Chemistry: analytical and immunological testing – Including chromatography
Patent
1995-11-21
1998-08-18
Snay, Jeffrey
Chemistry: analytical and immunological testing
Including chromatography
436180, 422 70, 422 82, 422110, 137 13, G01N 3030, F17D 118
Patent
active
057957886
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an improved means for managing liquid flow in small bore tubes or channels. More particularly it relates to apparatus for managing liquid flow in microanalytical and micro-preparative procedures such as capillary electrophoresis and high performance liquid chromatography and electrochromatography.
The techniques of micro high performance liquid chromatography, electrochromatography and/or capillary electrophoresis involve the flow of a liquid phase through capillary tubing which typically has an internal diameter within the range of 2 .mu.m to about 1000 .mu.m e.g. 50 .mu.m. In many of the applications of these micro- analytical and micro preparative techniques it is necessary to provide means for stopping the flow of one liquid phase in the column or tubing and introducing another liquid phase at a selected point in the capillary tubing and/or alternatively providing means for diversion of the liquid phase flow by means of additional inlets and outlets as and when required. To date such management of the flow of liquid phase through the column or tubing is achieved by means of specifically engineered switching valves with capillary tubes connected by means of sleeve connectors or unions into which the capillary tubes are located. These valves which have to be custom built to exacting specifications are very expensive and there are several operational disadvantages associated with their use. Thus the mechanical valves must by chemically inert so that the mobile phase remains uncontaminated by residues from the valve and this requirement limits the choice of the material and lubricants for the valves construction and maintenance. The feting of the valves to the column and the construction of the additional inlets and outlets in the capillary tubing must be achieved with ideally zero dead volume couplings and unions. Further the flow through the valve should not be turbulent so that the analyte peak of interest remains narrow in order to achieve the required degree of resolution.
The problem that arises with use of sleeve connectors or unions is the generation of dead volume between the ends of each capillary. The size of the dead volume may be reduced by the careful positioning of the capillaries and ensuring clean cut ends but it is not possible to reduce the dead volume to zero or to be sufficiently small so as to be insignificant on the scale of operation of an analytical technique such as multi-dimensional electrophoresis. Thus for example simple solid geometry calculations show in a conventional Y piece sleeve connector for capillary tubing of 50 .mu.m internal diameter and 375 .mu.m outer diameter the minimum dead volume will be at least 23 nL and in practice it will be significantly larger. This dead volume is too large for micro-analytical techniques such as capillary electrophoresis which use injection volumes in the order of 5 nL. In these circumstances the resolution of closely spaced peaks can be compromised by convective and eddy current induced mixing which will take place in the dead volume region.
We have now found that the disadvantageous problems associated with the use of mechanical switching valves in capillary tube liquid flow systems can be avoided by the use of rapid freeze and rapid thaw of the liquid phase at appropriate segments of the capillary system. The flow of the liquid phase through the capillary tubing can be stopped if a small segment of the column is rapidly cooled so as to freeze the liquid phase in that segment. Further the thermal capacity of the small segment of the column to be frozen is very small and this allows for rapid freezing and rapid thawing as required.
The disadvantages associated with the sleeve connectors and unions can be overcome by use of micro-channel pathways to connect the various capillary tubes and the present invention provides a means for achieving this.
The present invention therefore provides a means for managing liquid flow through small bore tubing or channels which comprises a means for freezing the liquid
REFERENCES:
patent: 3663203 (1972-05-01), Davis et al.
patent: 4203472 (1980-05-01), Dulaney
patent: 4258740 (1981-03-01), Kaartinen et al.
patent: 4269212 (1981-05-01), Kaartinen
patent: 4766922 (1988-08-01), Kaartinen et al.
Bevan Christopher David
Mutton Ian Martin
Glaxo Group Limited
Snay Jeffrey
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