Measuring and testing – Gas analysis – Gas chromatography
Reexamination Certificate
2002-02-04
2003-03-11
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Gas chromatography
C073S023250, C210S198200, C422S089000
Reexamination Certificate
active
06530260
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to gas chromatography systems for generally continuously sampling chemical samples and detecting desired compounds therefrom. In particular, the subject invention is directed to gas chromatographic (GC) column modules for temperature programmed analysis as well as a gas chromatography oven having a door (or a wall) designed specifically to be removably integrated with the column GC modules external the oven cavity in order that the GC oven may be operated isothermically at an elevated temperature for efficient gas chromatography analysis.
Moreover, the present invention relates to a gas chromatography system which includes capillary gas chromatographic column members, temperature sensing mechanisms and heating mechanisms formed into gas chromatographic column modules which are located at the door of a gas chromatography oven in a manner to optimize thermal effect and produce an overall low power consumption system.
BACKGROUND OF THE INVENTION
In the field of gas chromatography, sample tests are typically administered in a temperature controlled oven. For example, as described in U.S. Pat. Nos. 4,420,679; 5,665,314; and, 5,830,353, a capillary GC column which is usually contoured as an extended tube wound in a generally circular fashion is suspended in the GC oven between a sample injector and a sample detector.
The temperature programming of capillary gas chromatography columns is standardly practiced by electronic control of the temperature of a GC oven containing the gas chromatography column. To achieve rapid and uniform temperature response of the gas chromatography column assembly to temperature changes in the oven, capillary gas chromatography columns are standardly packaged by winding the columns on a wire frame support. The winding of the columns on the wire frame support provide extensive surface contact of the capillary gas chromatography column with the heated air in the oven for rapid temperature calibration of the capillary gas chromatography column with the oven air. In laboratory gas chromatography ovens, the air within the oven is typically mixed with a fan to achieve temperature uniformity within the oven.
When a sample is injected through the injector port, it travels through the column until it reaches the detector port. For the standard practice of temperature programming in gas chromatographic analysis, the temperature in the oven containing the gas chromatography column is gradually increased to extend the range of gas chromatography separation capability. The use of capillary columns have become standard practice in laboratory gas chromatography instrumentation and the wide range of separation capability has been made possible through variation of the chemical compositions of the polymers which coat the inner walls of the capillary gas chromatography column. A number of polymer coatings are commercially available for capillary gas chromatography columns having standard thickness, column length, and column inner diameters to optimize the chemical separation required of the gas chromatography.
The need for rapid temperature programming of miniature chromatographic analysis instrumentation may be accomplished by several design techniques. For example, as described in U.S. Pat. No. 5,014,541, the standard gas chromatography oven is replaced by a tubular heat conductor support on which the gas chromatography column is wound. A heating element within the tubular support is used for temperature programming. In another technique, described in U.S. Pat. No. 3,159,996 a glass tube with three parallel bores and sufficient length to contain a heater wire is provided. A resistance thermometer wire (temperature sensor), with the remaining bore coated on the inside functions as a gas chromatography column. As described in U.S. Pat. No. 5,005,399, a thin film coated capillary gas chromatography column is wound on a mandrill consisting of an insulating material. Electrical current passed through the thin film surrounding the gas chromatography column is used to resistively heat the column.
As described in U.S. Pat. Nos. 5,782,964; 6,209,386; and 6,217,829, gas chromatography systems include a capillary gas chromatography column member is provided which contains a chemical sample to be analyzed, a heating mechanism which extends through the length of the capillary gas chromatography column member, and a temperature sensing mechanism for measuring the temperature of the capillary gas chromatography column member which is mounted adjacent to the column member and are bound together into the gas chromatography system. The gas chromatography systems are placed into a gas chromatography containing the column through which chemical samples are passed and thereby separated.
The ability to readily use these commercially available gas chromatography column technologies in small portable gas chromatography instruments (modules) is desirable for the practical realization of similar analytical capabilities in portable or small gas chromatography instruments.
A number of different technologies have been developed as alternatives to standard air circulation ovens for temperature control in gas chromatography. These technologies have sought to achieve faster GC column heating rates (i.e., fast temperature programming, especially at elevated temperatures), smaller instrument sizes, reduced power consumption, etc. A straightforward approach to working with injectors and detectors in existing GC ovens is to place a heating device directly within the oven to apply local temperature control of the column between its connections to the injector and detector within the GC oven.
Using this approach, resistive heating technology for direct heating of a capillary GC column has been packaged for use in a standard GC oven commercially provided by Thermedics Detection, Inc. (Woburn, Mass.). Thermedics Detection, Inc. has developed a “retrofit” GC system in which a column module is placed within the GC oven, coupled between the detector and injector connection ports, and is remotely controlled by an electronics package separate from the GC instrument. Such a direct approach allows the Thermedics Detection, Inc. system to utilize the fast column heating technology in conjunction with existing sample preparation/injection technique, as well as detection hardware without any changes thereto. Further, data acquisition, analysis and management software that commercially exists may be used in such a system.
In an alternative approach, designed by MT Systems (as described in U.S. Pat. No. 6,093,921), a microwave heated capillary column is placed in a small microwave cavity within the laboratory GC oven to achieve a retrofit GC system for faster temperature programming. This microwave cavity similarly heats most of the columns spanning from the injector to the detector in the oven and is remotely powered by an electronics package separate from the GC instrument.
One of the technical challenges, however, in integrating auxiliary column heating technology into an air circulation GC oven, is the prevention of “cold spots” along the GC column between the injector and detector ports. In the practice of temperature programmed GC, the increased temperature selectively passes compounds having specific boiling points through the column to effectively separate compounds having a wide range of boiling points as known to those skilled in the art. Any “cold spots” in the sample path slow or effectively halt the transit of the sample vapor through the column, thus resulting in delay of the analysis along with degradation or complete loss of detection of the higher boiling point component from a sample injected for analysis.
The injectors and detectors of laboratory GC instruments generally have their own temperature control independent of the oven temperature. The injector/detector's temperatures are typically set close to the maximum analysis temperature required to insure that the samples are vaporized quickly and propagate through the GC column without experien
Everson James F.
Mustacich Robert V.
Richards John P.
Politzer J L
Rosenberg , Klein & Lee
RVM Scientific, Inc.
Williams Hezron
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