BACKGROUND
High performance liquid chromatography (HPLC) is a process by which one or more compounds from a chemical mixture may be separated and identified. Chromatography columns are used for any type of separation where a sample is loaded and eluted from the column in order to obtain separation of one or more components. Examples include analysis columns for identifying constituents, preparation columns for separating constituents prior to analysis and guard columns which protect analysis columns by separating out impurities before they can contaminate the analysis column.
In a particular example of an analysis column, a transport liquid, for example a solvent, is pumped under high pressure through a column of packing medium, and a sample of the chemical mixture to be analyzed is injected into the column. As the sample passes through the column with the liquid, the different compounds, each one having a different affinity for the packing medium, move through the column at different speeds. Those compounds having greater affinity for the packing medium move more slowly through the column than those having less affinity, and this speed differential results in the compounds being separated from one another as they pass through the column.
The transport liquid with the separated compounds exits the column and passes through a detector, which identifies the molecules, for example by spectrophotometric absorbance measurements. A two dimensional plot of the detector measurements against elution time or volume, known as a chromatogram, may be made, and from the chromatogram the compounds may be identified.
The column is not a permanent component of the chromatograph, but is designed to be removed and replaced as necessary, for example, to perform different analyses or substitute a new column for a clogged or contaminated column, or one whose packing material has degraded. Replacing columns on chromatographs is generally a tedious and time consuming process. The columns are typically connected to capillary tubes having ferrules that are compressed against mating surfaces within the column by threaded nuts. Removing and replacing these nuts to change a column typically requires the use of hand tools and is a time consuming and awkward process. It would be advantageous to simplify this process.
SUMMARY OF THE INVENTION
The invention concerns a device for holding an elongated item, such as a chromatograph column. The device comprises a base member. A first mounting bracket is positioned on the base member. A first fitting is positioned on the first mounting bracket. The first fitting is adapted to engage one end of the elongated item. A second mounting bracket is positioned on the base member in spaced relation to the first mounting bracket. The second mounting bracket is movable on the base member toward and away from the first mounting bracket. A second fitting is positioned on the second mounting bracket. The second fitting is adapted to engage an opposite end of the elongated item. A restraining mechanism is positioned between the base member and the second mounting bracket. The second mounting bracket is movable away from the first mounting bracket for positioning the elongated item between the fittings. The second mounting bracket is movable toward the first mounting bracket and permits engagement of the first and second fittings with the ends of the elongated item at a predetermined position of the second mounting bracket. The restraining mechanism is engageable between the base member and the second mounting bracket and holds the second mounting bracket at the predetermined position when engaged.
The invention also concerns a method of holding a chromatography column. The method comprises:
- providing a pair of mounting brackets, at least one of the brackets being movable toward and away from the other bracket, each of the brackets having a fitting engageable with an end of the column;
- moving at least one of the brackets away from the other;
- positioning the column between the brackets;
- moving at least one of the brackets toward the other so as to engage the fittings with the ends of the column.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view of a chromatograph having holding device embodiments according to the invention;
FIGS. 2 and 2A-2C are partial sectional side views taken at line 2-2 of FIG. 1;
FIG. 3, is a cross sectional view taken at line 3-3 of FIG. 1;
FIGS. 4A and 4B are partial sectional side views taken at line 4-4 of FIG. 1; and
FIG. 5 is a partial sectional side view of another embodiment of the invention.
DETAILED DESCRIPTION
FIG. 1 shows a chromatograph 10 having columns 12 and 14 connected to capillary tubes 16. The columns are positioned between heating and cooling fins 18 that maintain the columns at a desired temperature as is typically the setup for analysis of the chemical compounds that flow through the columns with a transport liquid.
FIG. 2 illustrates an embodiment of a holding device 20 according to the invention. Holding device 20 comprises a base member 22 that is attachable to the chromatograph 10. The base may be any type of structure, for example a plate as shown, or a frame, which serves to support the items positioned on it. Two mounting brackets 24 and 26 are positioned on the base member 22 in spaced relation. Fittings 28 and 30 are positioned, respectively, on brackets 24 and 26. The fittings provide connectivity between the capillary tubes 16 and the column 12, and to that end, each fitting has a ferrule 32 that engages a mating receptacle 34 within the column to provide a fluid tight joint.
At least one of the fittings is movable toward and away from the other to allow the column 12 to be removed from or positioned between them when changing columns. This may be accomplished by moving the fitting relatively to its mounting bracket, moving one mounting bracket on the base member 22 relatively to the other mounting bracket, or preferably by moving the fitting relatively to the mounting bracket and the mounting bracket on the base.
In embodiment 20, shown in FIG. 2, fitting 28 comprises a jackscrew 36 that threadably engages the mounting bracket 24, thereby allowing motion of fitting 28 toward and away from fitting 30 upon rotation of the jackscrew. The jackscrew rotates independently of the ferrule 32 and the capillary tube 16, and an elongated nipple 38, positioned between the jackscrew and the ferrule, allows the jackscrew to compress the ferrule against the receptacle 34 recessed within the column 12. To facilitate manual turning of the jackscrew, a knurled knob 40 is attached.
Mounting bracket 24 is preferably movable lengthwise along base member 22 toward and away from the other mounting bracket 26. As best shown in FIG. 3, the motion of the mounting bracket is guided by inwardly projecting feet 42 on the bracket that engage slots 44 positioned on opposite sides of the base member. Motion of the bracket is further controlled by a restraining mechanism 46, best shown in FIG. 2A, and preferably in the form of a ratchet 48 positioned on base member 22, and a pawl 50, positioned on bracket 24. Ratchet 48 has teeth 52 that engage a tooth 54 on the pawl. The ratchet teeth 52 are preferably oriented such that the pawl tooth 54 can slide over them when the mounting bracket 24 is moved toward the other mounting bracket 26, but the pawl tooth engages with the ratchet teeth to prevent motion of the bracket 24 in a direction away from the bracket 26. Disengagement of the pawl tooth 54 from the ratchet teeth 52 is effected by rotating the pawl, and this allows the mounting bracket 24 to be moved away from the other bracket 26. It is advantageous to bias the pawl 50 so that the pawl tooth 54 is positively engaged with the ratchet teeth 52 until the pawl is intentionally rotated to disengage the teeth and allow the bracket to move. Biasing is preferably accomplished by a spring 56 extending between the mounting bracket 24 and the pawl 50.
It is understood that other forms of restraining mechanisms may also be used to control the motion of bracket 24, including for example set screws, detents, clamps and worm or spur gears. It is also understood that the bracket 26 and fitting 30 may be movable similarly to bracket 24 and fitting 28 as shown, or they may be fixed in position relatively to the base member 22.
One mode of operation of the device is described with reference to FIGS. 2A-2C. As shown in FIG. 2A, one or both of the mounting brackets 24 and 26 are moved lengthwise along base member 22 away from one another to provide sufficient space between them to permit column 12 to be positioned between fittings 28 and 30. Motion of the brackets is effected by disengaging pawls 50 from ratchet 48 and sliding the brackets along slots 44. Once the column is positioned between the fittings, as shown in FIG. 2B, one or both of the brackets 24 and 26 are moved toward each other and the fittings 28 and 30 are engaged with the ends of the column so that the ferrules 32 are received within receptacles 34. The brackets slide readily, guided by the feet 42 within slots 44, the motion of the brackets toward one another being permitted by the orientation of the ratchet teeth 52 which allow the pawl tooth 54 on each pawl to slide over them without restraining engagement. With the ferrules 32 engaged with receptacles 34 as shown in FIG. 2C, one or both of the fittings 28 and 30 may be advanced by rotating the jackscrews 36. This may be done manually using knob 40, or, if additional torque is required, with a wrench on a nut 58 which may be used instead of the knob. With the pawl 50 engaged with the ratchet 48, motion of the mounting brackets away from one another is prevented, and the advance of the jackscrew 36 serves to increase the compression on column 12, forcing the ferrules 32 into the receptacles 34 and ensuring a fluid tight seal between the column 12 and the capillary tubes 16. Column 12 may be removed by disengaging the pawl 50 on one of the brackets and sliding the bracket away from the other bracket, thereby immediately releasing the column without the need for tools.
In another embodiment of the device 60, shown in FIGS. 1 and 4A, column 14 is positioned between two mounting brackets 24 and 26, bracket 24 having a toggle mechanism 62 mounted thereon to move the fitting 28. Fitting 28 is slidably mounted on bracket 24. Toggle mechanism 62 comprises a first link 64 pivotally attached to fitting 28, and a second link 66 pivotally attached to bracket 24. The first and second links are also pivotally attached to one another to form the toggle joint. The links 64 and 66 may be pivoted using a lever 68 to withdraw the fitting 28 from the receptacle 34 (FIG. 4A), or to advance the fitting into engagement with the receptacle and lock it into position (FIG. 4B) when the links pass over center into the locked position, the second link 66 contacting a stop pin 70 on the bracket 24 which prevents further motion of the toggle mechanism when locked. Action of the toggle mechanism 60 forces the ferrule 32 into engagement with the receptacle 34, the toggle cooperating with the fitting 30 on the other mounting bracket 26 (see FIG. 1) to compress the column between the fittings and ensure a fluid tight seal between it and the capillary tubes 16. Release of the column 14 is effected as described above, by disengaging the pawl 50 from the ratchet 48 (see FIG. 4B) and moving bracket 24 away from bracket 26.
In another embodiment 72, shown in FIG. 5, motion of the mounting brackets 24 and 26 along base member 22 is effected by a motor 74 that rotates elongated screw shafts 76 and 78 about an axis 79 oriented lengthwise along the screw shafts. The screw shafts are threadedly engaged with the brackets which slide along base member 22 guided by slots 44 in response to rotation of the screw shafts. When they are not rotating, the screw shafts restrain the motion of the mounting brackets along the base member. The motor 74 may be controlled by a control device, such as a multiple throw switch 80 which allows the screw shafts to be stopped, to be rotated in one direction to move the brackets away from one another (shown in dashed line) to permit a column 12 to be positioned between fittings 28 and 30, and then to rotate the screw shafts in an opposite direction to bring the mounting brackets toward one another and engage the fittings 28 and 30 with the column ends. Although the embodiment shows both brackets being movable by motor 74, it is also feasible to move only one of the brackets in this manner, the other mounting bracket being fixed in position on the base or adjustably movable, using a ratchet and pawl assembly or other mechanism as described above. Furthermore, the motor may be coupled to the screw shaft or shafts via a clutch (not shown) to prevent damage to the motor, the screws and the brackets when the brackets are at the end of their travel in either direction. A gear box (not shown) may be used to couple the shafts to the motor to increase the torque applied by the motor to the shafts. Upon engagement of the fittings with the column ends, compression force on the column may be adjusted using the jackscrews 36 as described above.
While particular column embodiments are described and shown herein, they are for illustrative purposes only and not meant to limit the scope of the invention. The embodiments of the device according to the invention may be used with any type of chromatography column which may have any shape and a wide range of sizes and operating parameters. For example, columns useable with holding device embodiments according to the invention may have diameters that range from 0.25 inches to over one inch. The column length may vary between several inches up to 10 or more inches. Operating pressures may be between 50 bar and as high as 1000 bar and flow rates up to 50 ml/min are feasible. The columns may be made of metal, such as stainless steel, have glass linings or be formed of fused quartz as well as other materials.
Patent Application
20070084982
