Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Content or effect of a constituent of a liquid mixture
Reexamination Certificate
2003-05-23
2003-12-23
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Content or effect of a constituent of a liquid mixture
Reexamination Certificate
active
06666074
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to liquid chromatography systems generally, and more particularly to systems for conducting chromatographic analysis at high temperatures. This invention also relates to methods for performing chromatographic analysis on liquid samples at elevated or high temperatures.
BACKGROUND OF THE INVENTION
A number of liquid chromatography systems are in use today, which systems utilize a variety of configurations specifically tailored to particular chromatographic applications. In many of such applications, elevated temperatures have been determined to be helpful in the elution of liquid samples in mobile phases. As a general matter, increased temperature of the liquid mobile phase correspondingly lowers mobile phase viscosity, which allows an increased mobile phase flow rate through the liquid chromatography system while maintaining desired chromatographic analysis attributes. As a result, a number of liquid chromatography systems in use today utilize heating means for elevating the mobile phase temperature as the mobile phase is directed through the system.
Liquid chromatography heating instrumentation and design has typically been confined to the temperature range of ambient to 60° C., and flow rates from zero to three milliliters per minute, as dictated by the particular materials making up the chromatographic systems. A specific limitation to existing chromatographic systems for processing mobile phase streams at elevated temperatures is the packing material utilized in the liquid chromatography columns. Such packing material is typically a silica or less typically a polymer-based material. Silica-based materials are chemically and thermally unstable at temperatures above 100° C., while polymeric materials tend to swell or change shape causing problems in use. Therefore, more temperature-resistant materials must be utilized in order to allow chromatographic analysis of liquid mobile phases above 60° C.
An example of such a thermally-stable material is zirconia which provides relatively stable analytical separations at temperatures even in excess of 200° C. In fact, recent tests have demonstrated that packing materials utilizing zirconia as the substrate material are chemically and thermally stable at temperatures approaching the critical point of water (375° C.).
The significantly raised temperature limits of the mobile phase in liquid chromatography systems made possible by such packing materials provide a number of advantages over typical, relatively low-temperature (<60° C.) chromatography systems. For example, high-temperature mobile phase liquids reflect a correspondingly lower viscosity, such that flow rate through the chromatographic column may be increased while maintaining a substantially laminar flow regime. In addition, advantageous solvent properties may be realized at such elevated or high temperatures. Water, for example, increasingly resembles an organic solvent as temperature increases toward the critical temperature of water. In fact, recent tests and calculations indicate that at 250° C., water exhibits solvent properties approaching those of the pure organic solvents most commonly used in liquid chromatography applications, such as methanol and acetonitrile. Thus, in reversed phase applications, the transfer of the solute from pure water to the stationary phase at high temperature (200° C.) resembles that of the transfer of a solute from a pure organic eluent to the stationary phase at 25° C. The use of only water as a mobile phase is environmentally and economically highly desirable. Further, the decrease in viscosity of water at temperatures above 100° C. may be exploited by substantially increasing mobile phase flow rates, as compared to standard temperature chromatographic systems, thereby substantially decreasing analysis time. Such flow rate increases are made possible by the lower viscosity which correspondingly decreases the back pressure of the mobile phase within the chromatographic column. The decreased back pressure allows increased throughput flow rate without exceeding the mechanical pressure limits of the liquid chromatograph pumping system. A further advantage of high-temperature chromatography is providing the analyst additional means to optimize sample separation and increase resolution of various analytes.
Chromatographic heating systems in use today, however, are generally operated below 60° C., and as such have a number of disadvantages which compromise the overall efficacy of such high-temperature liquid chromatography. Some existing systems utilize conductive or convective heating to the chromatographic column to impart heat energy to the mobile phase for elevated temperature analysis of samples dissolved therein. Such techniques fail to properly “pre-heat” the mobile phase prior to admission into the chromatographic column, whereby mobile phase temperature profiles are created radially and axially within the chromatographic column. Mobile phase temperature profiles are, in general, undesired in liquid chromatography applications, as such temperature profiles typically result in peak broadening.
Some chromatographic heating systems utilize a radiant or convective oven in which some of the chromatographic instruments are placed for elevating the temperature of the mobile phase being transported to the column. Such ovens are typically relatively large in volume to encompass at least a portion of the chromatographic system in a heated environment, and have varied success in elevating respective temperatures uniformly. For example, the desired temperature may not be reached in all locations within the oven, such that the temperature within respective chromatographic instruments may vary depending upon their positions within the oven. In addition, the temperature within the chromatographic column can vary both radially and axially, due to differences in temperature of the incoming mobile phase as compared to that of the oven. A common problem experienced with oven heating systems is the column temperature varying from the desired temperature set point, due either to temperature gradients within the oven or slow thermal equilibration of the column under actual operating conditions.
One method utilized to minimize such temperature gradient conditions is the use of pre-heater devices for elevating the temperature of the mobile phase before directing the mobile phase into the chromatographic column. Such pre-heaters may be in a variety of forms, though most typically a means for imparting a pre-determined amount of heat energy through conductive or convective means is utilized. Because such pre-heaters are typically programmed to provide a pre-defined amount of heat energy to the mobile phase, adjustment for varying environmental conditions and incoming mobile phase temperatures for elevating the mobile phase to a desired temperature set point is not well accomplished by existing systems. Furthermore, such pre-heaters are typically not optimized to deliver the heated mobile phase to the chromatographic column at a temperature consistent with gradient-free adiabatic conditions within the column.
It is therefore a principle object of the present invention to provide a system for performing liquid chromatographic analysis at elevated temperatures, wherein temperature gradients in the chromatographic column are minimized.
It is another object of the present invention to provide a chromatographic system for analyzing samples in mobile phases heated above 100° C.
It is a further object of the present invention to provide a high-temperature chromatographic system which utilizes heated mobile phases in a substantially adiabatic environment through a chromatographic column.
It is a yet further object of the present invention to provide a high-temperature liquid chromatography system in which external energy required to sufficiently heat the mobile phase is minimized.
It is a still further object of the present invention to provide a high-temperature liquid chromatography system having counter-flow hea
Gerner Yuri
Hamberg Kurt P.
Sims Carl W.
Haugen Law Firm PLLP
Politzer Jay L
Systec Inc.
Williams Hezron
LandOfFree
Apparatus for conducting high-temperature liquid... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for conducting high-temperature liquid..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for conducting high-temperature liquid... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3165187