Liquid purification or separation – With means to add treating material – Chromatography
Reexamination Certificate
2000-03-30
2003-09-30
Therkorn, Ernest G. (Department: 1723)
Liquid purification or separation
With means to add treating material
Chromatography
C210S101000, C210S659000, C422S070000
Reexamination Certificate
active
06627075
ABSTRACT:
FIELD OF INVENTION
The present invention concerns a device for and process of preparing volume flows of liquids in at least one passage of a chromatographic column, for analytical liquid measuring techniques.
BACKGROUND ART
Devices for preparing volume flows of liquids in capillary tubes are used in liquid chromatography, in particular high pressure liquid chromatography (HPLC). Depending on the internal diameters of the separation columns used, HPLC technology is divided into “normal bore technology” for separation columns with internal diameters in the range from approximately 3 to 5 mm, “micro bore technology” for separation columns with internal diameters in the range from approximately 1 to 2 mm, “capillary tube LC technology” for separation columns with internal diameters in the range from approximately 180 to 320 &mgr;m, and “nano LC technology” for separation columns with internal diameters of less than or equal to 100 &mgr;m.
For these applications, pump systems are required to generate or transport liquids at extremely small flow rates or volume flows. These liquids must be transported with high reliability and precision under the effective high pressures in the range of approximately 400 bar.
Two different methods are known at present for transporting and preparing liquids having such small flow rates in capillary tube separation columns for liquid chromatography.
A first method is based on the use of injection pumps. Injection pumps are special single-piston pumps. In contrast to conventional piston pumps, in injection pumps the pistons do not move to and fro during analysis but a single piston stroke takes place. Thus the liquid in an injection pump is always in transport mode. The pump chamber must therefore be dimensioned sufficiently large that a single transport stroke is sufficient for complete separation analysis. The pump chamber is pressurized before analysis as the piston in the pump chamber is pressed forward. During separation analysis no more suction is performed. With this process, a volume flow is possible which is independent of the elasticities within the pump chamber. The elasticities in particular of the seals, drive mechanics and elasticity due to the compressibility of the solvent can be compensated accordingly. A further advantage of injection pump technology is the high precision and reproducibility of the achievable volume flows. As the pump chamber is constantly under pressure during the transport phase, the volume flow essentially depends only on the resolution of the drive and the seal of the total system.
Injection pump technology however only has a low flexibility with regard to the achievement of different analysis times and the use of different column diameters. Both the possible analysis time and the selection of separation column diameter are dependent and limited by the maximum stroke volume of the injection pump available at the time the analysis is to be performed. Furthermore with an injection pump only one high pressure gradient at a time can be achieved. This means that each solvent involved in the analysis requires its own high pressure injection pump.
A further possibility for generating and preparing liquid volume flows in capillary tubes, in particular in chromatographic separation columns, for analytical liquid separating technology is the use of conventional piston pumps suitable for “normal bore technology” in connection with the so-called splitter technology. Here suitable flow splitters are used in order to divide the total flow generated and transported by the pumps into at least two part flows, an excess flow in an excess path and a working flow in a working path. The working flow required in the separation column is adjusted and provided by means of restrictors, i.e., by hydraulic resistances arranged in the excess path. The flow splitters and in particular the hydraulic resistances are usually constructed from “fused silica capillary tubes” with small internal diameters. The length and internal diameter of these elements determine the flow resistance. The total flow rate is divided according to the resistance ratios, where normally the smaller part flows through the separation column.
One advantage of this technology is the low production cost because the splitters and the hydraulic resistances can be produced by the users. The extremely small volumes inside the flow splitters or hydraulic resistances are advantageous here.
One particular disadvantage of the conventional splitter technology however is that the user receives no information on the amount of volume flow passing through the separation column during separation analysis. Therefore the volume flow must be measured in a complex manner with mini-injections using stop watches in order to be able to operate the separation columns efficiently. Furthermore even the smallest changes in flow resistance caused, for example, by a contaminated separation column frit, lead to a considerable change in the column flow, with the result of a correspondingly large retention time shift. In order to alleviate this effect, a hydraulic pre-resistance is sometimes inserted in the working path before the separation column. Thus with approximately the same pressure reductions in the separation column and the pre-resistance, the influence of a blocked separation column frit on the column flow is approximately halved. The use of such pre-resistances however means that only half the pump pressure is available for separation analysis in the separation column.
An object of the invention is to provide a new and improved device for and a process of providing volume flows of liquids in capillary tubes for analytical liquid metrology to achieve an essentially constant working flow volume of the liquid being analyzed independent of back-pressure conditions.
SUMMARY OF THE INVENTION
This task is solved by the features of the claims, in particular in that the device has at least one working sensor and one control device to regulate the working flow rate and/or pressure in the liquid working path, where the control device is coupled to the working sensor and a means for changing the working flow rate. As a result, the working flow, i.e., the volume of liquid flowing through the capillary tube, can be kept essentially constant as a function of the pressure and/or volume conditions in the working path which change for example as a result of disturbance variables.
Suitably the means for changing the working flow volume is formed with a hydraulic resistance, in particular a nozzle. This allows smooth reproducible volume flows.
It is of particular advantage for the hydraulic resistance to have a flow resistance, in particular, to be continuously variable. Thus advantageously, variable hydraulic resistance values or “restrictions” can be set with a single hydraulic resistance. Depending on the pressure and/or volume flow conditions changing in the working path, by corresponding change of the flow resistance, the working flow volume and/or working pressure can be held constant. One particular advantage in using variable hydraulic resistances is that both a volume flow and a pressure control are possible in the working path. With pressure control, the pressure in the working path can be held constant irrespective of the solvent used. Constant pressure in the working path is always advantageous if the solvent in the working path must be changed quickly without allowing the working pressure to become too high. With maximum flow rates, constant pressure in the working path allows a considerable extension of the life of the delicate parts contained in the working path, for example the separation column.
A further advantage in using variable hydraulic resistances is that when correspondingly dimensioned, a very great range of achievable flow rates is possible. If an extremely small flow resistance is used, i.e., with high flow rates through the hydraulic resistance, it is possible to flush the entire device including a degasification unit with high flow rates normally used in “normal bore technology”.
Lorinser Andreas
Weissgerber Hans-Georg
Zimmermann Hans-Peter
Agilent Technologie,s Inc.
Therkorn Ernest G.
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