Axial chromatography columns and methods

Abstract

The present invention relates to axial flow chromatography columns and methods for separating one or more analytes in a liquid by the use of such columns. The column comprises a first port for mobile phase and a transverse fluid distribution channel for distributing fluid uniformly throughout the packed bed. The first port comprises an inlet and an outlet having a passageway there between, the outlet having an asymmetric configuration relative to the fluid distribution channel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic transverse sectional view of a chromatography column of the prior art showing the basic features thereof.

FIG. 2 is a three dimensional schematic showing a transverse sectional view of a chromatography column according to the invention.

FIG. 3 is an enlarged schematic transverse sectional view of an end plate of a chromatography column according to the invention detailing the asymmetric configuration of the port relative to the fluid distribution channel.

FIG. 4 is a three-dimensional schematic of a chromatography column according to the invention.

FIG. 5 is a transverse section of the column of FIG. 4.

FIG. 6 is a chromatogram showing the chromatographic separation of acetone on a chromatography column according to the invention, both in upflow (dotted line) and downflow (solid line) mode.

FIG. 7 describes a method for calculating the reduced plate height and asymmetry factor from an eluted peak.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically the general components of a chromatography column 1 as known from the prior art (for example, see U.S. Pat. No. 6,524,484). The column has a cylindrical fluid-impermeable side wall 11, e.g. of stainless steel or a high-strength/reinforced polymeric material which may be translucent. The open top and bottom ends of the side wall 11 are closed by top and bottom end assemblies or units 12, 13. Each end unit has a fluid-impermeable end plate 3 fitting sealingly to plug the opening of the cylindrical wall 11, and preferably made of stainless steel or high-strength engineering plastics material, e. g polypropylene. The end plates are backed up by metal retaining plates 2 bearing against their outer surfaces and projecting radially beyond the side wall as retaining flanges 22 through which tension rods 14 are secured. These link the top and end assemblies 12, 13 and help the construction to withstand high fluid pressures.

Each end plate 3 has a central through-opening 31 for communication between the exterior of the column and the packing bed space 9 defined by the side wall 11 and end assemblies 12, 13. Access through the opening 31 is subdivided into separate conduits, connected externally through a connection manifold 8.

A filter layer 4, typically of filtered or woven plastics or steel, extends across the area of the bed space 9 at the inner surface of the end plate 3. The inner surface 35 of the end plate 3 is recessed behind the filter layer 4, e.g. conically as illustrated, and preferably with the use of support ribs (not indicated) supporting the filter layer 4 from behind, to define between them a distribution channel 34. One of the communication conduits, a mobile phase conduit 33, opens inwardly into this distribution channel 34, as well as outwardly to a mobile phase connector 81 of the manifold 8.

From the manifold 8, an access valve device 5 projects inwardly through the end plate opening 31 and sealingly through a central orifice 41 of the filter layer 4. The access valve 5, governs the communication of one or more conduits from the manifold 8 directly to the bed space 9, i.e. bypassing the filter layer 4. Indicated here are first and second valved conduits 51, 61 governed by the valve 5, and connected externally through connectors 82 of the manifold 8.

In a typical operation of the column, a packed bed of particulate stationary phase material fills the bed space 9 between the top and bottom filter layers 4. The valve devices 5 being closed, a mobile phase is fed in through mobile phase connector 81 (arrow “A”), passes through conduit 33 into the distribution channel 34 and through the filter layer 4 to elute down through the packed bed, effecting separation of its components or analytes. Liquid eluate passes thought the filter layer 4 of the bottom end assembly 13 and out through the mobile phase connector 81 thereof (arrow “B”) for collection as appropriate. While this is an example of“downflow” chromatography, in that chromatographic separation is effected by the downward movement of the mobile phase through the column, the skilled person will understand that separation may alternatively be achieved by “upflow” chromatography, simply by pumping mobile phase upwards through the column and thus reversing the direction of flow. In this mode, mobile phase would enter the column at connector 81 (arrow “B”), move upwards through the stationary phase or particulate medium, and be collected from connector 81 (arrow “A”) at the top of the column.

Columns known from prior art that employ a central access valve as shown in FIG. 1 are typically designed with a conduit (33) as passageway in between the mobile phase connection (81) and the liquid distribution channel (34), where said conduit (33) has the purpose of pre-distributing liquid symmetrically relative to the distribution channel (34). It is therefore designed such that the liquid is fed symmetrically into the distribution channel (34), which may be achieved by designing conduit (33) as an annulus around the central orifice (41) or as an arrangement of multiple bores or channels (for example, see US2002/0125181).

FIG. 1 and the above explanation are to illustrate general relationships of components and a typical mode of operation. The skilled person will understand, and it will also appear from the following description, that other specific constructions and modes of operation may be appropriate for different kinds of processes.

A schematic cross-sectional view of a column in accordance with the invention is shown in FIG. 2. The column 101 comprises a tubular housing 111 which is secured to a first end unit 112 and a second end unit 113 by means of tension rods 114, thus defining a bed space 109. The housing 111 and end units 112, 113 are typically composed of stainless steel or a high-strength plastic material such as polypropylene. In a preferred embodiment, where the column is to be used for the separation of biologically active substances, the material is biologically inert such that it does not elicit an immune response in humans in accordance with United States Pharmacopia (USP) <88> Class VI. Tension rods 114, with heads 116, secure the end units 112, 113 to the side wall 111 to form a fluid-tight bed space 109 which is capable of withstanding high operating pressures.

The column can be packed with particulate medium in the form of a slurry through valve means 120, the valve means 120 comprising a central bore (121) and a longitudinal member 122 having a passageway therein (not shown), and nozzle 124. In FIG. 2 the nozzle 124 is shown in its retracted position but it will be understood that it can be moved to a position within the bed space 109 to facilitate filling of the column (see FIG. 3). A wide range of nozzles can be used which facilitate the distribution and even packing of slurry within the bed space. One alternative for achieving an open/closed functionality at the packing valve and nozzle respectively is to have a nozzle that is fixed in the bed space (and thereby not retractable) and located adjacent to a movable element or sleeve on the inside or outside of the nozzle that opens and/or closes the nozzle depending on its position. Filters 104 are each positioned on the interior face of the end units 112, 113 and act with the side wall 111 to define the bed space 109 and also to prevent leakage of particulate medium from the bed space 109. A distribution channel 106 is located transversely across the face of the first end unit 112 and is in fluid communication with filter 104. The fluid distribution channel acts to facilitate radial distribution of the liquid.

In a simple form, the distribution channel 106 comprises a circumferential groove 106a in the face of the first end unit. The groove is positioned such that it effects the circumferential distribution of liquid emanating from outlet 137 of first port 133 uniformly around nozzle 124.

In another embodiment, the distribution channel also comprises a flat impermeable disc 106c which is sandwiched between a first 106b and second 106d net which are in fluid communication. The nets range in thickness from approximately 0.1 mm to 10 mm, the first net 106b preferably being thicker than the second net 106d. The nets act as spacers and define the height of the distribution channel. Suitable netting includes, for example, SEFAR® Propyltex 05-1000/45 and 05-2400/50 (SEFAR AG, Rushlikon, Switzerland).

In a different embodiment, the distribution channel comprises a ribbed plate which is adjacent to and in fluid communication with a fine net. The ribbing on the plate serves the same function as the netting described previously in defining the height of the distribution channel.

In yet another embodiment, the distribution channel comprises a perforated plate wherein one surface of the plate is dimpled. Once again, the dimpling acts as a spacer in defining the height of the distribution channel.

Thus the different embodiments of the distribution channel all serve to produce a similar three dimensional geometry and thereby achieve the same technical effect.

Mobile phase or liquid containing one or more analytes or substances for separation on the column is added via first port 133 which has an inlet 135, outlet 137 and a passageway 134 therebetween. The configuration of the first port 133 within the end unit 112 is such that it is positioned asymmetrically with respect to the fluid distribution channel 106; in the diagram, both inlet 135, where mobile phase or liquid is taken up into the column, and outlet 137 where it exits onto the distribution channel 106, are shown to have such an asymmetric configuration. However, the skilled person will realise that the essential feature of the present invention is the asymmetric configuration of outlet 137 relative to the fluid distribution channel.

Mobile phase exiting the outlet 137 into the bed space 109 will be distributed evenly across the distribution channel 106, pass through filter 104 and then be eluted uniformly through the bed of particulate medium. The mobile phase will finally exit the column through second port 140. The asymmetric configuration of outlet 137 relative to the distribution channel 106 simplifies the design requirements in producing end unit 112 and thus reduces manufacturing costs.

It will be understood by the skilled person that the column may be operated in either a “downflow” mode, as described above, or in an “upflow” mode where the direction of flow of the mobile phase is reversed such that it moves up the column. In upflow mode, mobile phase will enter the column via second port 140, move upwards through the bed of particulate medium, and exit the column and be collected via first port port 133.

In the diagram shown, second port 140 comprises a passageway 142 which extends vertically through end unit 113 and exits on the opposing, exterior face of the unit. In another embodiment (not shown) the second port 140 exits through a lateral face of unit 113; this configuration allows, by means of appropriate connectors or hollow members (not shown), the collection of mobile phase/liquid at the same elevation as that at which it is applied to the column (i.e. at end unit 112; see for example FIG. 4 or 5). The application and collection of mobile phase at the same elevation on a single end unit simplifies use, in terms of operator access and handling, reduces the risk of air accessing the system and decreases the space necessary to set up the column.

Handles 150 facilitate lifting and manipulation of the column.

It will be understood that a wide range of column capacities is possible, typically ranging from 0.1 to 2000 liters. Preferred capacities when using the column as a disposable column are in the range of 0.5 to 50 liters.

FIG. 3 is an enlarged transverse sectional view of the end plate 212 of a chromatography column according to the invention (as shown in FIG. 2) which shows the inlet 235 and details the asymmetric configuration of the outlet 237 of port 233 relative to the fluid distribution channel 206. The central position of the valve means 231, relative to the fluid distribution channel 206, is shown in FIG. 3. As can be seen, nozzle 224 has been lowered into bed space 209 in order that the bed space 209 can be filled with particulate medium in the form of a slurry. It will be understood that the nozzle 224 will be retracted into the body of the longitudinal member 222 once the column has been packed with the particulate medium and prior to any chromatographic separation on the column. A bed of packed particulate medium is obtained by conventional means well known in the art, for example by the movement of one of the end units to compress the bed.

A liquid which contains one or more analytes to be separated is introduced onto the column via inlet 235 of first port 233, via passageway 234 and outlet 237. In the embodiment shown, the fluid distribution channel 206 comprises a circumferential groove 206a, and a flat impermeable disc 206c which is sandwiched between a first 206b and second 206d net which are in fluid communication. The elements effect a radial distribution of liquid across the surface of the particulate medium (not shown) adjacent to filter 204. The liquid then passes through filter 204 into the bed space 209 that is packed with particulate medium (not shown).

Chromatographic separation of analyte(s) which has been introduced onto the particulate medium in this manner is effected by introduction and elution by mobile phase. The mobile phase is added to the column in the same way as described for the liquid above (i.e. via inlet 235 of port 233 and thence, from outlet 237 through distribution channel 206 and filter 204, into the bed space 209). The resulting fractions of mobile phase are collected as described in FIG. 2 above.

As described in relation to FIG. 2 above, it will be understood that the column exemplified in FIG. 3 may also be operated in an upflow mode, with mobile phase entering the column at the second port (not shown), moving upwards through the column and being collected from first port 233.

A three dimensional schematic representation of another embodiment of a chromatographic column 301 in accordance with the present invention is shown in FIG. 4. The external features of the column are clearly seen from the figure. The column comprises a first end unit 312, second end unit 313 and housing 311 which are secured together to form a fluid-tight seal by tension rods 314 and heads 316. Particulate medium in the form of a slurry can be introduced into the bed space (not shown) via valve means 320. First port 333 serves as a conduit for mobile phase or liquid containing analyte(s) to be separated on the particulate medium. Hollow member 360, which is in fluid communication with a second port (not shown) for the mobile phase from the bed space, ends in third port 365 from which appropriate fractions of mobile phase eluted from the column may be collected. As can be seen, third port 365 is at the same level or elevation as the first port 333 through which mobile phase is introduced. This arrangement facilitates user operation and sample handling. In the embodiment shown in FIG. 4, the capacity of the column is approximately 10 liters; it will be understood that a wide range of column capacities are possible, typically ranging from 0.1 to 2000 liters. Preferred capacities when using the column as a disposable column are in the range of 0.5 to 50 liters.

FIG. 5 shows a transverse sectional view of the column of FIG. 4. The column 401 comprises a tubular housing 411, a first end unit 412 (partially shown) and second end unit 413, secured together to form a fluid tight seal by means of tension rods 414. Valve means 420 and first port 433 are shown in the figure. The second port 440 comprises a passageway 442 which extends through second end unit 413 to, and is in fluid communication with (via hollow member 460), a third port 465 from which liquid can be added or collected. As is evident from the figure, the third port 465 is at essentially the same level or elevation as the first port 433, thus facilitating the addition and collection of mobile phase to/from the column. This arrangement has further advantages in that it assists in the installation of the column, decreases the risk of syphoning, and reduces the likelihood of introduction of air into the column.

FIG. 6 shows the chromatographic separation efficiency by example of a tracer pulse experiment achieved on a 10 liter column in accordance with the invention, operated in both downflow (solid line) and upflow (dotted line) mode. The column was packed with a bed of CAPTO™ Q anion exchange resin (GE Healthcare, Uppsala, Sweden) of 85 μm agarose particle diameter. The column had a volume of 10.81, a diameter of 263 mm and a bed height of 200 mm. Acetone (1% of packed bed volume) was used as a tracer substance and eluted from the column using water as mobile phase and the absorbance monitored at 280 nm. As can be seen from Table 1 below, excellent column efficiency was observed with the 85 μm agarose medium used, either in downflow (solid line) or upflow (dotted line) mode.

	TABLE 1
	Observed	Acceptance
	Plates/meter	4430	>3700 (for 85 μm)
	(N/m)
	Reduced plate height	2.5	<3.0
	(h)
	Peak asymmetry	1.14	0.8-1.8
	(Af)

The data from Table 1 were derived from the chromatogram of FIG. 6 as described below.

As a measure for column efficiency, the reduced plate height is determined with help of the peak width w_h at half the height of the eluted peak, as shown in FIG. 7. This procedure is an approximation valid for the gaussian-shaped. In practice, eluted peaks often deviate from this ideal gaussian shape and peak skewness is described qualitatively by a so-called asymmetry factor A_f, where ‘leading’ in the RTD is indicated by A_f<1 and ‘tailing’ by A_f>1. Commonly applied acceptance criteria for the asymmetry factor are 0.8<A_f<1.5-1.8, depending on the type of application.

$h=\frac{\mathrm{HETP}}{d_P}=\frac{L}{d_p}\frac{1}{5.54}{\left(\frac{w_h}{V_R}\right)}^2$ A _f =b/a   (see FIG. 7)

As a rule of thumb, the characteristic dispersion of the medium typically gives a reduced plate height in the range h=1.5-2.0 at an optimized superficial velocity when considering the highly porous media used for protein chromatography in biotechnological downstream processing. The ideal efficiency of the medium has to be compared to the experimentally determined efficiency of the chromatographic system, where an increase in the reduced plate height is a result of additional dispersion from peripherals, sample volume, bed heterogeneities and distribution system. In practice, a typical standard installation qualification of a chromatographic unit used in ion exchange separations of proteins is an experimentally determined reduced plate height of h_{Unit,Apparent}<3.0.

Af   asymmetry factor
dp   particle diameter
h    reduced plate height
HETP height equivalent of a theoretical plate
L    bed height, packed bed
us   superficial velocity in packed bed
VR   retention volume
wh   peak width at 50% of max. peak height

It is apparent that many modifications and variations of the invention as hereinabove set forth may be made without departing from the spirit and scope thereof. The specific embodiments described are given by way of example only, and the invention is limited only by the terms of the appended claims.

Claims

1. An axial flow chromatography column comprising: a housing comprising a side wall;axially spaced first and second end units positioned opposed to each other are separated by said side wall;a transverse fluid distribution channel which is part of or adjacent to said first end unit;a first filter which is adjacent to said transverse fluid distribution channel and a second filter which is adjacent to the second end unit wherein said first and second filters together with the side wall define an enclosed bed space for containing a bed of particulate medium therein;the first end unit including a valve means having a central bore which is in fluid communication with said enclosed bed space, the valve means including a longitudinal member extending through said first filter and said first transverse fluid distribution channel and having a passageway therein, the valve being operably openable and closable to allow filling of the bed space with the particulate medium through said passageway; and a first port for adding liquid to or removing liquid from the bed space;said second end unit includes a second port which is in fluid communication with the enclosed bed space to allow emptying or filling of the bed space with a liquid;

2. The chromatography column of claim 1, wherein said first transverse fluid distribution channel includes a circumferential groove.

3. The chromatography column of claim 1, wherein the first transverse fluid distribution channel additionally includes a planar disc.

4. The chromatography column of claim 1, wherein the first transverse fluid distribution channel additionally includes a net.

5. The chromatography column of claim 1, wherein said first transverse fluid distribution channel includes a ribbed plate.

6. The chromatography column of claim 1, wherein the first transverse fluid distribution channel comprises a perforated plate wherein one surface of said plate is dimpled.

7. The chromatography column of claim 1, wherein said second unit includes a second transverse fluid distribution channel.

8. The chromatography column of claim 7, wherein said second transverse fluid distribution channel of the second end unit is a fluid distribution channel.

9. The chromatography column of claim 1, wherein said longitudinal member of said valve means includes a nozzle.

10. The chromatography column of claim 9, wherein said nozzle is retractable to a position outwith the bed space.

11. The chromatography column of claim 1, wherein said central outlet does not allow emptying of the bed space of particulate medium.

12. The chromatography column of claim 1, wherein said column is pre-packed with particulate medium.

13. The chromatography column of claim 11, wherein said column is a disposable column.

14. The chromatography column of claim 1, further comprising a hollow member which is in fluid communication with the second port, said hollow member having a third port therein for the collection or addition of liquid.

15. The chromatography column of claim 14, wherein the first port and the third port are at essentially the same level or elevation above the level of the bed space on said chromatography column.

16. A method for separating one or more analytes in a liquid from each other, comprising: applying said liquid containing said one or more analytes to an axial chromatography column of claim 1, said column containing a bed of particulate medium therein;eluting said one or more analytes with a mobile phase; andcollecting fractions of said mobile phase eluting from the column.

17. A method for performing a chemical or biochemical reaction between analytes in a liquid or between one or more analytes in a liquid and a substance attached to a particulate medium, comprising: applying said liquid containing said one or more analytes to an axial chromatography column of claim 1, said column containing a bed of said particulate medium therein.

18. A system for separating one or more analytes in a liquid from each other, said system comprising: an inlet or inlet manifold in fluid communication with said liquid;a pump;a chromatography column of claim 1; andan outlet or outlet manifold.