Apparatus For Chromatographic Separations

Abstract

The subject chromatographic column employs certain excitation means to alter the sorption of a sample passing through a sorbent contained within the column to better effect separation of the various components of the sample. These excitation means include a geometric curvature of the central cavity of the column, or a voltage gradient established within the cavity between the column wall which defines the cavity and an electrically isolated wire extending along the longitudinal axis of the cavity, or a combination of the two. The columns can be housed in series within composite blocks and these blocks can be stacked to permit columns of substantial length within a confined space.

Description

This invention relates to chromatography and, more particularly, to the chromatographic column.

Basically, chromatography consists in passing a sample mixture through a sorbent contained within the chromatographic column, thus providing a two-phase system. In gas chromatography, a liquid sample is vaporized and sent through the column as a gas. Advantage is taken of the different equilibria which exist between the two phases to separate the components of the sample as a result of the different equilibrium constants thereof. The sample mixture is normally passed through the column with the aid of a carrier gas. The various components of the sample form separate bands in the carrier and as these separate bands leave the column, they are recorded as a function of time by a suitable detector.

A number of drawbacks exist with present chromatographic systems. Strongly retained components travel very slowly or, in some cases, do not move at all within the column. This problem is combated by using temperature programming, but many samples are heat labile and are adversely affected as a result thereof. Conventional chromatographic processes are generally adaptable only to small sample separation or analysis and are not suitable for large volumes of solutions. Existing chromatographic systems include chromatographic columns of substantial length to affect adequate separations and, as a result thereof, a substantial space is necessary to accommodate elongated chromatographic columns.

My invention overcomes the problems of strongly retained compounds, slow elution, partial resolution of compounds and unsuitable conditions of flow rate of the carrier fluid. In addition, my chromatographic column permits normally heat reactive labile compounds to be chromatographed. My chromatographic column also permits analysis of large, as well as small, sample mixtures. My invention is a chromatographic column which enhances the resolution of fluid mixtures by controlling individually or in combination the variables of column geometry and voltage gradients within the column. The geometry can be controlled by using curved symmetrical surfaces to define the central cavity and which increase in cross section inwardly from both the inlet and outlet ends thereof. The voltage gradient is established within the cavity between an electrically isolated wire extending along the longitudinal axis of the cavity and the wall of the column which defines the cavity.

In the accompanying drawings, I have shown my presently preferred embodiments of my invention in which:

FIG. 1 is a section through a geometrically shaped chromatographic column;

FIG. 2 is a section through a chromatographic column having a plurality of geometric shapes connected in series;

FIG. 3 is a section through a standard chromatographic column having a conducting wire extending therethrough;

FIG. 4 is a section through a chromatographic column similar to that depicted in FIG. 1 but including a conducting wire extending therethrough;

FIG. 5 is an isometric of a simplified composite chromatographic block;

FIG. 6 is an exploded view of a modified composite block;

FIG. 7 is a plan view of the central template cavity containing layer illustrated in FIG. 6; and

FIG. 8 is a plan view of the valve containing metal conducting layer of FIG. 6.

It is recognized theory in gas chromatography that specific forces, electrochemical in nature, are involved in obtaining separation between different components of a sample. These various electrochemical forces determine the differential solubilities and, therefore, the resultant separation of the compounds. The combined effects of these various electrochemical forces are expressed by a partition coefficient (index of separation) which is normally fixed throughout a chromatographic determination. My invention alters these electrochemical forces by adulterating the environment of the sorbent and solute and, therefore, changes the sorptive characteristics of the sample passing through the cavity.

The sample to be analyzed is passed through a sorbent in the gaseous state by means of a carrier gas. The sorbent, commonly referred to as "substrate" or "packing material," is a porous substance which must sorb the components of mixtures selectively and reversibly.

The chromatographic column illustrated in FIG. 1 utilizes a geometric curved shape to alter the sorbent environment of a sample passing therethrough. That column, generally designated 10, consists of a geometric curved surface 12 which defines a central cavity 14. Curved surface 12 increases in cross section inwardly from both the inlet end 16 and the outlet end 18. The cavity 14 defined thereby is symmetrical about all the axes and the particular curve illustrated is defined by the equation Y = e.sup.-.sup.kx . It is necessary that the cavity 14 be symmetrical at least about the longitudinal axis of the cavity.

Because of the curvature of the cavity 14, the affinity of the sorbent within the cavity for the sample passing through the cavity is not only a function of two dimensional distance traveled through the column, but is also a function of discreet three dimensional volume bands. This differing path length causes an obvious and discreet change in retention time and can be visualized as concentric doughnut shapes forming in and passing through the column. The components having the least affinity for the sorbent will pass along the longitudinal axes of the cavity 14 and those components having greater affinities for the sorbent will eddy out into the increased space provided by the curvature of the cavity 14 to increase the retention time for that particular component within the cavity and, thus, assist in separation of the components leaving the exit end 18 of the chromatographic column 10. The decreasing cross section approaching the outlet end 18 further accentuates the component separation by exaggerating one volume band from another.

Not only can the specific curvature be changed for different systems, but similar columns 10 can be connected in series as illustrated in FIG. 2. There, two cavities 14 are connected in series with the outlet end 18 of the first cavity coaxially aligned and cooperating with the inlet end 16 of the second cavity. This can be accomplished within a single unit by connecting two or more separate units in axial alignment.

The electrochemical nature of the sorbent and solute can also be altered by effecting a voltage gradient within the cavity. The chromatographic column 10 having a standard cylindrical central cavity 20 and such a voltage gradient is illustrated in FIG. 3. The cavity 20 is defined by a conducting metal wall 22 such as aluminum or copper. A thin copper wire 24 extends along the longitudinal axis of cavity 20 and is electrically isolated from wall 22 by standard insulating means (e.g. asbestos or Teflon gaskets) 26. The copper wire 24 is connected to a heavy duty D.C. potentiometer, not shown, and the anode of the potententiometer is connected to the block or wall 22. The wire 24, therefore, is in the geometric center of the cavity 20 running its entire length and is in contact solely with the sorbent 28. The voltage gradient is then established between the wire 24 and the wall 22 within the cavity 20. The wire can also be a thin elongated bar of an electrical conducting material such as carbon.

The geometric and voltage gradient techniques of altering the affinity of a sample and a sorbent can be combined as illustrated in FIG. 4. There, column 10 includes both a geometrically shaped cavity 14' and an electrically isolated wire 24'. Wire 24' which extends along the longitudinal axis of cavity 14' is electrically isolated from wall 12', which defines the cavity 14', by standard insulating means 26'. In this embodiment not only is there a combination of the geometrical shape effect and voltage gradient effect, but the latter is compounded by the former. That is, since the cavity 14' is increasing in cross section inwardly from both the inlet end 16' and the outlet end 18', the voltage gradient within the cavity 14' is not a constant. Since the wire 24' extends along the geometric center of the cavity 14', the voltage gradient effect is produced with maximum readings at the column center and progressively diminishing readings in both directions proportional to the varying distances between the wall anode defining the cavity curvature and the wire 24'.

The above principles may be embodied in a variety of different ways, in addition to the single column or coaxially aligned columns depicted hereinabove.

FIG. 5 illustrates a simple composite block 30 formed of two layers 32 and 34, respectively. Each layer contains a number of parallel cavities 36 recessed therein. These cavities 36 are connected in series by crossovers 38 also recessed within each layer. When the two layers 32 and 34 are sealably joined in gas tight relationship, the recessed cavities 36 of each layer align and cooperate to form the cavities and column for the sorbent. An inlet 40 extends through the upper layer 32 and connects with the first cavity 36 of the series and an outlet 42 connects with the end of the last cavity in the series. These cavities 36 can be standard, or can incorporate one of both of the geometric and voltage gradient principles discussed hereinbefore. In addition, these composite blocks 30 can be stacked to form an even longer resultant column. To form such a stack of composite blocks, it is necessary to have inlet and outlet means of composite block 32 positioned in such a manner that in stacked relationship the outlet of a first composite block communicates with the inlet of an adjacent composite block.

The composite block arrangement can be further modified to facilitate the development of the requisite voltage gradients within the cavities, FIGS. 6-8.

The composite block 30 disclosed therein includes a plurality of different layers joined in assembled relationship to form the chromatographic column. The top and bottom layers 42 and 44, respectively, are metal blocks such as aluminum. These blocks are normally placed in a heated environment and it is necessary to have a somewhat heat resistant material. In addition, the blocks must withstand substantial torque-bolting to form noncrimped gas tight seals of the various other layers sandwiched therebetween. An electrical insulating layer 46 made of a material such as asbestos is positioned adjacent the lower layer 44. Adjacent the asbestos layer 46 is a copper plate 48 which forms one of the common poles for the voltage gradient. Adjacent the copper plate 48 is a Teflon layer 50 and adjacent layer 50, a second Teflon layer 52. These two Teflon layers, 50 and 52, form the template for the chromatographic cavities 54. Each Teflon layer, 50 and 52, includes a plurality of cavities 54 which extend clear through the thickness of each layer, FIG. 7. These cavities 54 are in parallel relationship and can be the cylindrical type cavity or the geometrically shaped curvature type previously discussed, or a combination of the two. Both types of cavities are illustrated in FIGS. 6 and 7 for ease of presentation.

The two Teflon layers 52 and 50, are made separately to facilitate the accommodation of electrical wires 56 which are inserted between layers 52 and 54 and which extend along the longitudinal axis of the cavities 54.

It, of course, will be recognized that the two layers 52 and 50 can be made as a single cavity containing layer with the electric wire 56 extending therethrough along the longitudinal axis of each cavity and in sealable relationship with the layer.

Adjacent the upper layer 52 is a copper plate 58 which forms the valving to join the various cavities 54 in series, FIG. 8. Plate 58 merely has a series of slots 60 which join the adjacent cavities 54 of the template layer, superimposed as dotted lines in FIG. 8. For ease of manufacture, the slots 60 extend clear through the thickness of copper plate 58 and, therefore, a second copper plate 62 is placed adjacent thereto to restrict and define the path of sample travel to within the cavities 54 and the crossovers 60. Copper plate 58 also forms a common pole with plate 48 to establish the voltage gradient in the cavities in conjunction with the electrical wires 56. Adjacent copper plate 62 is another insulating layer 64 to electrically isolate the copper plate 62 from the top plate 42.

These various layers are joined and held thereto by connecting means such as a plurality of torque-bolts, not shown, extending through all the layers. The layers must be maintained in gas tight sealable relationship.

Inlet 66 for introducing the sample and the carrier extends through the copper plate 48 and is directed to the start of the series of cavities 54. Outlet 68 exits from the end of the cavity series as per the earlier similar embodiments, FIG. 8. Standard fittings can be employed to connect the inlet and outlet to the balance of the chromatographic equipment.

The composite block 30 can also be arranged in stacked relationship with other similar blocks by merely removing the top aluminum block 42 and connecting outlet 68 with the inlet 66 of a similar composite block. In this manner a plurality of composite blocks can be arranged in stacked relationship to maximize the linear path of travel within a small confined area.

The operation of the various embodiments is quite simple. The chromatographic columns of the subject invention are merely inserted in line with the standard chromatographic equipment and the sample passed therethrough in standard fashion. The use of the geometrically curved shape and/or the electrically isolated central wire to establish the voltage gradient will effect the affinity relationship between the sorbent and the sample to affect accurate and rapid separation for determination of the various components of the sample.

Claims

I claim:

1. A chromatographic column including a central cavity extending therethrough to accommodate a sorbent and excitiation means within the column for cooperating with the sorbent to alter the sorbing characteristics of the sorbent with respect to a sample passing therethrough, said excitation means comprising a thin elongated electrical conducting means extending longitudinally through and along the longitudinal axis of the central cavity and electrically isolated from the column, said electrical conducting means adapted to connect to a potential source to establish a voltage gradient within the cavity between the column and the conducting means.

2. A chromatographic column including a central cavity extending therethrough to accommodate a sorbent and excitation means within the column for cooperating with the sorbent to alter the sorbing characteristics of the sorbent with respect to a sample passing therethrough said excitation means comprising a geometric surface defining the cavity, said surface being curved, symmetrical about the cavities' longitudinal axis and increasing in cross section both from the inlet means and outlet means inward to a point intermediate said inlet and outlet means.

3. A chromatographic column including at least one sorbent accommodating central cavity extending from inlet means to outlet means, said cavity defined by a curved surface symmetrical about the cavities' longitudinal axis and increasing in cross section both from the inlet means and outlet means inward to a point intermediate said inlet and outlet means.

4. The chromatographic column of claim 3, the central cavity being symmetrical about all axes and thusly increasing in cross section from the inlet and outlet means inward to a point equidistant from the inlet means and the outlet means.

5. The chromatographic column of claim 4, the central cavity being defined by the general equation Y = e.sup.-.sup.kx .

6. The chromatographic column of claim 4 wherein a series of said central cavities are coaxially aligned and connected in series so that the outlet means of one central cavity cooperates with the inlet means of an adjacent central cavity.

7. The chromatographic column of claim 3 having a conducting metal block which houses the central cavity.

8. The chromatographic column of claim 7 wherein the conducting metal block consists of two separate sections, each recessed to define one-half of said cavity, said sections connected to form the chromatographic column.

9. The chromatographic column of claim 7, including thin elongated electrical conducting means extending along the longitudinal axis of the cavity and electrically isolated from the metal block, said conducting means adapted to connect to a potential source to create a voltage gradient within the cavity between the electrical conducting means and the conducting block.

10. In a metallic electrical conducting chromatographic column having a passageway extending therethrough, the improvement comprising a thin elongated electrical conducting means extending along the longitudinal axis of the passageway and electrically isolated from the column, said conducting means adapted to connect to a potential source to create a voltage gradient within the cavity between the electrical conducting means and the column.

11. The chromatographic column of claim 9 wherein the elongated electrical conducting means comprises a copper wire.

12. The chromatographic column of claim 9 wherein the elongated electrical conducting means comprises a thin carbon rod.

13. The chromatographic column of claim 7 wherein the metal block is aluminum.

14. A chromatographic column comprised of at least one composite block, said block including at least two layers joined in assembled relationship, said layers internally recessed to define a plurality of separate and spaced elongated cavities joined in series and having an inlet means and an outlet means through the block and in communication with the cavities.

15. The chromatographic column of claim 14 wherein said cavities are defined by a curved geometric surface symmetrical about each cavities' longitudinal axis and increasing in cross section from each end of each cavity inward to a point intermediate said ends.

16. The chromatographic column of claim 15 wherein each cavity is defined by the general equation Y = e.sup.-.sup.kx .

17. The chromatographic column of claim 14 comprising a plurality of said composite blocks, said blocks being joined in stacked relationship so that an outlet means of a first block cooperates with the inlet means of an adjacent block in the stack.

18. The chromatographic column of claim 14 including a nonconducting, heat resistant layer intermediate the two layers, said nonconducting, heat resistant layer including the series of separate and spaced elongated cavities extending clear through the thickness of said layer and at least one of said two layers defining recessed connecting means to join the cavities in continuous series.

19. A chromatographic column comprised of at least one composite block, said block including a plurality of layers joined in assembled relationship, said plurality of layers including a heat resistant top and bottom layer, a nonconducting layer adjacent each heat resistant layer, a conducting metal layer adjacent each non-conducting layer, a central template nonconducting layer means defining a series of separate and spaced elongated cavities extending throughout the thickness of said layer means, at least one of said conducting metal layers defining recessed connecting means to join the cavities in continuous series, an inlet and an outlet means cooperating with said connecting means and said cavities and an elongated conducting wire extending along the longitudinal axis of the cavities and through the layer means, said conducting metal layer adapted to connect to a potential source to create a voltage gradient within each cavity between the conducting wire and the conducting metal layers.

20. The chromatographic column of claim 19 wherein at least certain of said cavities are defined by a curved geometric surface symmetrical about each cavities' longitudinal axis and increasing in cross section from each end of each cavity inward to a point intermediate said ends.

21. The chromatographic column of claim 20 wherein each cavity is defined by the general equation Y = e.sup.-.sup.kx .

22. The chromatographic column of claim 19 wherein the central template layer means comprises two sheets in stacked relationship, said wire extending between the two sheets.

23. The chromatographic column of claim 19 comprising a plurality of said composite blocks, said blocks being joined in stacked relationship so that an outlet means of a first block cooperates with the inlet means of an adjacent block in the stack.