Patent Description:
In GC systems, the amount of time required for a chemical compound to traverse the entire length of a separation column ("column") is known as its retention time. One factor that contributes to the retention time of a chemical compound is the temperature of the separation column. Controlling the temperature of the column precisely from analysis to analysis is beneficial to provide repeatability in the retention time for a particular chemical compound, or analyte. In addition, programmatically changing the column temperature while the sample analytes are migrating through it can advantageously provide shorter analysis time and reduce peak broadening.

Often, columns are heated in known systems using an air convection oven because of its ability to provide a uniform and repeatable thermal environment in a space large enough to accommodate a wide variety of column diameters and lengths. The columns are typically arranged on a support structure that creates an open cylinder. This allows the heated air access over all the column surfaces and results in uniform temperatures across the entire column length. While air convection ovens are useful, their use comes with clear disadvantages. For example, convection ovens require a significant amount of energy and time to heat up, and a significant amount of time to cool down. This leads, of course, to comparatively long cycle times and high power consumption, among other disadvantages. In addition, the ability to do rapid analysis via temperature programmed conditions is limited when using air convection ovens.

<CIT> discloses a column oven to be used in chromatography and comprising a heat insulation container surrounded by heat insulating material.

What is needed, therefore, is an apparatus that overcomes at least the drawbacks of known GC column heaters discussed above.

The present teachings are best understood from the following detailed description when read with the accompanying drawing figures. The features are not necessarily drawn to scale. Wherever practical, like reference numerals refer to like features.

It is to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. The defined terms are in addition to the technical and scientific meanings of the defined terms as commonly understood and accepted in the technical field of the present teachings.

As used in the specification and appended claims, the terms 'a', 'an' and 'the' include both singular and plural referents, unless the context clearly dictates otherwise. Thus, for example, 'a device' includes one device and plural devices.

As used in the specification and appended claims, and in addition to their ordinary meanings, the terms 'substantial' or 'substantially' mean to within acceptable limits or degree. For example, 'substantially cancelled' means that one skilled in the art would consider the cancellation to be acceptable.

As used in the specification and the appended claims and in addition to its ordinary meaning, the term 'approximately' means to within an acceptable limit or amount to one having ordinary skill in the art. For example, 'approximately the same' means that one of ordinary skill in the art would consider the items being compared to be the same.

In the following detailed description, for purposes of explanation and not limitation, representative embodiments disclosing specific details are set forth in order to provide a thorough understanding of the present teachings. Descriptions of known systems, devices, materials, methods of operation and methods of manufacture may be omitted so as to avoid obscuring the description of the example embodiments. Nonetheless, systems, devices, materials and methods that are within the purview of one of ordinary skill in the art may be used in accordance with the representative embodiments.

Relative terms, such as "above," "below," "top," "bottom," "upper" and "lower" may be used to describe the various elements' relationships to one another, as illustrated in the accompanying drawings. These relative terms are intended to encompass different orientations of the device and/or elements in addition to the orientation depicted in the drawings. For example, if the device were inverted with respect to the view in the drawings, an element described as "above" another element, for example, would now be "below" that element. Similarly, if the device were rotated by <NUM>° with respect to the view in the drawings, an element described "above" or "below" another element would now be "adjacent" to the other element; where "adjacent" means either abutting the other element, or having one or more layers, materials, structures, etc., between the elements. As used herein, an element "disposed over" or "disposed below" another element means the element is "adjacent to" the other element. "Directly adjacent" means abutting the other element.

The invention is defined in the independent claim <NUM>.

<FIG> is a simplified block diagram of a GC system <NUM> in accordance with a representative embodiment. Many aspects of the GC system <NUM> are known to one of ordinary skill in the art. As such, details of certain known components of the GC system <NUM> are omitted. In certain instances representative examples of known components that may be implemented are noted, but are presented for illustration and are, in no way, intended to be limiting.

The GC system <NUM> comprises a sample inlet <NUM>. The sample inlet <NUM> is fluidically coupled to a contaminant trap <NUM>. The contaminant trap <NUM> is fluidically coupled to a column <NUM>, which may be one of a variety of columns useful in gas chromatography. In an embodiment, the contaminant trap <NUM> may be as described in concurrently filed, commonly owned <CIT>). The contaminant trap <NUM> is a microfluidic contaminant trap configured to trap contaminants in the sample from the sample inlet <NUM> and to prevent the trapped contaminants from reaching the column <NUM>. It is noted that the inclusion of contaminant trap <NUM> is merely illustrative, and the present teachings are contemplated for use in GC systems that do not comprise a contaminant trap, or that do not comprise a microfluidic contaminant trap as described in the application referenced immediately above.

The column <NUM> separates the components of a chemical sample. The column <NUM> may be a capillary column comprising a piece of fused silica or metal tubing (not shown) with a coating on the inner portions of the tubing or packed with particles that interact with the sample from sample inlet <NUM> to separate the components of the chemical sample.

The column <NUM> is in thermal contact with a column heating apparatus, which is an aspect of the column temperature control apparatus <NUM>. By virtue of the column temperature control apparatus <NUM>, the retention time is controlled, while the uniformity of the heating of the column <NUM> is improved over previous devices. Furthermore, in certain embodiments, the column temperature control apparatus <NUM> cools the column <NUM> in an efficient manner, ultimately improving repeatability of the retention time of an analyte and analysis cycle time compared to known GC systems. These and other benefits of the column temperature control apparatus <NUM> are described more fully below in connection with representative embodiments.

The column <NUM> is physically and/or fluidly connected to a detector <NUM>, which detects the presence and frequently the quantity of the components separated by the column <NUM>. Generally, the detector <NUM> is a known GC detector such as a flame ionization detector (FID), a mass spectrometer detector (MSD), a thermal conductivity detector (TCD), an electron capture detector (ECD), a nitrogen phosphorus detector (NPD), a sulfur chemiluminescence detector (SCD), a nitrogen chemiluminescence detector (NCD), a pulsed flame photometric detector (PFPD), a helium ionization detector (HID), or a flame photometric detector (FPD).

The GC system <NUM> also comprises a controller <NUM> and a power source <NUM>. The controller <NUM> may be one of a plurality of controllers (not shown) of the GC system <NUM>, or may be the sole controller of the GC system. Presently, the function of the controller <NUM> with respect to maintaining the heating of the column <NUM> by the column temperature control apparatus <NUM> is described. Other functions of the controller <NUM> or of other controllers are not germane to the present teachings and are not described.

Generally, the controller <NUM> can be implemented in numerous ways (e.g., such as with dedicated hardware) to perform various functions discussed herein. A "processor" is one example of a controller, which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform various functions discussed herein. The controller <NUM> may be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions. Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, microcontrollers, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

In various implementations, the controller <NUM> may be associated with one or more storage media (generically referred to herein as "memory," e.g., volatile and non-volatile computer memory such as random-access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), electrically programmable read-only memory (EPROM), electrically erasable and programmable read only memory (EEPROM), universal serial bus (USB) drive, floppy disks, compact disks, optical disks, magnetic tape, etc.). In some implementations, the storage media may be encoded with one or more programs that, when executed on the controller <NUM>, perform at least some of the functions discussed herein. Various storage media may be fixed within the controller <NUM> or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or controller so as to implement various aspects of the present teachings discussed herein. The terms "program" or "computer program" are used herein in a generic sense to refer to any type of computer code (e.g., software or microcode) that can be employed to program the controller <NUM>.

The controller <NUM> is configured to receive temperature data from a temperature sensor (not shown in <FIG>), to interpret the data from the temperature sensor, and to execute algorithms to alter system aspects to achieve the desired column temperature. These functions may be performed by separate controllers, processors or modules. The controller <NUM> is configured to provide control signals to the power source <NUM>. The power source <NUM> is one of a number of known electrical power sources and is configured to adjust the power of the column temperature control apparatus <NUM> to maintain the temperature of the column <NUM> at approximately a desired temperature.

<FIG> shows an exploded view of a column heating apparatus <NUM> (sometimes referred to as "an apparatus") for heating a GC column (not shown in <FIG>) in accordance with a representative embodiment. The column heating apparatus <NUM> comprises a first substrate <NUM>, which is substantially planar. A spacer layer <NUM> is optionally disposed over the first substrate <NUM>. A recess <NUM> is provided in the layer <NUM>, and is configured to receive a temperature sensor <NUM>.

The heater assembly <NUM> is disposed over the first substrate <NUM> and comprises a heating element <NUM> disposed between an optional first intervening layer <NUM> and an optional second intervening layer <NUM>. The first and second intervening layers <NUM>, <NUM> are generally mechanically compliant and made from the same material. Notably, the heater assembly <NUM> is contemplated for use as the heat source in the column temperature control apparatus <NUM> described above in connection with the representative embodiments of <FIG>.

While the heating element <NUM> is shown as a substantially uniform series of traces, it is also contemplated that that the traces may be substantially non-uniform, non-symmetrical, and/or irregular. By way of example, since the outer edge of the heater assembly <NUM> is more exposed to the external environment, a decrease in temperature may occur at the outer edge compared to the inner portions of the assembly. By increasing density and/or changing width of the traces of the heating element <NUM> at its edge, the power density of the heating element <NUM> near the outer edge is increased, and the temperature differential between the inner portion and the outer edge of the heating element, manifest in the noted temperature decrease, may be reduced or eliminated. Further modifications of the thickness of the traces may also have desirable properties as described herein.

First and second intervening layers <NUM>, <NUM> may also be selected to act as electrical insulators between the heating element <NUM> and the first substrate <NUM> and a second substrate <NUM>, which is disposed over the heater assembly <NUM>. Like the first substrate <NUM>, the second substrate is substantially planar. The second substrate <NUM> is configured to have the GC column (not shown in <FIG>) in direct contact therewith or indirect contact therewith (i.e., with an intervening layer (not shown)) between the GC column and the second substrate <NUM>. Illustratively, the GC column is disposed over an upper surface <NUM> of the second substrate <NUM>, and heat from the heater assembly <NUM> is transferred through the second substrate <NUM> to the GC column. As can be appreciated from a review of <FIG>, the upper surface <NUM> is substantially planar.

The first and second substrates <NUM>, <NUM> may comprise a single layer or multiple layers of the same or different materials. As described more fully below, the column heating apparatus <NUM> substantially uniformly heats the GC column contacting the second substrate <NUM>.

In known GC heaters, such as air convection ovens, the oven may require large amounts of power (up to 2000W) to allow temperature programming rates of <NUM>-<NUM>/min. By contrast, as described more fully below, the column heating apparatus <NUM> beneficially provides similar temperature programming rates at substantially less than 100W. In addition, the column heating apparatus <NUM> allows much faster temperature programming rates (e.g., up to five to ten times faster than a known GC heater with <NUM>% of the power requirement of the known GC heater), resulting in faster chromatographic analyses. Also, where known GC heaters may take six or more minutes to cool from <NUM> to <NUM>, the column heating apparatus <NUM> can be operated to take less than three minutes, which allows for faster cycle times between analyses. The column heating apparatus <NUM> realizes these improvements in performance by specifying the material properties of the second substrate <NUM> or the first and second substrates <NUM>, <NUM> to be low thermal mass while maintaining mechanical stiffness, small thermal gradients, and resistance to thermal deformation.

As should be appreciated by one of ordinary skill in the art, the "thermal mass" of an object is a measure of its capacity to store thermal energy (i.e., heat). As such, a material that has a comparatively low thermal mass will require less heat in order to change temperature than one of comparatively high thermal mass. As described more fully below, in order to enable faster heating and cooling, the materials selected for the first and second substrates <NUM>, <NUM> and the heater assembly <NUM> have a low thermal mass.

Thermal mass (with units of J/K) is the product of the specific heat of the material, cp, and the mass of the object, m. For convenience, mass can be further specified as the product of the density, p, of the material, a surface area, As, and a thickness, t, normal to the surface area. Combining, thermal mass can be expressed as: <MAT>.

Since the surface area of the column heating apparatus <NUM> is fixed based on the size of the column to be heated, the surface area is viewed as a constant for this discussion. The remaining terms are examined further. The term, ρcp, is also known as the volumetric heat capacity of the material and is an intrinsic property of the material. To minimize thermal mass, this term should be minimized. According to a representative embodiments, materials for the second substrate <NUM> or the first and second substrates <NUM>, <NUM> have a volumetric heat capacity less than approximately <MAT> at <NUM>.

The selection of material for the second substrate <NUM> or the first and second substrates <NUM>, <NUM> is additionally guided by mechanical stiffness, low thermal gradients, and resistance to thermal deformation. These factors are particularly important in determining the minimum thickness of material required for the second substrate <NUM> or the first and second substrates <NUM>, <NUM>. Along with thermal mass, these are not wholly independent characteristics, so choice of materials is made considering their interrelationship. The ultimate goal is to achieve low thermal gradients across the upper surface <NUM> of second substrate <NUM> while achieving a relatively low thermal mass for first and second substrates <NUM> and <NUM> to enable faster heating and cooling.

Thermal gradients across the second substrate <NUM> or across the first and second substrates <NUM>, <NUM> result from different parts of the substrates being in different thermal environments. The heating element <NUM>, for instance, does not have a completely homogenous thermal profile. In addition, the outer edges of the first and second substrates <NUM>, <NUM> will typically have more exposure to the ambient temperature environment. As such, thermal gradients can exist across the first and second substrates <NUM>, <NUM>. Gradients are reduced when the material chosen for the first and second substrates has low resistance to heat flow, that is, a high thermal conductivity, k. It is desirable, therefore, to have a material with comparatively high thermal conductivity, particularly for the second substrate <NUM>, so that the upper surface <NUM> that touches the GC column is substantially uniform in temperature. According to a representative embodiment, materials for the second substrate <NUM> or the first and second substrates <NUM>, <NUM> have a thermal conductivity greater than approximately <MAT> at <NUM>.

The first and second substrates, <NUM> and <NUM>, provide mechanical structure for the column heating apparatus <NUM>. Notably, the first and second substrates <NUM>, <NUM> support the relatively non-rigid heater assembly <NUM> as well as the layer <NUM> and the temperature sensor <NUM>. Beneficially, materials chosen for the first and second substrates <NUM>, <NUM> are sufficiently stiff to provide adequate support. The stiffness of a material is related to its elastic modulus (or Young's Modulus), E. If a material has a high elastic modulus, then less of it (e.g., a thinner piece of it) is necessary to provide the same stiffness as a material with a lower elastic modulus. It is beneficial, therefore, to have a material with a high elastic modulus so that less (thermal) mass of material is required to achieve adequate stiffness. According to a representative embodiment, materials for the first and second substrates <NUM>, <NUM> have a Young's Modulus greater than approximately <NUM> GPa. In addition to stiffness, the first and second substrates, <NUM> and <NUM> must maintain surface flatness in order to hold the heater and column in direct contact with the upper surface <NUM> , or in indirect contact with the upper surface <NUM> (i.e., with an intervening layer (not shown) between the GC column <NUM> and the upper surface <NUM>). Issues in flatness may occur due to deformation or "buckling" from rapid temperature changes. If large thermal gradients exist in a component such as, for example, when the component is cooled asymmetrically, sections of the component will want to grow due to thermal expansion while other sections will want to remain fixed. In the worst case, this can cause buckling or fracture.

The likelihood of mechanical deformation due to thermal expansion can be minimized by choosing a material with a high thermal conductivity, k, low thermal expansion coefficient, α, or both. A material with high thermal conductivity resists the formation of large thermal gradients within the material. Materials with low thermal expansion do not grow very much even under significant thermal gradients. Choosing materials with a high thermal conductivity, low thermal expansion coefficient, or both, allows for the use of less material (e.g., a thinner piece of it) and therefore less thermal mass while providing adequate resistance to buckling. According to a representative embodiment, materials for the second substrate <NUM> or the first and second substrates <NUM>, <NUM> have a ratio of thermal conductivity to coefficient of thermal expansion greater than approximately <MAT> at <NUM>°C.

Another consideration in the selection of the material for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM> is the electrical insulating properties of the material. Beneficially, the material is substantially electrically insulating to avoid having to add an additional material in the column heating apparatus <NUM> to perform this function.

Finally, it is important to select a material for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM> that is operative in the column heating apparatus <NUM> at temperatures greater than approximately <NUM>.

The table below presents a summary of some of the factors to be considered in selection of the material for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM>.

In a representative embodiment, the second substrate <NUM> comprises silicon. Generally, the silicon layer that forms the second substrate <NUM> has a thickness of approximately <NUM> to <NUM>. Illustratively, the second substrate <NUM> comprises <<NUM>,<NUM>,<NUM>> Si having a thickness of approximately <NUM>. In a representative embodiment, first substrate <NUM> comprises <<NUM>,<NUM>,<NUM>> Si wafer having a thickness of approximately <NUM>, and the second substrate <NUM> comprises two <<NUM>,<NUM>,<NUM>> Si wafers having a thickness of approximately <NUM> each. It was discovered that the use of two wafers for second substrate <NUM> provides somewhat improved retention time repeatability. Notably, the second substrate <NUM> does not require special polishing or doping. Moreover, and although not essential, the first substrate <NUM> may be made of the same material and to the same specifications as the second substrate <NUM>.

It is noted that the use of silicon for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM> is merely illustrative. More generally, the materials selected for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM> are selected to have a volumetric heat capacity (ρcp) less than approximately <MAT> at <NUM>; a thermal conductivity (k) greater than approximately <MAT> at <NUM>; a ratio of thermal conductivity to coefficient of thermal expansion <MAT> greater than approximately <MAT> at <NUM>°C; and a Young's Modulus (E) greater than approximately <NUM> GP.

These physical characteristic are desired in order to achieve faster heating and cooling of the column heating apparatus <NUM> within several bounds including low thermal mass, mechanical stiffness, low thermal gradients and resistance to deformation. Table <NUM> compares these four characteristics across a range of materials.

Based on the foregoing, the material selected for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM> preferentially has a volumetric heat capacity less than approximately <MAT> at <NUM>. Therefore, copper, alumina, nichrome, stainless steel, nickel, sapphire, silicon nitride, tungsten carbide, beryllium oxide, brass, bronze, aluminum brass, iron, and beryllium are not preferred materials for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM>.

The material selected for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM> preferentially has a thermal conductivity greater than approximately <MAT> at <NUM>. Therefore, Pyrex glass, mica, titanium, quartz glass, gallium arsenide, germanium, boron nitride, zirconium oxide, boron carbide, indium phosphide, niobium, rhenium, and tantalum are generally not preferred materials for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM>.

The material selected for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM> additionally preferentially has the ratio of thermal conductivity, k, to the coefficient of thermal expansion, α , that is greater than approximately <MAT> at <NUM>°C (at <NUM>). Therefore, aluminum, magnesium, silver, zinc, and gold are not preferred materials for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM>.

The material selected for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM> additionally preferentially has a Young's Modulus greater than approximately <NUM> GPa. Therefore, graphite is not a preferred material for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM>.

Based on the analysis above, illustrative materials that can be used for the second substrate <NUM>, or the first and second substrates <NUM>, <NUM> and meet all of the preferred material characteristics comprise silicon, aluminum nitride, diamond, silicon carbide, tungsten, molybdenum, alloys of tungsten (particularly with copper), alloys of molybdenum (particularly with copper), and combinations thereof.

Heater assembly <NUM> is disposed over the first substrate <NUM> and comprises a heating element <NUM> disposed between the first intervening layer <NUM> and the second intervening layer <NUM>. The first and second intervening layers <NUM>, <NUM> are generally made from the same material, and each have a second comparatively low thermal mass. Moreover, the first and second intervening layers <NUM>, <NUM> are each made from a material that is electrically insulating. Notably, if the first and second substrates <NUM>, <NUM> are electrically insulating, the first and second intervening layers <NUM>, <NUM> can be foregone. However, if the material can become more electrically conducting at comparatively high temperatures (e.g., silicon), then electrical insulation is needed between the heating element and first and second substrates <NUM>, <NUM>. As such, in a representative embodiment in which first and second substrates are silicon, first and second intervening layers <NUM>, <NUM> are needed. Notably, however, in another representative embodiment, rather than including first and second intervening layers <NUM>, <NUM>, the sides of the first and second substrates <NUM>, <NUM> facing the heating element may be coated with a layer of glass or other dielectric to perform this insulating function.

The heating element <NUM> is illustratively a resistive heating element, such as a wire heater or a foil heater. Other types of heating elements are contemplated. As should be appreciated, the heating element is beneficially quite thin, and thereby does not substantially interfere with the desirably flat nature of each of the layers of the column heating apparatus <NUM>. With known thin film fabrication methods, such comparatively thin heating elements that are within the purview of one of ordinary skill in the art are contemplated.

Like the comparatively low thermal masses of the first and second substrates <NUM>, <NUM>, the comparatively low thermal mass of the first and second intervening layers <NUM>, <NUM> ensures they heat comparatively quickly and will not retain heat very well. As such, the heater assembly <NUM> can be heated quickly across its surface, and will not retain heat to the extent as other materials often used in heaters. Again, the former attribute ensures ultimately that the GC column disposed over upper surface <NUM> of the second substrate <NUM> is heated comparatively very quickly, which improves analysis time. The latter attribute enables the thorough dissipation of heat from the column heating apparatus <NUM> in a relatively quick and efficient manner enabling faster cycle times and improved retention time repeatability.

In a representative embodiment, the first and second intervening layers <NUM>, <NUM> each comprise mica, which are of sheet silicate (phyllosilicate) minerals. Generally, mica materials are
X<NUM>Y<NUM>-<NUM>Z<NUM>O<NUM>(OH,F)<NUM> in which X is K, Na, or Ca or less commonly Ba, Rb, or Cs; Y is Al, Mg, or Fe or less commonly Mn, Cr, Ti, Li, etc.; Z is chiefly Si or Al, but also may include Fe<NUM>+ or Ti. The use of mica for first and second intervening layers <NUM>, <NUM> is merely illustrative, and other materials having similar thermal mass, electrical conductivity, and resistance to mechanical distortion due to rapid temperature change as mica are contemplated. For example, fabrics such as fiberglass, and basalt provide the desired properties.

Generally, the mica layers that form the first and second intervening layers <NUM>, <NUM> of the heater assembly <NUM> each have a thickness of approximately <NUM>. More generally, the material selected for the first and second intervening layers <NUM>, <NUM> of the heater assembly <NUM> has an electrical resistivity of approximately <NUM> × <NUM>^<NUM>Ω·m to approximately <NUM> × <NUM>^14Ω·m, or greater. Since mica has a comparatively low coefficient of thermal expansion (CTE), similar to silicon, it will not expand when heated or cooled and will not suffer from mechanical distortion, Furthermore, the mica is inherently flat and affords intimate contact between the substrate and the heating element. Other materials that could serve as an electrical insulator in place of mica are, for example, aluminum nitride, quartz, glass, silicon carbide, and the fabrics cited above. Compliant materials like the fabrics cited previously need not be as flat as they can be compressed to achieve intimate contact.

Spacer layer <NUM> is optionally disposed over the first substrate <NUM> and beneath the first intervening layer <NUM> of the heater assembly <NUM>. A recess <NUM> is provided in the spacer layer <NUM>, and receives a temperature sensor <NUM>. The spacer layer <NUM> accommodates temperature sensor <NUM>. Illustratively, spacer layer <NUM> is a compliant material, such as a glass fiber material. The spacer layer <NUM> beneficially maintains comparatively even pressure between the first intervening layer <NUM> of the heating element <NUM> and the first substrate <NUM>. Notably, the inclusion of the temperature sensor <NUM> can compromise the even pressure in the absence of spacer layer <NUM>. Uneven pressure between the first intervening layer <NUM> of the heater assembly <NUM> and the first substrate <NUM> can result in a reduction in the overall "flatness" of the column heating apparatus <NUM>, leading to thermal gradients and "hot spots," and can thus compromise performance of the GC column.

As alluded to above, the controller <NUM> receives temperature data from the temperature sensor <NUM>, and based on these data provides control signals to the power source <NUM>. Based on the control signals from the controller <NUM>, the power source <NUM> adjusts electrical power to the heater assembly <NUM> to maintain the temperature of the GC column at a substantially constant value or to cause it to change according to some desired and repeatable program.

<FIG> shows the column heating apparatus <NUM> of <FIG> for heating a GC column after assembly. The column heating apparatus <NUM> includes a grommet <NUM> that is used to secure the various layers of the column heating apparatus <NUM>. Illustratively, the grommet <NUM> comprises stainless steel. Other means of securing the layers are also contemplated, such as brackets, clips etc. The requirements of the grommet or other securing means are that it can tolerate the elevated temperatures (e.g. <NUM>) and still maintain sufficient pressure on the column heating apparatus <NUM>. High temperature metals are the preferred material.

<FIG> shows the column heating apparatus <NUM> of <FIG> having the GC column <NUM> disposed thereover. As shown, the GC column <NUM> is oriented in a comparatively flat spiral and is disposed over upper surface <NUM> of the column heating apparatus <NUM>, and is in thermal contact with the upper surface <NUM>. The GC column <NUM> is in thermal contact with the column heating apparatus <NUM> through either direct contact with the upper surface <NUM> or with a substantially close proximity to the upper surface <NUM> to transfer heat from the column heating apparatus to the GC column. In a representative embodiment, the GC column comprises a fused silica capillary column. The dimensions of the GC column <NUM> vary, but typical inside diameters range from approximately <NUM> to approximately <NUM>. Typical lengths range from approximately <NUM> meters to approximately <NUM> meters. The coiling of GC column <NUM> in representative embodiments may be a substantially planar spiral having one or more "stacked" so that the GC column <NUM> is in thermal contact with the column heating apparatus <NUM>, which is substantially planar, as described above. Notably, GC column <NUM> can be coiled on supports having a diameter of approximately <NUM> to approximately <NUM> in a multi-layer toroid. In some embodiments, more than one GC column <NUM> may be disposed over the column heating apparatus <NUM>, wherein both GC columns <NUM> are in thermal contact with the column heating apparatus <NUM>.

Illustratively, GC column <NUM> has a length up to approximately <NUM> with an inner diameter of <NUM> (or smaller internal diameter) and comprises a fused silica capillary column. Alternatively, GC column <NUM> can have a length less than <NUM> but can have an inner diameter of <NUM>. The column may also be metal and may also be packed with stationary phase.

In operation, after the GC column <NUM> is provided over the upper surface <NUM> of the second substrate, the heating element is activated, and begins to heat the various layers of the column heating apparatus <NUM>. Most importantly, the heater assembly <NUM> heats the second substrate <NUM>, and in turn heats the GC column <NUM>. The heating of the GC column <NUM> is substantially uniform and efficient due to the various characteristics of the components of the apparatus as discussed above. After a specific run is completed, the GC column <NUM> and the column heating apparatus <NUM> are cooled to reach substantially its initial temperature for the analysis. Because of the various components of the column heating apparatus <NUM> as discussed above, the column heating apparatus <NUM> cools comparatively quickly to its initial temperature, and does not substantially retain heat from the previous run. As such, when the next analysis is started, the column heating apparatus <NUM> and the GC column <NUM> are at substantially the same initial temperature from the previous run. Moreover, the cycle time is comparatively improved over other known heating arrangements used in GC systems.

<FIG> shows the column heating apparatus <NUM> of <FIG> having the GC column <NUM> disposed thereover in accordance with another representative embodiment. As can be appreciated, the column heating apparatus <NUM> of <FIG> shares certain aspects, details and features common to those of column heating apparatus <NUM> described in connection with <FIG> above. Often, such common aspects, features and details are not repeated. As noted above, the GC column <NUM> is oriented in a comparatively flat spiral and is disposed over upper surface <NUM> of the column heating apparatus <NUM>, and makes thermal contact with the upper surface <NUM> through the portion that is in direct or close physical contact with the upper surface <NUM>. Again, the coiling of GC column <NUM> in representative embodiments may be a substantially planar spiral having one or more "stacked" so that the GC column <NUM> is in thermal contact with the column heating assembly <NUM>, which is substantially planar, as described above. Persons skilled in the art would appreciate how a GC column <NUM> may be "stacked" or "wound" to achieve the desired objectives described herein. In accordance with the depicted representative embodiment, the GC column <NUM> is held in place over the upper surface <NUM> by GC column supports <NUM> mounted to GC column bracket <NUM>. Illustratively, the GC column supports <NUM> can be constructed of thin strips of metal such as aluminum, nickel, or stainless steel. More generally, the GC column supports <NUM> may be made of a material that is able to support the GC column <NUM> on the upper surface <NUM> and tolerate the temperature exposure (up to <NUM>). The GC column bracket <NUM> serves as a structural element for GC column <NUM> and ensures repeatable positioning of the GC column <NUM> on upper surface <NUM> for reproducible chromatographic performance. The GC column bracket <NUM> can be mounted in the GC system using one or more of a variety of known elements including, but not limited to, screws, clamps, and magnets (not shown).

<FIG> shows an exploded view of a GC column heating apparatus <NUM> (sometimes referred to as "an apparatus") in accordance with a representative embodiment. Many aspects of the column heating apparatus <NUM> are substantially identical to those of column heating apparatus <NUM> described above. As such, many details of various features that are common to those of column heating apparatus <NUM> are not repeated. Notably, the various characteristics of the common elements of the column heating apparatuses <NUM>, <NUM> are the same. In embodiments where the spacer layer <NUM> is omitted, the temperature sensor may be disposed within a substrate <NUM>, <NUM>. In embodiments where the intervening layers <NUM>, <NUM> are omitted, the temperature sensor may be disposed within a substrate layer <NUM>, <NUM> or within the spacer layer <NUM>, which may be located below the first substrate <NUM> (i.e., further away from the heating element <NUM> than the first substrate <NUM>).

The column heating apparatus <NUM> comprises the first substrate <NUM> having heating element <NUM> disposed thereover.

A heater assembly <NUM> comprises heating element <NUM>. Notably, therefore, the heater assembly <NUM> does not comprise first and second intervening layers <NUM>, <NUM>, which were noted above as being optional. However, the heating element <NUM> is contemplated for use in the column heating apparatuses <NUM>, <NUM> of the representative embodiments described in connection with <FIG>.

The heating element <NUM> is illustratively a resistive heating element, such as a wire heater or a foil heater. Other types of heating elements are contemplated. As should be appreciated, the heating element <NUM> is beneficially quite thin, and thereby does not substantially interfere with the desirably flat nature of each of the layers of the column heating apparatus <NUM>. The heating element <NUM> may be of any substantially planar shape, including non-uniform shapes. With known thin film fabrication methods, such comparatively thin heating elements that are within the purview of one of ordinary skill in the art are contemplated.

The column heating apparatus <NUM> also comprises second substrate <NUM> disposed over the heating element <NUM>. The second substrate <NUM> is configured to be in thermal contact with the GC column <NUM> (not shown in <FIG>), which may comprise direct contact with the upper surface <NUM> or with a substantially close proximity to the upper surface <NUM> to transfer heat from the column heating apparatus to the GC column <NUM>. In embodiments, the GC column <NUM> may be in thermal contact with the second substrate <NUM> despite an intervening layer (not shown) between the GC column <NUM> and the second substrate <NUM>. Illustratively, the GC column is disposed over an upper surface <NUM> of the second substrate <NUM>, and heat from heating element <NUM> is transferred through the second substrate <NUM> as described above in connection with the representative embodiments of <FIG>. The first and second substrates <NUM>, <NUM> may comprise single layer or multiple layers of the same or different materials. Through the heat distribution of the second substrate <NUM> described above, the apparatus <NUM> substantially uniformly heats the GC column contacting the second substrate <NUM>.

<FIG> shows an isometric partial cutaway view of a column temperature control apparatus <NUM> (sometimes referred to as "an apparatus") for heating and cooling a GC column <NUM> in accordance with a representative embodiment. Many aspects of the column temperature control apparatus <NUM> are substantively the same as those described above in connection with the representative embodiments of <FIG>, and will not be repeated in order to avoid obscuring the description of the column heating and cooling apparatus <NUM>.

The column temperature control apparatus <NUM> comprises a housing <NUM>, which has an interior portion <NUM>. The housing <NUM> is configured to hold column heating apparatus <NUM>, or the column heating apparatus <NUM> in its interior portion. Generally, the housing <NUM> can be made of one or more of a number of materials that are compatible with the thermal requirements of the column heating and cooling apparatus <NUM>. For example, the housing <NUM> comprises a metal or metal alloy, or thermally suitable polymeric materials. Notably, as described more fully below, a first actuator <NUM> and a second actuator <NUM> are configured to move a first thermal insulation layer <NUM> and a second thermal insulation layer <NUM> to be in contact with and out of contact with the outer sides of the column heating apparatus <NUM> and the GC column <NUM>. These thermal insulation layers at least have the ability to insulate the column and column heater from heat loss, but may also have additional insulative properties as would be appreciated by those skilled in the art. Illustratively, the outer sides of the column heating apparatus <NUM> include the upper surface <NUM> of the second substrate <NUM>, and the lower surface (i.e., the surface opposing the upper surface <NUM>) of the first substrate <NUM>.

As described more fully below, the first actuator <NUM> (as indicated by arrows <NUM>) and the second actuator <NUM> (as indicated by arrows <NUM>) are each configured to move inwardly before a heating cycle begins in order to maintain the first and second thermal insulation layers <NUM>, <NUM> in comparatively firm contact with the outer surfaces of the column heating apparatus <NUM> and the GC column <NUM>; and are configured to move outwardly (again, as indicated by arrows <NUM>, <NUM>) after a heating cycle ends and before a cooling cycle begins in order to separate the first and second thermal insulation layers <NUM>, <NUM> from the outer surfaces of the column heating apparatus <NUM> and the GC column <NUM>. Notably, in <FIG>, the first actuator <NUM> and the second actuator <NUM> shown in their inward-most position and thereby the first and second thermal insulation layers <NUM>, <NUM> are in comparatively firm contact with the outer surfaces of the column heating apparatus <NUM>. As such, in <FIG> the various components of column heating and cooling apparatus <NUM> are positioned for a heating cycle.

The column heating and cooling apparatus <NUM> also comprises a fan <NUM> situated to provide airflow in the interior portion <NUM> during a cooling cycle. The fan <NUM> may comprise a single fan or multiple fans to direct airflow in the interior portion. Note that while the fan or fans are configured to blow air over the column heating apparatus <NUM>, they could also be configured to pull air over the column heating apparatus <NUM>. Notably, the fan <NUM> may be oriented in a manner perpendicular to the orientation depicted in <FIG> and this can direct flow perpendicular to the direction of flow of <FIG>.

The first and second thermal insulation layers <NUM>, <NUM> are made of a material suitable to provide ample thermal insulation without interfering with the performance of the GC system. Illustratively, the first and second thermal insulation layers <NUM>, <NUM> are made of a glass fabric material having a thickness of approximately <NUM> in. , and can be provided as "blankets" to improve conformance of the first and second thermal insulation layers <NUM>, <NUM> to the outer surfaces of the column heating apparatus <NUM> with which they contact. Alternatively, the first and second thermal insulation layers <NUM>, <NUM> may comprise other types of insulation including, but not limited to fiberglass, glass cloth, basalt, and the like. The material selected for the first and second thermal insulation layers <NUM>, <NUM> generally needs to provide a sufficient thermal barrier between the column heating apparatus <NUM> and the ambient environment during a GC run, while being capable of being cooled comparatively thoroughly and quickly after the GC run.

As noted above and as described more fully below, the first and second actuators <NUM>, <NUM> are configured to engage the first and second thermal insulation layers <NUM>, <NUM> to be in comparatively good thermal contact with the outer surfaces of the column heating apparatus <NUM> during a heating cycle, and to create a space of separation between the first and second thermal insulation layers <NUM>, <NUM> and the column and outer surfaces of the column heating apparatus <NUM> during a cooling sequence. The first and second actuators <NUM>, <NUM> may be one of a number of known mechanical actuators that are configured to move the first and second thermal insulation layers <NUM>, <NUM>. The movement of the first and second actuators <NUM>, <NUM> to engage and separate the first and second thermal insulation layers <NUM>, <NUM>, may be mechanical, pneumatic, magnetic, manual, or may be through electrical control. Moreover, while two actuators are shown, it is noted that more or fewer actuators are contemplated by the present teachings to effect the movement of the first and second thermal insulation layers <NUM>, <NUM> through direct or indirect motion system (e.g., a cable and pulley system).

<FIG> shows a cross-sectional view of the column heating and cooling apparatus <NUM> in accordance with a representative embodiment. Again, many aspects of the column heating and cooling apparatus <NUM> are substantively the same as those described above in connection with the representative embodiments of <FIG>, and will not be repeated in order to avoid obscuring the description of the column heating and cooling apparatus <NUM>.

In <FIG> the first actuator <NUM> and the second actuator <NUM> are shown in their inward-most position (as indicated by arrows <NUM>, <NUM>, respectively), and thereby, the first and second thermal insulation layers <NUM>, <NUM> are in comparatively firm contact with the outer surfaces of the column heating apparatus <NUM>. As such, in <FIG> the various components of column heating and cooling apparatus <NUM> are positioned for a heating cycle. As described below, the pressure of the first and second thermal insulation layers <NUM>, <NUM> ensures good thermal contact between the GC column <NUM> and the outer surfaces of column heating apparatus <NUM>, which aids to improve retention time repeatability, cycle time, and energy efficiency.

The engagement of the first and second thermal insulation layers <NUM>, <NUM> with the outer surfaces of the column heating apparatus <NUM> usefully improves thermal efficiency by reducing the loss of thermal energy to the ambient environment. The first thermal insulation layer <NUM> also provides protection of the GC column <NUM> from the ambient environment. Notably, the first thermal insulation layer <NUM> provides a thermal break from the ambient environment and thus reduces the susceptibility of the GC column to the temperature of the ambient environment, which can be an uncontrolled environment. Similarly, although less directly, the second thermal insulation layer <NUM> also provides protection of the GC column <NUM> from the ambient environment by providing substantial thermal isolation of the first substrate <NUM>(not shown in <FIG>) from the ambient environment.

As such, the engagement of the first and second thermal insulation layers <NUM>, <NUM> results in faster heating of the GC column <NUM>, and the use of less energy to reach a certain temperature compared to certain known GC column heaters. The first and second actuators <NUM> and <NUM> are configured to be set in positions to be fully engaged (i.e., so that the first and second thermal insulation layers <NUM>, <NUM> are in contact with the GC column <NUM> and column heating apparatus <NUM>) or fully disengaged (i.e., so that the first and second thermal insulation layers <NUM>, <NUM> are not in contact with the GC column <NUM> and column heating apparatus <NUM>). In addition, the first and second actuators <NUM> and <NUM> can be asymmetrically positioned. For example, first actuator <NUM> may be moved away from column heating apparatus <NUM> while second actuator <NUM> is fully engaged with column heating apparatus <NUM>. For GC applications where the heater assembly <NUM> (not shown in <FIG>) of column heating apparatus <NUM> is operated near ambient temperature or at isothermal temperatures, temperature control can be improved by having a cooling flow over column heating apparatus <NUM> or over first and second thermal insulation layers <NUM>, <NUM> in contact with column heating apparatus <NUM> and GC column <NUM>. To achieve this, either or both of the first and second thermal insulation layers <NUM>, <NUM> can be moved a small distance apart from GC column <NUM> and column heating apparatus <NUM> or left in contact with them. The fan <NUM> can be turned at maximum power, run under proportional power control, or turned off to allow variable amounts of cooling air to move across the GC column <NUM> and column heating apparatus <NUM>.

Finally, although not forming part of the claimed invention, it is noted that the first and second thermal insulation layers <NUM>, <NUM> may be foregone, and the column heating and cooling apparatus <NUM> may function in a heating cycle without them, while using the fan <NUM> during the cooling cycle as described below. This option, although possible, is less beneficial than the representative embodiments comprising the first and second thermal insulation layers <NUM>, <NUM> configured to engage the column heating apparatus <NUM> during a heating cycle as described above. Most notably, in such an apparatus where the first and second thermal insulation layers <NUM>, <NUM> are foregone, the rate of heating of the GC column <NUM> is adversely impacted, and the general repeatability of the GC column <NUM> suffers as the GC column <NUM> and the column heating apparatus <NUM> are more susceptible to changes in the ambient environment.

In <FIG> the first actuator <NUM> and the second actuator <NUM> are shown in their outward-most positions (as indicated by arrows <NUM>, <NUM>, respectively), and thereby, the first and second thermal insulation layers <NUM>, <NUM> are separated from the outer surfaces of the column heating apparatus <NUM>. As such, in <FIG> the various components of column heating and cooling apparatus <NUM> are positioned for a cooling cycle. As described below, the removal of the first and second thermal insulation layers <NUM>, <NUM> from contact with the column heating apparatus <NUM> improves the efficiency of cooling during the cooling cycle, increasing both the rate and completeness of the cooling. Beneficially, not only is the cooling rate increased, which results in an improvement in the cycle time, but also the removal of latent heat is improved enabling a comparatively high repeatability of the retention time of a particular analyte.

With the separation of the first and second thermal insulation layers <NUM>, <NUM> from the outer surfaces of column heating apparatus <NUM>, a plurality of channels <NUM> are created between the inner surfaces of the first and second thermal insulation layers <NUM>, <NUM> and the column heating apparatus <NUM>. First and second outer channels <NUM>, <NUM> respectively exist in the housing on the outer surfaces of the first and second thermal insulation layers <NUM>, <NUM>. During operation, the fan <NUM> is engaged and air (indicated by arrows <NUM>) from the fan flows in the channels <NUM>, and the first and second outer channels <NUM>,<NUM>, to remove thermal energy by forced convection from the region surrounding the column heating apparatus <NUM>. By separating the first and second thermal insulation layers <NUM>, <NUM> from the column heating apparatus <NUM> as shown in <FIG>, the air flows over not only the outer surfaces of the column heating apparatus <NUM>, but also over both sides of each of the first and second thermal insulation layers <NUM>, <NUM> efficiently removing residual heat that could otherwise be trapped in the column heating and cooling apparatus <NUM>. For example, if the first and second thermal insulation layers <NUM>, <NUM> remained in their engaged position in contact with the outer surfaces of column heating apparatus <NUM> (e.g., as shown in <FIG> and <FIG>) the air flow during a cooling cycle would only flow over the outer portions of the first and second thermal insulation layers <NUM>, <NUM> (i.e., only in the first and second outer channels <NUM>,<NUM>), and not through inner channel <NUM>. As such, the air would not flow over the outer surfaces of column heating apparatus <NUM> or over the inner surfaces of the first and second layers of insulation <NUM>, <NUM>. While cooling would be improved over many known GC heater devices, the likelihood of residual heat in regions not flushed with air flow from the fan <NUM> would be increased (i.e., as depicted in <FIG>) compared to the representative embodiment in which the first and second thermal insulation layers <NUM>, <NUM> are separated from contact with the outer surfaces of column heating apparatus <NUM>. This residual heat would increase the cycle time, and if removed insufficiently could decrease the repeatability of the retention time of a particular analyte. In addition, the first and second thermal insulation layers <NUM>, <NUM> could be moved until they contact the housing <NUM>, increasing the space between column heating apparatus <NUM> and first and second thermal insulation layers <NUM>,<NUM>. While cooling would be improved over many known GC heater devices, the likelihood of residual heat in regions not flushed with air flow from the fan <NUM> would be increased compared to that attained via the representative embodiment in which the first and second thermal insulation layers <NUM>, <NUM> are separated from contact with the outer surfaces of column heating apparatus <NUM> (i.e., as depicted in <FIG>). This residual heat would increase the cycle time, and if removed insufficiently could deleteriously decrease the repeatability of the retention time of a particular analyte. An additional construct is to move only one of the insulation pads away from column heating apparatus <NUM>. Air flow across the exposed side of column heating apparatus <NUM> (likely first substrate <NUM>) would permit cooling without exposing the GC column <NUM> interfaced with second substrate <NUM> to cooling air flow. Such a configuration may allow improved retention time stability at near ambient temperatures.

Claim 1:
An apparatus comprising:
a housing configured to receive a planar column heating apparatus;
a planar column heating apparatus comprising a first side and a second side, and a heater assembly disposed within the first side and the second side;
a first thermal insulation layer adjacent to the first side;
a second thermal insulation layer adjacent to the second side; and
an actuator connected to the housing and configured to move the first and second thermal insulation layers in contact with the first and second sides of the planar column heating apparatus, respectively, during a heating sequence, and to move the first and second thermal insulation layers out of contact with the first and second sides of the planar column heating apparatus, respectively, during a cooling sequence.