US2963898A - Gas chromatography unit - Google Patents

Description

Dec. 13, 1960 M. s. REYNOLDS ETAL 2,963,898

GAS CHROMATOGRAPHY UNIT Filed Aug. 27, 1957 5 Sheets-Sheet 1 fig 9.1 3|

Inve nto rs Man-ch19 5. Ret nolds iflfth'ut 31. Na kata.

Dec. 13, 1960 M. s. REYNOLDS ETAL 2,963,898

GAS CHROMATOGRAPHY UNIT Filed Aug. 27, 195'. 5 Sheets-Sheet 2 inverrto rs Manning 5. Regs-1o Ids Dec. 13, 1960 M. s. REYNOLDS ETAL 2,963,898

GAS CHROMATOGRAPHY UNIT Filed Aug. 27, 1957 5 Sheets-Sheet 3 r "HM 1111/ en l'o rs Manning S- Reynolds Arthur H Nakata.

Dec. 13, 1960 M. s. REYNOLDS EI'AL 2,963,898

GAS CHROMATOGRAPHY UNIT Filed Aug. 27, 1957 5 Sheets-Sheet 4 Fig- Inventor Manning 5. Regnolds Arfhur Tl No Kata.

B JIM, 5m

ovnegs Unit es Patent r GAS CHROMATOGRAPHY UNIT Manning S. Reynolds and Arthur H. Nakata, Chicago,

111., assignors to Central Scientific Company, a corporation of Illinois Filed Aug. 27, 1957, Ser. No. 680,463

2 Claims. (Cl. 7323) This invention is concerned with gas chromatography apparatus and has for its principal object the provision of a compact, economically constructed unit for general laboratory use that is adaptable, without modification, to various types and ranges of quantitative and/or qualitative analyses and measurements, that is accurate and reliable, that provides maximum operator convenience, and that provides ready access for exchanging or replacing various parts of the apparatus.

Generally speaking, in the present invention, a basic oven construction is arranged to receive the vital parts of a gas chromatograph, with these parts being interconnected as a complete subassembly that functions as a complete setup to permit convenient testing prior to installation. After testing, the subassembly may be handled as a one-piece unit for ease of mounting in the oven. The necessary external controls are brought through the oven walls and secured to the internally mounted subassembly. All control gauges and dials necessary for operation are also brought through the oven walls and are accessible externally. All of this is done in a manner compatible with the important requirement of providing an oven arrangement that produces a properly regulated, uniform heating of the various parts of the chromatograph system.

Other objects and advantages of the invention will become apparent as the description proceeds.

In the accompanying drawings forming a part of this specification and in which like numerals are employed to designate like parts throughout the same,

Fig. l is a front elevational view of a chromatograph arrangement, with parts of the front wall of the oven broken away to better illustrate the arrangement;

Fig. 2 is a side elevational view of the apparatus, with parts of the side wall of the oven broken away;

Fig. 3 is a top plan view of the oven of Figs. 1 and 2;

Fig. 4 is a top plan view of a packaged subassembly prior to its insertion in the oven;

Fig. 5 is a front sectional view of the packaged subassembly taken along the line 5-5 of Fig. 4;

Fig. 6 is a sectional view illustrating the construction of the inlet system for liquid samples;

Fig. 7 is a sectional view of the gas sampling control valve employed in the invention;

Fig. 8 is a sectional view taken on the line 8-8 of Fig. 7; and

Figs. 9 and 10 aresectional views taken on the lines 9-9 and 1010, respectively, of Fig. 8.

General arrangement The purpose of gas chromatography is to separate the various components of liquid or gas mixtures for separate measurement and identification, and gas chromatography permits a quick and eflicient arrangement for making quantitative and/ or qualitative determinations on various types of unknown samples. In the case of gas samples, the sample volume may be on the order of /2 cc., while in the case of liquid samples, the sample 2,963,895 Patented Dec. 13, 1960 ICE volume may be on the order of .01 cc.; and this, in combination with the speed, accuracy, and efliciency inherent in gas chromatography, has made it one of the most rapidly-developing fields in present day technology. While much has been done in laboratories in recent years in researching, improving, and extending gas chromatography and while the general principles of the system have long been known, there has existed a real need for a ruggedly constructed, compact, reliable, and economical unit for general laboratory use. The present invention seeks to fill this need and, in carrying out its aims, has provided a compact oven construction that includes all of the components necessary to the system with the single exception of the recorder, so that the unit may conveniently be mounted on a laboratory bench for external connection to any appropriate type of recording device.

According to the present invention, the basic components of a chromatograph system are mounted in an oven, designated generally at 20, that includes insulated top, bottom, side, front, and rear walls, designated respectively as 21, 22, 23, 24 and 25, which form a generally cylindrical, horizontally extending oven chamber 26, with the various walls including the necessary electrical heating elements and with the front wall 24 being mounted on hinges 27 and provided with a handle 28 to provide a hinged access door for the oven compartment. The oven is mounted on a hollow base, designated generally as 29, that conveniently houses the auxiliary control equipment for the active parts of the system which are disposed in the oven chamber itself.

One of the basic components of the chromatograph system is an elongated column 30, which is here shown in the form of a tightly-wound helix. The column is constructed of an elongated, formable, aluminum tube to facilitate its winding; and the tube is substantially filled with any conventional matrix material, which may consist, for example, of porous firebrick mixed with a stationary liquid phase that coats the firebrick. Of course, various column-packing materials may be employed, depending upon the type of analysis that is to be made, and this aspect of the system forms no part of the present invention. It is believed to be unique, however, to employ aluminum tubing as the column-forming medium since aluminum resists oxidation, a particular problem in earlier devices in view of the extended exposure of the column to high oven temperatures, which frequently run on the order of 200 C. or more.

In gas chormatography, a steady flow of carrier gas, such as helium or argon, together with a sample to be analyzed, is passed through the column in which the sample is separated into its components. A property of the gas mixture coming out of the column, such as thermal conductivity, is then detected with a detector cell. The data obtained are then interpreted in quantitative and qualitative terms. The carrier gas is introduced through a pressure-regulating valve 31, passes through the reference side of detector cell 32, and through the column 30 and the sample side of detector cell 32, finallyemerging through a flowmeter 33 that extends upwardly through an opening 34 in the top wall 21. In the present system, the flow path, when maintained at any given constant temperature, does present a constant impedance to gas flow. To provide constant gas flow rates, it is only necessary to apply the carrier gas at a constant pressure at the inlet to the system; and for this purpose, a precision-type pressure-regulating valve 31 is employed. As is conventional, the unknown sample is introduced at the front of the column and is carried through the column by the flow of the carrier gas under the influence of the oven.

In the case of a liquid sample, the apparatus is arranged to accommodate the needle of a syringe of the type shown in co-pending application, Serial No; 671,634, filed July 12, 1957, now Patent No. 2,855,928, the disclosure of which, to the extentit is not inconsistent herewith, is specifically incorporated by reference, and for this purpose a stainless steel guide tube 35 extends through the top wall 21 of the oven to accommodate the needle, which is movable downwardly through the tube to pierce a self sealing liquid inlet valve 36 to inject the sample into the stream of carrier gas at the front of the'column 30. s

It is generally desirable to maintain uniform heating of all parts of the system, and it is particularly important that the region of the inlet for the unknown liquid sample be maintained at the appropriate temperature for, the particular sample in orderto vaporize the entire sample immediately and minimize diffusion of the sample vapor and carrier gas. A practical arrangement for most effectively insulating the liquid sample inlet is represented by the small-bored, thin-walled, stainless steel guide tube which is brought through the oven wall to accommodate and guide the syringe injector while limiting heat loss to the outside. The stainless steel-tube may readily be machine-threaded for connection to the inlet, and it withstands engagement by a wrench for tightening the connection. These are practical considerations that preclude the use of a glass tube which would necessarily require more elaborate connection arrangements.

For gas samples, the apparatus includes a gas sampling valve 38 that permits a measured quantity of a gas sample to be introduced into the stream of carrier gas immediately prior to its passing through the column 30. The inlet'and outlet fittings for the gassample are shown at 39 and 40, respectively, in Fig. 3, and the external handle for operating the gas sampling yalve is'designated 41. The plumbing connections for the gas sample valve are described in detail hereafter.

The detector cell 32 that is illustrated herein is Model No. 9285, made, and sold by the Gow-Mac Instrument Co., of Madison, New Jersey, and it is a thermo-conduetivity comparison type detector cell that includes an electrical bridge arrangement of resistance elements, the power supply for which is arranged to convert the usual 110-volt, 60-cycle supply to 6 volts D.C., and the controls for which are shown on the console panel at 42 and 43, the necessary connection wires being run between the detector cell 32 and-the controls in thebase through a suitable sheath 46 of woven glass fibers. The console panel also includes binding posts 44 for connection to any suitable recorder, and a manual switch 45 'is preferably provided for reversing polarity between therecorder and the detector cell. 7

For the usual analyses,-the oven temperature require ments may range from 25 C. to 200 C. An important considerationin achieving accurately reproducible analyses is the maintenance of a constant and uniform temperature in the oven chamber 26, and, accordingly, a 4-inch fan 47 is mounted at the bottom of the oven chamber for rotation about a vertical axis to maintain even heat distribution throughout the oven chamber, a portion of the heated air being forced out the opening 34 in the top wall of the oven. The fan 47 is driven by a motor 48 that is conveniently mounted in the hollow base 29, and a motor-cooling fan 49 is also mounted in the base. The fan 49 cools motor 48 and generally maintains the base chamber at reasonable operating temperatures. The controls for regulating the oven temperature consist of a general adjustment 51 and a fine, or Vernier, adjustment 52, both of which are mounted on the console panel. Their construction, connection and operation are-well known to those familiar with the oven art.

Finally, the apparatus includes a chimney tube 54, of transparent heat-resistant material such as glass, which extends upwardly from the opening 34 to surround the flowmeter 33 and continuously subject it to the hot air that emerges from the oven chamber through opening 34.

4 Thus the flowmeter is not only made conveniently visible to the operator, but it is maintained substantially at oven temperature, an important feature in properly controlling the present apparatus. This feature is particularly important in the case of liquid samples, which might tend to condense and clog the flowmeter were it not maintained at an appropriately high temperature. A thermometer 55 is also mounted in the chimney with its sensing bulb 56 extending to approximately the center of the oven (see Fig. 2).

In testing unknown samples with the present appparatus, it is important to maintain exact uniform temperatures and flow rates, and the present invention depends upon adjustable'controls that may be set according to the indications on reliabletypes of thermometers and fiowmeters. This permits accurate regulation of the gasflow rates without depending upon expensive, built-in, pro-calibrated control arrangements that are so, frequently subject to loss of accuracy and that usually require frequent maintenance. According to the present invention, the required indicators are brought through the transparent chimney tube 54 to make them conveniently available to the operator without impairing their-accuracy and without compromising other phases of the construction. The arrangement has obvious advantages over constructions'which dispose these elements entirely within the oven so that either the oven door must be opened to check their readings or one of the oven walls must be provided with a glass viewing panel, which not only decreases the insulation characteristics of the oven, but also becomes dangerously hot.

As a general guide to an appreciation of the compactness and convenience of the apparatus, one typical constructional form is embodied in a unit that is 19 inches wide, 21 inches high, and 15 inches deep, and that weighs approximately 58 lbs.

Specific description There arenumerous specific constructional features which can bepointed to as being primarily responsible for the many advantages that are offered by thepresent device. It is helpful to an'understanding of the detailed construction to first trace out the flow path of the incoming carrier gas which, after passing through the pressure-regulated valve 31, flows successively through the following, readily identifiable plumbing connections: inlet T fitting'100 (Fig. l); vertical-tube 101; elbow 102; through one half of detectorcell'32rfitting 103; tubing section 104; inlet elbow fitting 105 of the gas sampling valve 38; outlet fitting 106 of the gas sampling valve; tubing 107; and through the horizontal leg of an inverted T fitting 108, the upper end of which cooperates with the self-sealing inlet disc type valve 36 through which liquid samples are injected;- tubing 109; fitting 110 to the column 30; and out the column through fitting 111; then through tubing 112 to fitting 113, which may receive 'a through-loop 114, as shown in Fig. 1, or which, alternatively, may receive a tight-wound, helical column, such as shown at 30; through the loop or column to fitting 115; tubing section 116; and an inlet fitting 117 of the detector cell; through the other half of the detector cell 32; and out the outlet fitting 118, through the tubing 119 and fitting assembly 120 which-receives a specially formed tubular section 121 (Fig. 2) on which the fiowmeter 33 is mounted. It will be noted that the circuit for the car: rier gas passes through boththe gas sampling valve and the liquid inlet system, which are arranged for independent usage so that eitherone may be used without having to rearrange'or reset-the system in any way. I

The arrangement for injecting the inlet samples is better shown inFig.,6 wherein the vertical stub 123 of t e in er d T as embly 108 is in threaded engagement in the socket,124 carried at the lower end of the stainless steelrtubing, with the valve disc 36 disposed be: tween the stub 12 3 and socket 124 to isolate the region of the carrier gas chamber that is defined by the T connector 108 from the stainless steel tube 35, which, of course, is open to the atmosphere. The valve disc 36 is preferably of silicone rubber and readily withstands the high pressures and high temperatures to which it is subjected. The disc is of approximately the same diameter as the socket 124, and as it is compressed axially in the region of its outer periphery, radially, inwardly-directed pressures are set up to place the center of the disc under compression, as evidenced by the bulging center region, and develop a self-sealing action. The disc is, preferably, on the order of of an inch in diameter and A; of an inch thick, and liquid samples are introduced by piercing the disc with the needle of a syringe, the needle being inserted through the top end of the stainless steel tubing and guided by the walls of this tube to insure proper puncturing. The inside diameter of the tubing is on the order of 51 of an inch.

It is important to an accurate and reliable device that the quantity of the liquid sample be accurate and repeatable and that the entire sample be introduced, vaporized, and swept away by the carrier gas substantially simultaneously. Towards this end, a wad of glass wool 125 is located in the fitting 108 to extend across the main gas stream and provide a wiping medium that removes any last drop of sample that may otherwise tend to cling to the needle of the syringe. It will be apparent that the silicone disc maintains a continuous seal, even at the time of insertion and removal of the needle; and though it may be punctured numerous times, the continuous radial pressures prevent the developing of an open slit as usually results when the punctures begin to overlap one another.

The gas sampling valve is also arranged to facilitate the introduction of unknown gas samples and to permit of completely isolating the regular carrier gas circuit from the gas sample circuit at all times. The gas sample circuit itself may be traced from the external gas inlet 39, through the top Wall 21 of the oven, to fitting 130, through elbow 131, and tubing 132 which is bent around to enter the gas sampling valve 38 on the left-hand side at the bottom through fitting 133 (see Fig. 5). After passing through the valve 38, the sample gas passes through fitting 134, tubing section 135, elbow 136, fitting 137, through the oven wall, and out the external gas outlet 40;

The gas sampling valve of the invention comprises a block-shaped valve body 140 having a downwardly-tapering vertical bore 141 in which is received a tapered plug valve 142 for rotation about a vertical axis. The plug has an upper extension 143 that passes through the top Wall 21 of the oven for attachment to the actuating handle 41. The valve body includes inlet and outlet sockets, 144 and 145, respectively (Fig. 9), for the carrier gas, with both of these sockets communicating with the central bore 141 and inlet and outlet sockets, 146 and 147, respectively (Fig. 10), for the gas sample, which also communicate with the bore 141 at a lower elevation. The valve plug is formed on its opposite sides with sectorshaped, passage-forming recesses, 148 and 149, in the region of the carrier gas sockets, and 150 and 151 in the region of the sample gas sockets, with the path-forming recesses at the level of the carrier gas sockets extending at right angles to the path-forming recesses at the level of the sample gas sockets. With the plug in the position shown, the carrier gas comes in the inlet socket 144 directly through recess 148 and out the outlet socket 145, while the sample gas, if its circuit is connected, comes through the inlet socket 146, through the recess 150 and up through the external loop 152, back to the bore through recess 149 and down through the internal passage 153, and finally back through recess 151 and the outlet socket 147. With the gas sample flowing in this manner, the handle 41 is actuated to turn the valve plug 142 90 counterclockwise, as viewed in Figs. 9 and 10,

and establish a new relationship of parts whereby the carrier gas will enter through socket 144, recess 149, down through internal passage 153 to recess 150, and up through the external loop 152 to recess 148 and, finally, out the carrier gas outlet socket 145. It will be seen, therefore, that the gas sample that had previously been trapped in the external loop 152 and the internal bore 153, as well as the sample trapped in recesses 149 and 150, will be introduced into and swept along by the stream of carrier gas. It is important to note that the reduced portions of the valve plug which are defined by the recesses are larger than the ports which they control so that, in every case, as the valve is rotated to open one port and close another, the port that is to be closed will seal off completely before the port that is to be opened is exposed. This prevents interflow between the carrier and sample gas streams and insures trapping and transfer of the same volume of sample each time, an important feature to an accurate device. The arrangement illustrated is particularly advantageous from a cost standpoint and it also achieves the desirable goals of minimizing the actual volume of gas sample that may be introduced and this should, preferably, be on the order of one cc. or less, depending upon the particular sample. The use of the direct internal passage 153 in the valve block permits the sampling arangement to be of minimum capacity, while the use of the demountable external loop permits varying the actual volume of the samples as desired.

All of these various parts of the system are connected in the form of a single, compact, subassembly that is readily inserted into the oven and connected to the neces sary external controls. In accomplishing this, regard is had to the necessity of realizing uniform heating of the entire system and regard is also had to providing convenient access to the various parts of the system to permit of interchanging columns, as is so frequently necessary, and also to permit interchanging gas sample loops as well as to facilitate repair or replacement of various parts of the device.

Accordingly, a novel framing arrangement has been worked out to receive the parts in rigid connection and also to provide necessary access and circulation paths. The framing consists of front and rear trapezoidallyshaped channel sections 155 and 156, respectively, arranged in parallel, spaced-apart relationship with their respective upper flanges 157 and 158 interconnected by a perforated top plate 159 through which the several external fittings extend. Finally, the lower flanges 160 and 161, respectively, of the front and rear channel sections support a depending, U-shaped platform 162 on which the detector cell 32 is secured. The bottom flange 169 of the front channel also reinforces various intermediate points in the system and, towards this end, fittings 110, 111, 113, and 115 are all anchored to this flange. The various inlet and outlet fittings 108, 120, 130, and 137, as well as the gas sampling valve itself, are anchored to the top panel.

The front panel is also formed with apertures 163 and 164, respectively, in the region of the liquid inlet and in the region of the gas sampling valve, and these apertures, together with the four perforations 165 in the top plate, improve the internal heat circulation and particularly maintain the sample inlets at the general oven temperature and this, of course, is desirable since the samples should be introduced at oven temperature. The trapezoidal shape of the front and rear channels is selected to conform to the shape of the oven, as is apparent in Fig. 1.

As pointed up briefly hereinbefore, the loop 114 can be replaced with a column so that two columns may be operated in series. This is frequently desired, and such flexibility is important in a general laboratory instrument. In addition, the columns are secured by quick-connector assemblies which are released merely by pulling downwardly on the knurled collars 166 and which are rein- .serted simply by forcing them upwardly into the connecmounted withits' central passage extending vertically to aid' general circ'ulation within the oven and, particularly, .tosinsure thatall parts of the column are similarly and uniformly heated. This vertical position also permits ready access tothe connection fittings for the column. In the completed arrangement, aperforated plate '167 is mounted in the oven as a guard and air baffle for the fan 47. The completed subassembly of Figs. 4 and'5 is inserted at the top of the oven with the ends of the channels riding on the usual horizontal rails 168 provided at the sides of the oven. The columns may beconnected either before or after inserting the assembly into. the oven. Finally,'the external fittingsare passed through the top wall of the oven. and connected to the subassembly, which is then fixed-in position by suitable clamping facilities 169 which engage the rails.

It is an important advantage that the subassembly of Figs. 4 and 5, when provided with the desired column arrangement, presents a fully operative system that may be completely tested for proper operation prior to mounting it within the ovens.

It should be undrestood that the description of the preferred form of the invention is for the purpose of complying with section 112 of Title 35 of the US. Code, and that the appended claims should be construed as broadly as the prior art will permit.

We claim:

1. In agas chromatography system that includes an oven having a heating chamber surrounded by insulated walls, a source of carrier gas external of said chamber, and a carrier gas circuit mounted in said chamber and connected to said source; the improvement wherein one of the walls of said oven is formed with an opening, said carrier gas circuit includes a flowmeter that extends through said openingvand is visible externally, a chimney of transparent material iszmounted on said one-oven wall and-extends :outwardlyfi therefrom to surround zsaid .flowmeter and maintain said'flowmeten substantially .at the temperature of said even, and-isaid' source of carrier gas includes an externally .manipulable iva'lve for regulating the rate of.flow.o; carrier gas through -said carrier gas circuit in accordance :with. indications on said flowmeter.

;2. In .a gas chromatography system that includes an oven 'having a. heating :chamber. surrounded by insulated 'walls, a sourceio'f carrier gasexternal of said chamber, and a carrier gas..circuit mounted in said chamber and .connectedto said..source;-the improvement wherein said oven hasits top wall formed with a vertical opening, said carrier gas circuit includes a fiowmeter extending vertically through gsaid opening for external viewing, a chimney of transparent material is mounted on said top wall and extends vertically therefrom to surround said flowmeter and maintain:;said *flowmeter substantially at the temperature of said oven, and said source of carrier gas includes-an external-1y :manipulable valve for regulating the rate of flow'of carrier gas through said carrier :gas circuit in accordance -,with indications on said flowmeter.

References Cited in the file of this patent UNITED STATES PATENTS Harvey May 6, 1958 OTHER REFERENCES

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