Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing liquid or solid sample
Reexamination Certificate
2000-04-13
2001-09-18
Ludlow, Jan (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing liquid or solid sample
C073S061550, C073S061560, C204S600000, C204S647000, C210S198200, C422S105000
Reexamination Certificate
active
06290909
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
BACKGROUND OF THE INVENTION
This invention is directed to an apparatus for high pressure injection of a sample into chromatography apparatus generally and into high pressure liquid chromatographic (HPLC) apparatus in particular. The design of this apparatus is such that the phenomenon of sample “tailing” is substantially eliminated. Thus, the apparatus is particularly useful for capillary-based chromatographic systems.
A typical prior art method of injecting a sample into pressure-driven chromatography systems, such as an HPLC apparatus, is illustrated schematically in FIG.
1
. Here, a source of pressure, which in conventional chromatography systems is generally a piston or cam-driven pump, is initially, used to force a stream of buffer solution through a packed HPLC column. At the proper time, a sampling valve is turned admitting a portion of a sample into the flowing buffer solution stream and onto the HPLC column where the various components are separated and pass to a detector for analysis. However, for accurate analysis, particularly for complex samples, it is necessary to control precisely the opening and closing of the sampling valve to minimize flow-induced mixing and dead volume, all of which are very difficult to do.
Miniaturization of the chromatography apparatus offers several advantages including, improved efficiency, greater detection sensitivity, low solvent consumption, speed, and the need for only small quantities of sample (typically in the &mgr;L range). In the extreme, complete microscale chromatography systems have been developed that fit into a single cm-size substrate. Examples of these systems can be found in U.S. Pat. No. 5,885,470 to Parce et al., U.S. Pat. No. 5,858,195 and International Application WO 96/04547 to Ramsey, and U.S. Pat. No. 5,571,410 to Swedberg et al. However, in microanalytical pressure-driven chromatography systems the problem of providing a sample having a well-defined volume is exacerbated. It has been found that it is extremely difficult to define accurately a sample volume injected into the chromatography column since the sample itself is quite small. This is generally a consequence of the fact that sampling valves suitable for pressure-driven microscale chromatography systems are either not available or are incapable of being opened and closed precisely enough to eliminate sample “tailing”, flow-induced mixing and dead volume. Moreover, there can be changes in sample composition since faster migrating compounds will be introduced into the chromatography column preferentially. There have been many attempts to alleviate sample “tailing” problem inherent in pressure-driven microanalytical chromatography systems, none have been entirely successful.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an apparatus that provides a clean injection, i.e., sample injection with substantially no tailing, of a sample into pressure-driven chromatography systems.
It is a further object of this invention to provide an apparatus for injecting a sample into an HPLC system that substantially eliminates sample tailing.
It is yet another object of this invention to provide an apparatus for sample injection into a microanalytical HPLC system.
Another object of the invention is to provide a method for sample injection that yields a well-defined sample volume.
A further object is to provide a method for sample injection into microanalytical chromatography systems.
Sample injection into a chromatography system, and particularly into an HPLC system, is accomplished by the present invention by means of electroosmotic/electrophoretic (EO/EP) injection. Here, a conventional sampling valve, such as that illustrated in
FIG. 1
, is replaced by a pair of injector elements connected in series to a common junction disposed at the inlet to a chromatography column. These elements initiate sample flow through the common junction. At an appropriate time, a pressure pulse from a high pressure pumping system, such as an electrokinetic pump (EKP) drives that portion of the sample residing in the volume of the common junction, and whose size is determined by the volume of the common junction, into the chromatography column. The advantage offered by this means of sample injection is that application of the pressure pulse that drives the sample into the chromatography column eliminates sample leakage from the injector elements thereby providing a well-defined sample plug, i.e., a sample that exhibits substantially no tailing.
REFERENCES:
patent: 5922591 (1999-07-01), Anderson et al.
patent: 6019882 (2000-02-01), Paul et al.
Paul, Phillip H., “Microfluidic Engineering,” Sndia Natl. Lab. [Tech. Rep.] Sand (1998), Sand99-8212, pp. 1-21.*
Christensen et al., Anal. Commun. (1998), vol. 35, No. 10, pp. 341-343.
Arnold Don W.
Neyer David W.
Paul Phillip H.
Ludlow Jan
Nissen Donald A.
Sandia Corporation
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