. The stroke in a typical unit may be about 0.14 inches. Preferably, resilient bumper stops are provided to cushion the ceramic material from excessive shock at the end of each stroke.

, If liquid sample mixtures are being analyzed, capillary action may tend to draw the sample material from the sample ports into the carrier passages leading to the column. To avoid such undesired contamination, the valve advantageously may be provided with what might be termed fluid shields around the sample injection stations 54 and 56. These fluid shields are composed of interconnected gutters through which carrier fluid from source 14 flows continuously to drain so as to intercept any leaking sample fluid and wash it away with the carrier. This carrier may be obtained from a source having a higher pressure than source 14, but in any event after passage through the shield is discarded through vents and not used in the columns. I

These gutters are formed in the interaction surfaces of the valve slide 38 and valve seat 40 which cooperates to form enclosed channels between the adjacent surfaces. These channels provide a closed rectangular shield around each of the two sample injection stations 54 and 56. The shields are operated in series, i.e., carrier first flows through one rectangular shield, then passes through an interconnecting channel 114 in the manifold 42 to the other shield, and from there to carrier vent passage 98 and vent conduit 32.

Specifically in reference to the fluid shields, carrier gas at either atmospheric or elevated pressure is first supplied from a flow controlled source (not shown) through shield passage l00102 in the manifold and valve seat respectively to a corner inlet port 104 in the valve seat. The carrier passes from the port 104 through two separate paths-to an opposite corner outlet port 106. One path comprises a first gutter 108 which connects to a comer recess 110, both being formed in the valve seat interaction surface; and a second gutter 112 which is formed transversely in the valve slide 38 and provides a carrier passage between the corner recess 110 and the comer outlet port 106. The second path includes transverse gutter 112' formed in the valve slide to connect to a comer recess 110' formed in the valve seat 40, and a second gutter 108' completing the path from the comer recess 110' to the outlet port 106. i

From the comer outlet port 106, the carrier flows down through interconnecting passage 113 and across channel 114 in the manifold to comer inlet port 104 in the rectangular shield around the other injection station 56. The arrangement of this shield is similar to the first shield and thus will not be described in detail.

From the view presented by FIG. 2, it will be appreciated that the injection stations and 56 are enclosed by fluid shields for both positions of the valve slide 38. This result is obtained by providing an additional transverse gutter 112" in the valve slide which is so spaced from gutter 112' that upon valve actuation into the alternate position the gutter 112" is placed where 112 previously was located (at station 54) and 112 is placed where gutter 112 was. In this manner gutter 112 is actually shared between the two fluid shields.

The reason for locating part of each fluid shield in the slide and the other'part in the valve seat is to disconnect the moving gutter passages from each other, thereby to prevent short circuitingthe sample ports directly to the injection ports during movement of the valve slide. The gutters in the valve slide disconnect completely from the valve seat gutters during transit so as to prevent injecting fluid into (or removing fluid from) the injection passages.

In some applications, it may be desirable to enhance the sealing between the valve manifold 42 and seat 40 by a similar shielding technique. Thus, as shown in FIG.

.8, a fluid shield is formed in surface 43 by etching a gutter around the several ports. The gutter 120 is fed with carrier at channel 122 communicating with passageway 82 and the carrier in the gutter 120 is removed at channel 124 leading to carrier vent conduit 98. 1

Although a specific preferred embodiment of the invention has been described hereinabove in detail, it is desired to emphasize that such detailed showing is for the principal purpose of illustrating the invention, and is not to be considered as limiting the scope thereof except as required by the prior art, it being understood that numerous modifications of the structure and techniques will be apparent to those skilled in-this art. For example, although the sample mixture metering section in the disclosed embodiment consists of a groove in the valve slide, it will be apparent that for larger samples it may be desirable to form vertical passages through the valve slide to make connection to relatively large volume metering tubes supported on the slide. It will also be apparent that the use of fluid shields is not limited to liquid applications, nor to the mixture metering valve only, but may be beneficial to various types of column switching and backflush valves as used in chromatographic instruments. For some applications, the valve seat and the manifold may be provided with additional passages to furnish a continuous flow of carrier gas through groove 88' in order to assure that no contamination accumulates in that groove. Furthermore, rotary instead of linear valve slide action may be employed with ports and passages and fluid shields correspondingly rotatably aligned. Other changes within the scope of the invention will be obvious.

We claim:

1. Chromatography apparatus including a sample valve for developing a metered amount of sample to be sent to the chromatographic column for analysis and comprising:

a valve slide and a valve seat slidingly mounted to one another with said valve slide and valve seat being provided with smooth valve interaction surfaces for fluid sealing engagement during relative motion between the valve slide and seat;

one of said interaction surfaces being provided with a sample storage passage means and the other interaction surface being provided with sample inlet and outlet ports located to align with the sample storage passage means at a first valve position;

the other interaction surface being provided with injection inlet and outlet ports located to align with the sample storage passage means at a second valve position; and

a fluid protective shield comprising a fluid channel between the interaction surfaces and positioned between the sample ports and the injection ports to serve as a barrier to prevent contamination of the fluid flowing to the column.

2. Apparatus as claimed in claim 1, including means to produce a continuous flow of carrier fluid through said channel.

3. Apparatus as claimed in claim 2, wherein the means producing said carrier fluid through said channel provides the carrier fluid at elevated pressure.

4. Apparatus as claimed in claim 2, wherein said fluid channel surrounds said injection ports when the valve slide and valve seat are in the non-injection position.

5. The sample valve as claimed in claim 1, wherein the valve seat and valve slide interaction surfaces are formed with interconnected carrier-filled gutters as said protective shield, the one interaction surface containing the sample storage passage means being provided with a pair of protective gutters flanking the sample storage passage means to assure shielding in alternate valve positions.

6. The sample valve as claimed in claim 1, wherein the fluid protective shield further includes a first pair'of parallel gutters formed in the other interaction surface containing the injection ports and flankingly located adjacent thereto, a second pair of parallel gutters formed in the one interaction surface in overlapping relationship with the first pair of gutters to provide fluid flow communication between the gutters around the injection ports.

7. The sample valve as claimed in claim 6, wherein the fluid protective shield further includes a third gutter located in said one interaction surface to effect a fluid protective shield around said injection ports in the injection positions.

8. The sample valve as claimed in claim 1, wherein the fluid channel includes valve seat and valve slide channels selectively located to prevent crossing of sample storage passages of said fluid channel.

9. A double-acting sampling valve for a chromatographic instrument comprising:

a valve slide and a valve seat slidingly mounted to one another with said seat and valve being provided with smooth valve interaction surfaces for fluid sealed engagement with relative motion between the valve slide and seat along a valve action axis;

said valve seat being provided with first sample inlet and outlet ports, first injection inlet and outlet ports axially located from the first sample ports,

second sample inlet and outlet ports located along the valve action axis and second injection inlet and outlet ports located between the second sample ports and the first injection ports;

said valve slide being provided with a first sample storage cavity sized and located for alternate operative engagement between the first sample and injection ports and further provided with a second sample storagecavity sized and located for alternate operative engagement between the second sample and injection ports;

a first relative position between the valve seat and slide locating the first sample storage cavity in registration with the first sample ports and the second sample storage cavity in registration with the second injection ports; and

a second relative position between the valve seat and slide locating the first sample storage cavity in registration with the first injection ports and the second sample storage cavity in registration with the second sample ports;

a first fluid protective shield in surrounding relationship with the first injection ports;

a second fluid protective shield in surrounding relationship with the second injection ports; and

means for effectively placing said first and second injection ports in series relationship with one another.

10. The double acting sampling valve as claimed in claim 9, wherein the first and second protective fluid shields include gutters formed in the interaction surface of the valve slide and valve seat with selected ones of said gutters being effectively spaced axially and transverse of the valve action axisalongside of first and second injection ports.

1 1. Chromatography apparatus of the type including a valve for introducing a sample mixture to a column, wherein the valve comprises:

first and second valve members mounted together for relative sliding movement into first and second positions and provided with smooth sliding surfaces for fluid sealing engagement;

said surface of one of said valve members being formed with a sample passage opening out into the region of sealing engagement between said two surfaces and providing communication to a quantity of sample mixture to be injected into the column for processing;

said surface of the other valve member being formed with a column passage opening out into the region of sliding engagement between said two surfaces and providing communication to the chromatographic column;

said sample passage being non-aligned with said column passage in said first valve position and aligned therewith in said second valve position, whereby to provide for injecting sample mixture into the column when in the second position;

a fluid protective shield comprising a fluid channel adapted to carry non-contaminating fluid in the region between said surfaces, said channel being located between said sample passage and said column passage when said valve is in said first position to serve as a barrier to prevent portions of the sample mixture from being drawn from said sample passage over to said column passage and thereby entering the column in said first position; and

means to supply non-contaminating fluid to one region of said fluid channel and to remove said nonof said one valve member and supplied with carrier 10 13. Apparatus as claimed in claim 11, wherein said surface of said other valve member is provided with both inlet and outlet ports for said column passage, said inlet port being connected to a source of carrier fluid, said outlet being connected to the column;

said sample passage being aligned with both said inlet and outlet when said valve is in said second position, whereby the sample mixture is forced by the incoming carrier fluid through the outlet port to the column.

14. Apparatus as claimed in claim 11, wherein said fluid protective shield comprises a continuous channel surrounding the sample passage.

15. Apparatus as claimed in claim 11, wherein the segment of said continuous channel which is between said sample passage and said column passage is located in said surface of said one valve member.

16. Apparatus as claimed in claim 11, wherein at least a portion of the remainder of said continuous channel is located in said surface of said other valve member.

17. Apparatus as claimed in claim 11, wherein said channel contains carrier fluid.

Claims

1. Chromatography apparatus including a sample valve for developing a metered amount of sample to be sent to the chromatographic column for analysis and comprising: a valve slide and a valve seat slidingly mounted to one another with said valve slide and valve seat being provided with smooth valve interaction surfaces for fluid sealing engagement during relative motion between the valve slide and seat; one of said interaction surfaces being provided with a sample storage passage means and the other interaction surface being provided with sample inlet and outlet ports located to align with the sample storage passage means at a first valve position; the other interaction surface being provided with injection inlet and outlet ports located to align with the sample storage passage means at a second valve position; and a fluid protective shield comprising a fluid channel between the interaction surfaces and positioned between the sample ports and the injection ports to serve as a barrier to prevent contamination of the fluid flowing to the column.

6. The sample valve as claimed in claim 1, wherein the fluid protective shield further includes a first pair of parallel gutters formed in the other interaction surface containing the injection ports and flankingly located adjacent thereto, a second pair of parallel gutters formed in the one interaction surface in overlapping relationship with the first pair of gutters to provide fluid flow communication between the gutters around the injection ports.

9. A double-acting sampling valve for a chromatographic instrument comprising: a valve slide and a valve seat slidingly mounted to one another with said seat and valve being provided with smooth valve interaction surfaces for fluid sealed engagement with relative motion between the valve slide and seat along a valve action axis; said valve seat being provided with first sample inlet and outlet ports, first injection inlet and outlet ports axially located from the first sample ports, second sample inlet and outlet ports located along the valve action axis and second injection inlet and outlet ports located between the second sample ports and the first injection ports; said valve slide being provided with a first sample storage cavity sized and located for alternate operative engagement between the first sample and injection ports and further provided with a second sample storage cavity sized and located for alternate operative engagement between the second sample and injection ports; a first relative position between the valve seat and slide locating the first sample storage cavity in registration with the first sample ports and the second sample storage cavity in registration with the second injection ports; and a second relative position between the valve seat and slide locating the first sample storage cavity in registration with the first injection ports and the second sample storage cavity in registration with the second sample ports; a first fluid protective shield in surrounding relationship with the first injection ports; a second fluid protective shield in surrounding relationship with the second injection ports; and means for effectively placing said first and second injection ports in series relationship with one another.

10. The double acting sampling valve as claimed in claim 9, wherein the first and second protective fluid shields include gutters formed in the interaction surface of the valve slide and valve seat with selected ones of said gutters being effectively spaced axially and transverse of the valve action axis alongside of first and second injection ports.

11. Chromatography apparatus of the type including a valve for introducing a sample mixture to a column, wherein the valve comprises: first and second valve members mounted together for relative sliding movement into first and second positions and provided with smooth sliding surfaces for fluid sealing engagement; said surface of one of said valve members being formed with a sample passage opening out into the region of sealing engagement between said two surfaces and providing communication to a quantity of sample mixture to be injected into the column for processing; said surface of the other valve member being formed with a column passage opening out into the region of sliding engagement between said two surfaces and providing communication to the chromatographic column; said sample passage being non-aligned with said column passage in said first valve position and aligned therewith in said second valve position, whereby to provide for injecting sample mixture into the column when in the second position; a fluid protective shield comprising a fluid channel adapted to carry non-contaminating fluid in the region between said surfaces, said channel being located between said sample passage and said column passage when said valve is in said first position to serve as a barrier to prevent portions of the sample mixture from being drawn from said sample passage over to said column passage and thereby entering the column in said first position; and means to supply non-contaminating fluid to one region of said fluid channel and to remove said non-contaminating fluid from another region of said fluid channel, the flow of said non-contaminating fluid between said two channel regions serving to intercept and carry away any sample fluid tending to leak bEtween said sliding surfaces from said sample passage opening to said column passage opening.

12. Apparatus as claimed in claim 11, wherein said fluid protective shield channel is located in said surface of said one valve member and supplied with carrier fluid.

13. Apparatus as claimed in claim 11, wherein said surface of said other valve member is provided with both inlet and outlet ports for said column passage, said inlet port being connected to a source of carrier fluid, said outlet being connected to the column; said sample passage being aligned with both said inlet and outlet ports when said valve is in said second position, whereby the sample mixture is forced by the incoming carrier fluid through the outlet port to the column.