US3537585A - Chromatographic separation system - Google Patents

Description

United States Patent 1 [72] Inventor JamesL.Waters 1,958,009 5/1934 McKee 138/30 Framiugham, Massachusetts 2,407,276 9/ 1 946 Hendel et al.... 138/26 [21] AppLNo. 738,259 3,185,211 5/1965 CrawfordetaL... 55/386X {221 Filed d i 238 OTHER REFERENCES 45] Patente ov. K

yryacos et al., Separation of Hydrogen, Oxygen, [73] Awgnee Ammes'lnc Nitrogen, Methane,and Carbon Monoxide by Gas Adsorption Framlngham, Massachusetts [54] CIIROMATOGRAPHIC SEPARATION SYSTEM 7 Clallus, 4 Drawing Flgs.

[52] US. Cl, 210/198, 2l0/349;55/197 [51] [Ill- Cl. B0111 15/08 [50] Field otSearch.L... 73/231; 55/67, 197, 386;210/31, 198, 349; 137/568; 138/26, 30

[56] References Cited UNITED STATES PATENTS 1,941,613 1/1934 McDonell 138/26 FLUID 2 2 SOURCE PUMP 7 Chromatography" Analytical Chemistry, Vol. 29, p787, May 1957.

Primary Examiner-J. L. DeCesare Attorney-Cesari and McKenna TUBE 22 24 DETECTOR Patehted Nov. 3, 1970 FIG. I

PUMP

. DETECTOR FLUID SOURCE FIG. 2"

time

FIG. 3

FIG, 4

INVENTOR. JAMES L. WATERS Maw ATTO R N EYS 1 CI'IROMATOGRAPIIIC SEPARATION SYSTEM BACKGROUND OF THE INVENTION I 1. Field of the Invention This invention relates to an improved chromatographic separation system. It relates more particularly to apparatus for delivering the carrier liquid and the sample liquid to the column in a substantially constant volume flow.

Chromatographic separators are used to separate the components of a liquid from one another to facilitate the identification of these components. The sample liquid, i.e. the fluid to be analyzed, may bea liquid or a gas. However, the present invention isdirected particularly to liquid systems.

The usual system comprises a chromatographic column which contains an absorbent packing. A pump connected to one end of the column pumps a mixture of a carrier and sam- -ple liquid into the column. The different components of the sample liquid traverse the column at different rates and therefore exit the column at different times. A detector connected to the other end of the column detects each sample component as it elutes from the column and thereby renders an analysis of the sample.

2. Description of the Prior Art The viscosity of the carrier liquid used to convey the sample through the column must be very low. Therefore, a conventional constant volume pump such as a gear pump cannot be used in these systems because the carrier leaks around the seals in thepump and theoutput from the pump to the column is, therefore,-erratic. v

The same requirement of a constant volume flow also militates against the use of a conventional reciprocating piston pumpwhose fluid output is delivered in" pulses. This is because the fluidpulses tend to pack down the material in the column,

thereby increasing its resistance to fluid flow. For several reasons, the usual antishock devices cannot be employed to smooth these pulses. First, their response time is relatively slow, with the result that variations still occur in the liquid flow to the column. Also,.most are not solvent, resistant. Other fluid pulse da'mpeners are relatively complicated and have various moving parts such as pistons, springs and the like which make them unsuitable for use in chromatography.

In applications involving low volumes and small fluid flows, satisfactory results are obtained from a bellows type of pump consisting of a stainless steel bellows sealed inside a pressure chamber. In those, the carrier liquid and the fluid to be analyzed are introduced into the bellows. Pressure is then applied to the chamber to compress the bellows, resulting in a constant volume flow of the carrier liquid and fluid to the chromatographic column.

However, the bellows type of pump cannot handle high volumes or large fluid flows. Moreover, it requires an external pressure source;

SUMMARY OF THE INVENTION Accordingly, it isan object of this invention to provide a chromatographic separation system which assures a uniform flow of carrier liquid to the chromatographic column.

A further object of the invention is to provide a chromatographic separation system having a fluid pulse dampener which smooths out variationsin the flow of I carrier liquid delivered to a chromatographic column.

A still further object of the invention is to provide a fluid pulse dampener for use n a chromatographic separation system which is relatively inexpensive to make and has a long useful life.

Another use of the invention is to provide a fluid pulse dampener which is relatively easy to clean and is self-purging.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims. a

Briefly, the present system employs a reciprocating piston pump to pump the carrier and sample liquids through a chro- 5 matographic column. A fluid pulse dampener smooths out variations in the flow of fluid delivered to the column so that the liquids are introduced into the column at a uniform rate.

The pulse dampener comprises a tube having a flexible, resilient wall. The tube, which thus has a pressure-expandable volume, is connected between the pump and the inlet end of the column; and a capillary restriction is disposed in the line between the tube and the column, Le. downstream from the tube. The resilient tube and the capillary restriction function together as a low-pass filter that largely prevents the cyclic variations in the pump outlet from reaching the chromatographic column. At the frequency of the pump, the tube provides a relatively low impedance in parallel with the capillary restriction and column and thus the cyclic component of the pump output is shunted by the tube. On the other hand, the tube has an infinite shunt impedance for the nonvarying (average) component of the pump output, and this component therefore passes entirely through the column.

Since the carrier and sample liquids are thus introduced into the column at a uniform rate, the column accurately separates the sample components from each other. These components elute from the exit end of the column and are identified by a suitable detector connected to receive them.

The fluid pulse dampener of the present system has low inertia so that it responds quickly to changes or pulsations in the fluid flow from the pump. This minimizes variations in the fluid flow to the column and minimizes errors in the chromatographic analysis.'Alsp the dampener herein has no movingparts except for the flexing tube wall, is small and relatively easy to make. Therefore, it is relatively inexpensive even though it is made out of a high quality material.

invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, in'which:

FIG. 1 is a block diagram with some parts in schematic form of a chromatographic separation system embodying the principles of my invention;

. DESCRIPTION OF TI-IEPREFERRED EMBODIMENTS Referring now to FIG. 1 of the drawing, the, sample, together with its carrier liquid, is drawn from a source 6 via a pipe 8 by a pump 10. Pump 10 is a positive displacement reciprocating pump so that the fluid flow from the pump periodically pulsates as shown by curve 11 in FIG. 2. Insofar as the present invention is concerned, the volume flow from the pump may be considered as essentially independent of the load imposed on the pump. Pump 10 pumps the fluid via a pipe 12 through a fluid pulse dampener indicated generally at 14 which smooths out the variations in fluid as indicated by the curve 15in FIG. 2.

Pulse dampener 14 delivers the fluid under conditions of substantially constant volume flow via a pipe 16 to a chromatographic column 18. Column 18 contains the usual bed 20 which sorbs the components of the fluid being analyzed. The different components of the fluid are sorbed and desorbed at different rates by the bed 20. Consequently, the different components traverse column 18'at different rates and thus elute from the column at'different times. The effluent from the column 18 is conducted by way of a pipe 22 to a detector 24 which senses each component as it elutes from the column.

Still referring to FIG. 1, pulsedampener 14 comprises a tube 26 connectedv to receive the output from pump 10. Tube 26 has a flexible and resilient wall. Also, it has'a noncircular, herein generally elliptical, cross section, as seen in FIG. 3. In the illustrated embodiment of the invention, tube 26 is a thinwalled stainless steel tube. v

A capillary restriction indicated at 30 is situated in the line between tube 26 and column 18. In practice, restriction 30 may simply be a constriction in pipe 16 leading from tube 26 to column 18 or in the exit end of tube 26. Actually, it may be located anywhere downstream from the tube 26, e.g. at the outlet end of the column 18; however, the illustrated location is generally more convenient.

The characteristics of tube 26 are such that an increase'in the fluid pressure applied to the tube causes the tube to round out". That is, its cross section distorts toward a generally circular shape as seen by the dotted line 26a in FIG. 3. This increases its volume somewhat. When the pressure of the fluid in tube 26 subsides, the tube returns toward its normal unstressed condition as seen in FIG. 3 wherein it has a generally elliptical cross section and a smaller volume.

With this arrangement, the tube 26 and restriction 30 function much like an electrical R-C filter driven by a constant current source. The restriction 30 and column 18 are analogous to series-connected resistances and the tube 26 is analogous to a capacitor connected in parallel with these resistances. The compliance of the tube is sufficiently great to provide a reactance that is much less than the combined resistance of the restriction and column at the frequency of the pump 10. Accordingly, the pulsations from the pump are, in effect, absorbed by the tube 26. r I

From this, it will be apparent that the restriction 30 could be eliminated entirely if the column 18 were large enough to have in itself sufficient resistance to flow. Ordinarily, however, the resistance of the column is less than that required for a highly efficient pulse-dampening system.

Also, it should be appreciated that substantially the same result obtains when a simple elastic tube of nonreactive material such as Teflon plastic is used in lieu of tube 26.

FIG. 4 shows a modified pulse dampener 14a wherein one end of an arcuate bourdon tube 26b is connected to pipe 12 ahead of restriction 30. The other end of tube 26b is closed. The FIG. 4 dampener operates in much the same way as the one illustrated in FIG. 1. That is, the fluid pulses in pipe 12 are largely absorbed by tube 26b whose shape resiliently changes in response to pressure changes. Specifically, tube 26b being curved tends to straighten out when the fluid pressure inside it increases and to resume its FIG.. 4 shape between these fluid pulses.

It is, of course, also feasible to'employ two or more of the FIG. 1 or FIG. 2 dampeners in series to obtain additionalfiltering action.

The pulse dampener 14 in FIG. 1, having all its components directly in the line to the column, is greatly advantaged over its FIG. 4 counterpart as well as conventional pulse dampeners because it does not have to be cleaned between runs of dif-, ferent samples. That is, the operator can change from one sample to another without even interrupting the process because the flow of the second sample through tubes 12, 16 and 26 quickly purges them of all traces of the first sample. Thus, after a very short transition time, the system can accurately analyze the second liquid.

This is a very desirable feature because in some applications one may wish to run several samples through the system one after the other to yield an output which is in the form of definite steps demarking the different samples. The FIG. 1 apparatus is ableto accomplish this for the reasons just mentioned. Other comparable devices, on the other hand, having elements which are not in the line to the column, are not satisfactory for this purpose because these elements are not cleaned quickly enough. There is carryover from one sample to the next with the result that the output from the system does not have the desired pronounced steps.

It will be seen from the foregoing, then, that the illustrated chromatographic separation system employing my pulse dampener substantially eliminates the likelihood of fluid pulses causing the material in bed 20 to pack down. Accordingly, these systems can now use conventional, reliable reciprocating pumps without adversely affecting the I flow of fluid through the column. Moreover, the pul se dampener disclosed herein is small, lightweight and relatively easy to make. In addition, the dampener has essentially no moving parts and can be fabricated easily out of high quality metals or materials which must be used in systems of this type. Finally, the pulse dampener of FIG. 1 is very easy to clean between runs of different fluids and both types can generally be maintained by relatively unskilled personnel.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Iclaim:

I. A chromatographic separation system comprising:

A. a chromatographic column;

B. a pump for pumping carrier fluid toward said column;

and

C. means for dampening out the pulses, in the fluid said dampening means comprising:

1. a fluid restriction in the flow path from said pump; and

2. a flexible, resilient tube having a noncircular cross section connected between said pump and said restriction for absorbing fluid pressure fluctuations ahead of said restriction so that said pulses are averaged out before the fluid is introduced into said column.

2. In a chromatographic separation system having a chromatography column anda source of carrier fluid, the improvement which comprises:

B. a fluid restriction connected between said pump and said column; and

a flexible, resilient, out-of-round tube connected between said pump and said restriction, said tube flexing toward a round condition in response to pressure, fluctuations in said fluid.

3. Apparatus as defined in claim 2 andfurther including a detector connected to receive the effluent from said column.

4. A system as defined in claim 2 wherein said tube is open at both ends and connected directly in the line between said pump and said restriction.

5. A system as defined in claim" 2 wherein said tube is a bourdon tube having its open end connected between said pump and said column.

6. A chromatographic separation system comprising:

A. achromatographic column;

B. a pump for pumping carrier fluid toward said column;

and

C. means for dampening out pulses in the fluid, said dampening means comprising a flexible, resilient tube having a noncircularcross section connected between said pump and said column and a fluid restriction downstream from said tube for absorbing fluid pressure fluctuationsso that said pulses are averaged out before the fluid is introduced into said column.

7. Apparatus as defined in claim 6 and further including a detector connected to receive the effluent from said column.

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