Abstract:
A trans-configurable modular chromatograph assembly is provided with a core unit, at least one column module, and at least one detector module. The core unit includes a controller module having a first computer processing unit, an analogue to digital signal converter, and a thermally insulated enclosure. The enclosure includes a first heater member positioned to heat the thermally insulated first enclosure housing, a first analytes stream inlet, and a first analyte stream conduit. A temperature controller is programmed to maintain the thermally insulated first enclosure at a uniform temperature throughout an analysis. The at least one column module includes a computer processor, means for releasably securing the core unit to a column module, a capillary column, a capillary column heater member, and means for sensing and controlling the temperature of the capillary column. The capillary column has an analyte outlet member in fluid communication with at least one detector module. The at least one detector module has a computer processing unit, and an analogue to digital signal converter, means for releasably securing said core unit to the detector module. The detector module includes detector member within a thermally insulated enclosure.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of pending patent application Ser. No. 12/555,783, filed Sep. 8, 2009, published as PCT/US2009/056281 on Mar. 11, 2010, and having the title, “Fast micro Gas Chromatograph System”, the disclosure of which is incorporated by reference, as though recited in full. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a modular chromatograph system having a core unit, and at least one self-supporting column module and at least one self supporting detector module. 
     BACKGROUND OF THE INVENTION 
     Summary of the Invention 
     The present invention relates to a trans-configurable modular chromatograph. The term “trans-configurable”, as employed herein, refers to a chromatograph that is composed of a plurality of self-supporting components. The configuration of the chromatograph can be changed by adding a component, or components, removing one or more components, or interchange one type of component for another type of component. Thus, the trans-configurable modular chromatograph is not merely assembled from a plurality of modular components, but can be reassembled to produce a new configuration. 
     In an embodiment of the invention, the chromatograph includes a core unit, at least one column module, and at least one detector module. The term “core unit” as employed herein, refers to the component of the chromatograph that is common to all configurations of the gas chromatograph modular system. The core unit is the substrate upon which a complete system is built. A complete system includes at least the core unit, one column module, and one detector module. It should be noted that a plurality of columns, detectors, or other equipment can be employed. 
     In accordance with the present invention, the chromatograph includes a core unit, and one column module, and one detector module, or a plurality of column modules and a plurality of detector modules, or one column module and a plurality of detector units, or a plurality of column modules and one detector module, etc. 
     In accordance with an embodiment of the invention, the core unit includes a controller module which includes a first computer processing unit, which has computer processor, computer memory, plurality of digital signal input/output ports, alpha-numeric character displaying member, and an analogue to digital signal converter. The core unit further includes a thermally insulated first enclosure. Within the thermally insulated first enclosure there is a first heater member, which is positioned to heat the interior of the thermally insulated first enclosure housing, and components within the enclosure. The components within the enclosure can include a heater, an injector, a first analytes stream inlet, a first analyte stream conduit, a stream switching mechanism, and a fan. Additionally, the core unit includes a temperature controller, which controls the heater member and is programmed to maintain the thermally insulated enclosure at a uniform temperature throughout an analysis. 
     In accordance with an embodiment of the invention a first column module includes a first computer processing unit having means for releasably securing the core unit to the first column module, capillary column, a capillary column heater member, a capillary column analyte inlet member, a capillary column analyte outlet member, and means for sensing and controlling the temperature of the capillary column. The capillary column analyte outlet member is in fluid communication with at least one detector module, and first computer processing unit includes a computer processor, computer memory, and a plurality of digital signal input/output ports. 
     In accordance with another embodiment of the invention a first detector module, includes a first computer processing unit, the first computer processing unit having means for releasably securing the core unit to the first detector module, a detector member, a detector member analyte inlet member, and a thermally insulated enclosure. The detector member is mounted within the thermally insulated enclosure, and the first computer processing unit includes a computer processor, computer memory, a plurality of digital signal input/output ports, and analogue to digital signal converter. The capillary column analyte outlet member is in fluid communication with the detector module inlet member. 
     In accordance with a further embodiment of the invention a plurality of the first detector module&#39;s first computer processing unit&#39;s plurality of digital signal input/output ports are in digital signal communication with a plurality of the core unit&#39;s first computer processing unit&#39;s plurality of digital signal input/output ports, and a plurality of the first column module&#39;s first computer processing unit&#39;s plurality of digital signal input/output ports are in digital signal communication with a plurality of the core unit controller module&#39;s plurality of digital signal input/output ports. 
     In accordance with another embodiment of the invention means is provided within the thermally insulated first enclosure for switching stream flow from the first analyte stream conduit to and between at least one column module and at least one detector module is a cross fluid connector. The means for switching stream flow from the first analyte stream conduit to and between at least one column module and at least one detector module can be an electromechanical or pneumato-mechanical switch, a Dean&#39;s switch, or any other switching mechanism as now or hereinafter known in the art. 
     In accordance with a further embodiment of the invention a trans-configurable modular chromatograph includes a core unit first heater member with a plurality of parallel radiation fins or holes and heating means for heating the plurality of parallel radiation fins or holes, and a fan member. The fan member is within the core unit thermally insulated first enclosure, and being positioned to distribute heat within the thermally insulated first enclosure housing. The heater serves to isothermally heat the first analytes stream inlet, the first analyte stream conduit and any other component that is within the thermally insulated first enclosure, such as a stream switching member and an injector. 
     In accordance with a still further embodiment of the trans-configurable modular chromatograph of the present invention, the core unit includes a core unit thermally insulated first enclosure which comprises an outer sheet metal enclosure, insulating means, and an inner sheet metal enclosure, and insulating means enclosed between the outer sheet metal enclosure and the inner sheet metal enclosure. 
     In accordance with a still further embodiment of the trans-configurable modular chromatograph of the present invention, the column module includes a capillary column that is spirally wound on a ring support. A thermal resistive member is substantially coextensive with the column, and the thermal resistive member and the column member are enclosed within a sheath member. A controller is provided for maintaining the thermal resistive member at a temperature equal to or above the maximum column operating temperature. The ring member is preferably aluminum or copper. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a plan view of a modular assembly having one self-supporting detector module and one self-supporting column module in accordance with the invention; 
         FIG. 2  is a plan view of a modular assembly having a first detector module, a column module and a second detector module in accordance with the invention; 
         FIG. 3  is a plan view of a modular assembly having a first detector module, a first column module and a second column module in accordance with the invention; 
         FIG. 4  is a plan view of a modular assembly having a first detector module, a first column module, a second detector module and a second column using a Y connector between the two columns, in accordance with the invention; 
         FIG. 5  is a plan view of a modular assembly having a first detector module, a first column module, a second detector module and a second column using a switching valve between the two columns, in accordance with the invention; 
         FIG. 6  is a plan view of a modular assembly having a first detector module, a first column module, a second detector module and a second column using a Dean&#39;s switch between the two columns, in accordance with the invention; 
         FIG. 7  is a perspective view of the electronics area of the core unit in accordance with the present invention; 
         FIG. 8  is a perspective view of the core unit illustrating the isothermal oven, heating element, fan, cross stream splitter, and injector, in accordance with the invention; 
         FIG. 9  is a perspective view of the interior of the column module, without the column, in accordance with the invention; 
         FIG. 10  is a perspective view of a column module with lid and fan, in accordance with the invention; 
         FIG. 11  is a perspective view of a lid and fan of a column module, in accordance with the invention; 
         FIG. 12  is a perspective view of a capillary column, including an RTD wire, and a sheath enclosing the capillary column and the RTD wire. 
         FIG. 13  is a perspective view of a cylindrical mounting ring and capillary column, including end heaters, including a fragmentary view of one of the end heaters, in accordance with the invention; 
         FIG. 14  is a fragmentary perspective view of a column module, in accordance with the invention; 
         FIG. 15  is a schematic illustration of wiring for a capillary column and the capillary column end heaters in accordance with the invention; 
         FIG. 16  is a perspective view of a detector module including pneumatic and electronic sub-modules in accordance with the invention; 
         FIG. 17  is a schematic illustration of wiring and plumbing lines for a core unit in accordance with the invention; 
         FIG. 18  is a schematic illustration of wiring and plumbing lines for a detector module in accordance with the invention; 
     
    
    
     DETAILED DESCRIPTION 
     It is advantageous to define several terms before describing the invention. It should be appreciated that the following definitions are used throughout this application. 
     Definitions 
     For the purposes of this disclosure, the term “analyte” shall refer to a substance or chemical constituent that is determined in an analytical procedure, such as a titration. An analyte (in analytical chemistry preferentially referred to as component) itself cannot be measured, but a measurable property of the analyte can. 
     For the purposes of this disclosure, the term “O.D” shall refer to outer diameter 
     For the purposes of this disclosure, the term “I.D” shall refer to inner diameter 
     For the purposes of this disclosure, the term “FID” shall refer to Flame Ionization Detector 
     For the purposes of this disclosure, the term “FPD” shall refer to Flame Photometric Detector 
     For the purposes of this disclosure, the term “TCD” shall refer to Thermal Conductivity Detector 
     For the purposes of this disclosure, the term “SPU” shall refer to Sample Processing Unit 
     For the purposes of this disclosure, the term “EPC” shall refer to Electronic Pressure Control 
     For the purposes of this disclosure, the term “VSO” shall refer to Voltage Sensitive Orifice 
     For the purposes of this disclosure, the term “RSD” shall refer to Relative Standard Deviation 
     For the purposes of this disclosure, the term “RTD” shall refer to Resistance Temperature Device 
     For the purposes of this disclosure, the term “VOC” shall refer to Volatile Organic Carbon 
     For the purposes of this disclosure the term “core unit” refers to the assembly that is common to modifications of the gas chromatograph modular systems. It is the substrate upon which a complete system is built. A complete system includes at least the core unit, one column module, and one detector module. It should be noted that additional columns, detectors, or other equipment can be employed. 
     Self-Supporting Modular Components 
     The disclosed gas chromatograph (“GC”) comprises at least three modules, each being electronically and mechanically, self-supporting. The primary module is a sample processing unit, and the secondary modules are one or more column modules and detector modules. The modular system provides for additional modules to be added as necessary or worn out modules replaced without rebuilding the entire system. 
     Examples of the versatility of the modular assembly  100  are illustrated in  FIGS. 1-6 . As will be illustrated, the modular assembly system  100  can contain one or a plurality of column modules. In a two column module system, for example, each module can have the same conductive capillary column type (e.g. two 180 μm ID, MXT-1 liquid phase coatings) or can be different (e.g. one 180 μm ID, MXT-1 liquid phase coating and one 320 μm ID, MXT-Alumina coating). This powerful use of two different conductive capillary column types in the same GC system, on the same injected sample, enable the shortcomings of the first column material to be met by the second and vice versa. For example, one column can be optimum for separation of one or more components from the feed stream while the other column can be optimum for separation of another component, or components from the feed stream. In  FIG. 1  the assembly  100  contains a first detector module  102  and a first column module  104  which are in communication through conduit  126 . An injector  120  is connected to the first column module  104  through conduit  122 . In this configuration a single sample would be injected into column  104  and analyzed in detector  102 . 
     In  FIG. 2  a second detector module  108  has been added and is connected to the first column  104  through Y connector  200 , and conduits  228  and  226 . In this configuration the sample is injected directly through injector  120  into first column module  104 . The first column module  104  is connected to the Y  200  through conduit  226  from which conduits  228  and  227  lead to second detector  108  and first detector  102  respectively. The use of dual detectors permits the identification of additional analytes. The flow into the two detectors can be sequential corresponding to different separation times of components coming through the capillary column  104 . 
     In  FIG. 3 , the injector  120  is, through conduit  124 , attached to a second column module  106  which is, through conduit  324 , connected directly to the first column module  104 . The analytes injected into the second column module  106  which then sends the analytes to the first column module  104  which are then sent to first detector module  102  through conduit  322 . The dual column design enables higher degrees of separation in that one column is specific for the separation of first sub-groups of components and the other column is specific for the separation of the first sub-group into further sub-groups. 
     The combination in  FIG. 4  illustrates the injector  120  connected to a Y connector  200  through conduit  420  and, through conduits  426  and  424  into first column module  104  and second column module  106  respectively. The first column module  104  is connected to first detector module  102  through conduit  322  and the second column module  106  to second detector module  108  through conduit  422 . In this manner, there are two levels of component separation and individual detection for each of the two levels of separation. 
     In  FIG. 5  the first column module  104  and second column module  106  are used along with first detector  102  and second detector  108 , as illustrated in  FIG. 4 . In this figure, a switch  500  is used to add the ability to control the path of the analytes. The injector  120  is connected directly to the first column module  104  through conduit  522 . From the first column module  104  the analytes enter the switch  500  through conduit  526 . From the switch  500  the analytes can be directed through conduit  524  to column module  106  or to first detector  102  through conduit  528 . From second column module  106 , the analyte passes through conduit  422  to second detector  108 . In this embodiment conduit  540  is illustrated to feed an auxiliary carrier gas into the switch  500 . 
     In  FIG. 6  the arrangement is the same as in  FIG. 5  with the exception of a Dean&#39;s switch  600  being used. Therefore, the injector  120  injects the analyte into first column module  104  through conduit  522  where it enters the Dean&#39;s switch  600  through conduit  626 . From the Dean&#39;s switch  600  the analyte can enter either second column  106  through conduit  624  or first detector  102  through conduit  628 . Analyte entering second column module  106  exits to second detector  108  through conduit  422 . The auxiliary carrier gas conduit  640  feeds into the Dean&#39;s switch  600  for dispersal as described above. 
     The embodiments of  FIGS. 5 and 6  are designed for use when two or more analytes have the same separation time through first column module  104 . For example a first analyte exits first column module  104  and is directed into first detector module  102 . Switch  500  or  600  is activated to send two or more analytes having the same separation time through the first column module to a second column module  106  for further separation and then to the second detector  108 . Switch  500  or  600  can then be deactivated to direct other analytes from first column module  104  to first detector module  102 . This heart cut technique is only one of a suite of techniques known as column switching to those skilled in the arts. Simple valve and plumbing implementations within the isothermal oven  803  enable back flush, bypass, trap/bypass, etc. 
     It should be noted that although only one detector module and one column module will be referred to hereinafter, this is not to limit the scope of the invention but rather to make the description more readable. 
     Sample Processing Unit 
     The modular components are physically arranged around the centrally located Sample Processing Unit (SPU)  800  as illustrated in  FIG. 7 , and which serves as the core unit for the modular assemblies as illustrated in  FIGS. 1-6 . The SPU  800  contains an isothermal oven compartment as best viewed in  FIGS. 7 and 8 , which houses the injection port inlet  832 , injection port  120 , cross stream splitter  914  fan  902 , heater radiation fins  908 , and thermal insulation  904 . The interior components are housed within a sheet metal frame  906 . An electro-pneumatic compartment  801 , as best seen in  FIG. 7 , contains electronic pressure controllers/flow controllers  826 , on/off solenoid valves  810 ,  820 ,  821 , septum purge needle valve  822 , and split-vent needle valve  824 , as well as any additional optional equipment, needed for proper pneumatic functioning of the GC system  100 , the SPU circuit board  817  which controls the aforementioned components, as well as the SPU heater circuits. 
     The components are enclosed within a chassis, preferably formed of single sheet of metal, having sides  812 ,  814 ,  815 ,  816  and  813  that are bent to form wings  812  and  813  that are provide with detector mounting holes  802  and the PCB mounting stud  804 . The pneumatics mounting plate  819  serves as a mount board. Construction of the chassis will be known to those skilled in the arts. To prevent overheating of the components, air circulation vents  806  are provided in both of the sides  814  and  816 . Adjacent to the air circulation vents  806  is the wire harness through hole  808 . Although placed adjacent the air circulation vents  806 , the wire harness through hole  808  can be place along one of the sides  814 ,  816  at any place convenient for the interior arrangement. In the bottom portion of the SPU  800  is a thermal insulation through hole  818 . 
     Adjacent to the electro-pneumatic compartment  801  is the heating compartment  803 , the interior of which is shown in  FIG. 8 , which operates as an isothermal oven. The heating compartment has insulated sides  834  and  836  and a cover (not shown). Housed within the isothermal oven  803  are components that must be maintained at a constant, precise, elevated temperature relative to ambient. The SPU isothermal oven  803  preferably contains a finned or other high surface area heat sink  908 , to which a heater is attached. The SPU isothermal oven  803  can also contain a mixing fan  902  for distributing heat evenly throughout the oven as well as a switching mechanism such as switch  500  or  600 , splitter or cross stream splitter  910 , as shown in  FIG. 8  and described heretofore in  FIGS. 5 and 6 . Passages are provided for the end heater components described in detail hereinafter. The end heaters are inserted in the direction indicated by arrow  900 . 
     The SPU isothermal oven  803  contains the sample injection port  120  that has an internal glass liner used for sample introduction in either a user selectable split or splittless mode. The injection port  120  also contains a recess where a replaceable sealing septum resides. A metal cap holds the septum in place and provides an opening whereby a needle can be inserted for the purpose of injecting sample into the inner space of the injector glass liner. 
     The isothermal oven  803  is lined with insulation  904  between the interior wall  906  and exterior walls  834 ,  834 , top  836  and bottom (not shown). In this illustration the cross stream splitter  914  is shown, however any splitter or switching valves used, whether or not illustrated herein, would be located within the isothermal oven  803 . 
     The SPU isothermal oven  803  can contain transfer and/or flow restricting tubes of various lengths and inside diameters which are in fluid communication with the injection port  120 , Column Modules  104  and  106 , Detector Modules  102  and  108  and stream splitting/switching devices. Tubes directly attached to Column Module inlet and outlet connectors are preferably non-conductive in order to electrically isolate the charged Column Module end connectors from the rest of the system. 
     The isothermal oven  803  and associated thermal insulation preferably contain slots  910 , for enabling column modules  104  and  106 , as seen in  FIGS. 9 ,  13 , and  14  to be inserted and removed from the GC system  100  with only one axis of movement as indicated by arrow  900 , after mounting hardware and the insulated lid are removed. The column module heated ends  1048  pass through the passageways as illustrated by arrow  900 , in  FIG. 8 . The passageways  910  are closed with insulation when the column module  104  and/or  106  is in place, in order to maintain the column ends in an isothermal environment. 
     Flow Restrictors  1903  and  1907 , as seen in  FIG. 17  are installed between the low volume splitter tee  1909  and the two columns in order to increase the system operating pressure above what would normally be needed to drive the correct linear velocity of the carrier gas through the short columns that are used. These restrictors are generally 50 um I.D. deactivated fused silica and are necessary for columns greater than 100 um in I.D. The relative restriction values of both restrictors (i.e. their lengths) must be exactly the same if flow rates through the two different columns are to be equal. 
     The separation column  104  is housed in a self-contained module which includes all of the electrical controls and hardware necessary for rapid temperature programming through the use of resistively heated metal capillary column material and cooling independent of the other modules in the instrument. The material can range in size from 100 um I.D. to 320 μm I.D. 
     Sample components introduced into the GC modular assembly  100  at the injection port  120  are transferred to uniquely designed “smart” column modules  104 , as shown in  FIG. 9 , for separation. At the heart of the column module  104  is a conductive capillary chromatography separation column  1034 , as shown in  FIG. 12 , which performs the physical separation of chemical components as they traverse its length and interact with the special coating on the inside of the capillary tube. 
     Several different types of conductive capillary columns exist and are well known in the art and the disclosed modular system  100  system can easily contain any of these conductive capillary column types. Typical variations include different internal coating types (e.g. liquid coatings and porous layer coatings), coating thicknesses, as well as different inside diameters (ID) of the conductive capillary tube up to and including  320  micrometer (μm) ID. Each conductive capillary column type has its own advantages as well as shortcomings depending on the chemical compounds one wishes to separate. Common suppliers include Restek&#39;s MXT metal capillary column material, Agilent&#39;s Prosteel metal capillary column material, Quadrex&#39;s Ultra-Alloy metal capillary column material, as well as, VICI Valco&#39;s nickel coated fused silica capillary column material. Aluminum clad fused silica capillary columns could be employed in a Column Module, but are generally avoided due to the thermal stress fractures that develop in the aluminum cladding during repeated temperature cycling. 
     Column modules  104  and  106  consist of a small enclosure  1004  with a lid  1010 , as shown in  FIGS. 9 and 11 . The lid  1010  and bottom  1011  contain layers of high temperature thermal insulation, preferably polyimide foam to retain the desired temperatures. A column coil support  1046  maintains the column coil assembly  1030  in position, as shown in detail in  FIG. 9 , and a column end connector attachment plate  1050 . 
     The column coil support  1046  is a low thermal conductivity material, preferably mica, or a fiberglass printed circuit board. Electrical contacts (not shown) are provided for the connection of resistance heater wire. 
     Attached to the top of the Column Module  104  is a lid  1010  with a centrally located exhaust hole  1022 , as illustrated in  FIGS. 10 and 11 . Thermal insulation  1020  is affixed to the inside surface of the lid  1010  and a small box fan  1024  is attached to the exterior surface over the exhaust hole  1022 . The box fan  1024  draws cool air in from perforations  1006  located around the periphery of the main column module  104  enclosure and through the exhaust hole  1022  located on the lid  1010 . This serves the purpose of rapidly cooling the column coil assembly  1030  of  FIG. 13  after a programmed temperature chromatographic analysis is performed. The end regions of the column  1032  are heated by coiled resistance heating wire  1048 , ( FIG. 13 ). 
     Attached to the bottom of the column module  104  on standoffs is a printed circuit board (PCB)  1012  containing a microprocessor. The column module  104  PCB  1012  electronic components serve to independently control the column module  104 &#39;s electronic functionality. This includes but is not limited to storing programmed temperature cycle parameters, calibration parameters, column module identification information, maximum temperature limits, and cycle counters. This also includes the feedback temperature control of the column coil assembly  1030 , control of the power to the column end heaters and on/off control of the cooling box fan  1024 . The column module PCB  1012  also communicates directly with the SPU PCB. 
     The column coil assembly  1030 , as shown in  FIG. 13 , contains a capillary bundle  1032  illustrated in detail in  FIG. 12 , made from an electrically conductive open tubular capillary chromatography column  1034 , and a RTD wire  1036  coated with a thin, high temperature insulating layer, preferably polyimide, arranged nominally in parallel and in intimate thermal contact with the capillary chromatography column  1034 . An insulating high temperature sheath  1038 , preferably made of fiberglass, tightly encases the capillary chromatography column  1032  and RTD wire  1034  into a single linear column bundle  1032 . 
     In order for rapid temperature programming to be possible, some form of temperature sensing must be incorporated very near to the metal column material that is being resistively heated. This is accomplished by inserting both the capillary chromatograph column  1034  and a very small diameter wire (˜0.002″ dia.) coated with electrically insulating, high temperature polyimide resin  1036  co-linearly into a high-temperature fiberglass sheath  1038 . The small diameter wire  1036  is then fitted with low resistance lead wires and used as a RTD device  1036  for the feedback control loop that provides the temperature modulation. Due to the intimate contact between the RTD wire  1036  and the capillary chromatograph column  1034  and the low mass of each, the thermal transport delay between the two is very small which results in a very fast, accurate control loop. 
     This results in the elimination of temperature gradients along the length of the capillary column bundle  1032  and consequently the ability to obtain maximum separating efficiency from the capillary column material. Also a part of the column coil assembly  1030  is a thin, conductive metal cylinder  1040  with externally raised edges onto which the linear column bundle  1032  containing the capillary column  1034  and RTD wire  1036  are wrapped in tight cylindrical coils  1042 , as shown in  FIG. 14 , holding the column bundle  1032  in a very uniform, compact geometry. The raised upper lip  1060  and lower lip  1062  keep the capillary bundle from slipping off the ring  1040 . The compact, cylindrical coils  1042  of the column coil bundle  1032  also aid in conserving heat during heating cycles due to adjacent coils  1042  being in thermal communication with one another, but simultaneously allow for rapid cooling of the coil assembly  1032  due to its narrow cross section. Electrical shorts between adjacent coils of the capillary bundle  1032  and the aluminum cylinder  1040  are avoided due to the high-temperature fiberglass sheath  1038  that covers the column material and sensor wire  1036 . The metal ring  1040  is preferably made of relatively low mass aluminum, but other high thermal conductivity metals can be used, such as copper and brass. 
     There are two factors that limit the maximum length of material that can be installed in a column module  104 . The first is the number of coils that can be physical wrapped compactly around the conductive metal ring  1040  in the space reserved for the column module  104  in the instrument design. The second is the maximum heating rate that is desired for a given length of column material. This is due to the relatively high resistance of the metal column material and Ohm&#39;s law. The basic trade-off reduces to longer columns having to be heated at lower maximum rates than shorter columns, simply because the amount of power that can be dissipated in the metal tube falls off linearly with increasing length. However, as column length increases slower heating rates become necessary to extract the maximum resolution from the column, so the trade-off is somewhat balanced. 
     An example ring tested on the prototype was approximately 3″ in diameter with a wall thickness of 0.025″. The high thermal conductivity of aluminum serves a very important function for the overall efficient heating of the column material by dissipating thermal “hot-spots” generated during heating thereby creating a more uniform temperature distribution along the length of the column material. The more uniform the temperature distribution is the more efficient are the resulting component separations. 
     Also a part of the column coil assembly  1030  are lengths of small, dense coils of heater wire  1048  that encircle the free ends of the column bundle  1032  which exit tangentially from the coil ring  1040 . These small heater coils  1048  comprise the column end heaters and are used to eliminate cold spots by providing supplemental heat to the free ends of the column coil bundle  1032 . The overall diameter of the small coils  1048  is nominally ⅛″ with the wire diameter being nominally 0.010″ and preferably made of a nickel-chromium alloy. The ends of the small coils  1048  are attached such that the individual adjacent coils of wire are expanded and slightly separated from one another preventing a short circuit from one coil to the next. 
     The column coil support member  1046  resides within the column module  104  enclosure and is comprised of two slotted sheets of material that is both thermally and electrically insulating and is preferably rigid mica sheet or printed circuit board sheet. The sheets are orthogonally interleaved to form a cross into which the column coil assembly  1030  rests. Where a printed circuit board is used, electrical lines can have junction points on the circuit board. 
     Each free end of the column coil bundle  1032  is joined both electrically and pneumatically to a separate column end connector  1052  that consists of an elongated “Z” shaped metal bracket with the end farthest from the column module  104  enclosure having a small pneumatic metal fitting  1054  attached, as shown in  FIG. 14 . The column end connectors  1052  are attached to the column end connector attachment plate  1050  which in turn is attached to one side of the column module enclosure  104 . The column end connector attachment plate  1050  is made from an insulating sheet, preferably rigid mica sheet or printed circuit board sheet, and serves to electrically isolate the conductive column material while providing extended mechanical support structures for the column coil bundle  1032  ends. The column end connectors  1052  are extended away from the column module  104  enclosure in order for them to protrude into the SPU isothermal oven of  FIG. 8 , thereby eliminating them as potential cold spots in the analytical flow path. 
     The capillary column ends are attached to the pneumatic metal fittings  1054 , with conductive metal ferrules (not shown). The metal ferrules both seal the column ends to the metal fittings  1054  pneumatically as well as provide electrical continuity between the conductive capillary bundle  1032  and the column end connectors  1052 . This enables the column end connectors  1052  to be used as electrical nodes for attaching lead wires from the column module PCB  1012 . Power is applied to these nodes to resistively heat the conductive capillary column  1034  and simultaneously the column end heaters  1048 . 
     The column end heaters  1048  attach to the column end connectors  1052  through the use of a specially designed column nut  1058 , which contains a threaded stud on one end. The small column end heater wire  1048  is threaded onto the column nut  1058  stud creating a mechanical and electrical connection to the column end connector  1052  node. The opposite ends of the column end heater wires  1048  are attached to the column coil support  1046  immediately adjacent to the point where the column bundle  1032  leaves the column coil cylinder  1040 . Lead wires attach to each column end heater wire  1048  at this point and plug into the column module PCB  1012  at their opposite ends. 
     With the sheathed column material  1034  tightly and compactly coiled on the aluminum support ring  1040 , a large reduction of surface area is created along the entire length of the column  1034 . This reduces convective heat losses and consequently the power required to heat the column  1034  at a given linear temperature ramp. However, the free ends of the sheathed column assembly  1030  that are not wrapped on the aluminum support ring  1040  have a much larger surface area per unit length of column material exposed to free convection that results in a lower temperature profile relative to the coiled main body of the column material. This differential temperature profile between the free ends and the main body is only exacerbated as the column main body temperature increases and can result in poor chromatography at column temperatures above ˜200 deg. C. 
     To alleviate this problem without implementing a separate actively controlled heater circuit to provide extra heat to the free ends, a heater circuit  1048  as show in  FIG. 15  was created that connects in parallel with the main heater circuit  1060 . The heaters  1048  can consist of pre-wound NiChrom wire coils purchased in bulk and then cut to the needed length. One end of the coil is attached to the end connector threaded nut while the other end connects to the insulating column support structure. The free ends of the column pass through the center of the heater coils  1048  thereby providing them with consistent, even heat along their entire length. 
     The heater coil  1048  ends that attach to the column support structure are connected to the column module PCB  1012 . As shown in  FIG. 15 , the PCB  1012  contains a transistor  1049  which, when activated, connects both end heaters  1048  together in series. Pulsing the transistor  1049 , or alternatively pulsing a switch  1068 , provides a means to control the current passing through each end heater and consequently the power dissipated in each. 
     Since the temperature of the coiled main column assembly  1042  body is actively controlled and the end heater coils  1048  are operated passively in parallel, the power dissipated in the end heater coils  1048  is proportional to the power dissipated in the main column assembly  1042  body based on the total series resistance of the end heater circuit. 
     The conductive capillary chromatograph column  1034  is thermally modulated through resistive heating by applying power directly to the column end connectors  1052 . The voltage applied to the column end connectors  1052  is precisely regulated by a PID negative feedback control loop implemented in the column module PCB  1012 . Due to the low thermal mass of the conductive capillary column  1034  and RTD sensor wire  1036 , as well as their intimate contact with one another, very accurate, fast linear temperature program ramps of the conductive capillary column are attainable from 0.05 deg. C/sec to 10 deg. C/sec. 
     Detector Modules 
     Detector modules  102  consist of independent, compact, self-contained subsystems that work in conjunction with the SPU  1012  and column modules  104  to perform a complete chromatographic analysis. Its ultimate function is to obtain intensity versus time characterization of the sample stream exiting the column module  104 ,  106  as it relates to the amount of mass per unit time or concentration of sample molecules that exist in the capillary column&#39;s mobile phase or carrier gas. 
     The detector module  102  contains all electronics and hardware necessary to convert a chemical signal from the effluent of a capillary separation column into a time-based digitized electrical signal where signal magnitude is proportional to chemical concentration. The electronics are capable of controlling heaters for isothermal ovens, pressure controllers or flow controllers for supply gases (e.g. hydrogen and air for a flame ionization detector), and signal transducer circuitry for converting an analyte molecular concentration or mass rate analogue data stream into a digitized data stream that can be recorded and ultimately used to quantify and/or identify chemical components. 
     An example detector module  2000 , as shown in  FIG. 16 , is constructed on a compact structural framework or chassis  2010  that can be internally compartmentalized with each compartment having sub-modules that attach to the chassis  2010  and fulfill a different functional requirement for the detector module  2000  as a whole. Each compartment sub-module can be easily inserted or removed from the main detector module  2000  chassis which greatly simplifies manufacturing assembly and part replacement in the field. 
     In this example of a complete detector module  2000 , flame ionization Detector Module  2000  can have a top level isothermal oven  2012  compartment containing the flame ionization mechanical components  2002  which must remain at a stable, elevated temperature relative to ambient for normal operation. Attached below the isothermal oven  2012  resides a pneumatic sub-module  2004  which contains electronic pressure or flow controllers supplying precise flows of hydrogen and air through small tubing to the above flame ionization mechanicals. Attached directly below the pneumatic sub-module  2004  sits the electronics sub-module  2006  that consists of a main microprocessor based PCB and an electrometer PCB. The main PCB controls the hydrogen and air pressure/flow controllers, the isothermal oven, the flame ionization ignition source and the electrometer auto-zero function. It also digitizes and conditions the signal received directly from the adjacent electrometer as well as communicates with the GC system communication PCB  1012 . 
     Several different types of chromatographic detectors exist and are well known in the art. Each detector type has its own advantages as well as shortcomings. Some of these detectors include flame ionization detectors (FID), thermal conductivity detectors (TCD), flame photometric detectors (FPD), electron capture detectors (ECD), pulsed discharge detectors (PDD), argon ionization detectors (AID), photo-ionization detectors (PID), plasma emission detectors, and various mass spectrometry detectors (MSD). Detector Modules in the GC system can contain any of these detector types provided that the mechanical and electrical components of the detector can be made to fit appropriately in the space available for the module. 
     As stated heretofore, the GC systems as described above can contain one or two detector modules. In a two detector module system, each module can be of the same type (e.g. two FID detectors) or can be different (e.g. one FID and one TCD). Again, this powerful use of two different detector types allows the shortcomings of the first detector to be met by the second and vice versa. With the ability to couple different detector types with different column types in the same GC system, the number and type of chemical compounds that can be separated and quantified in a single analysis is greatly expanded. 
     Some instrument configurations can contain two Detector Modules with different types of detectors (e.g. FID and FPD or FID and TCD) for a single Column Module where the effluent from the column is split between the two for simultaneous analysis. Example schematics are illustrated in  FIGS. 17 and 18 , however other connections, both electrical and physical, will be known to those skilled in the art. 
     The column module  1901  is connected by a tube  1993  through flow restrictor  1   1903  to split Y  1909 . A second column module  1905  is connected by a tube  1993  through flow restrictor  2   1907  to split Y  1909 . The split Y  1909  is connected by tube  1993  through the heated zone  1911  to the inlet  1913 . 
     The inlet  1913  is connected by tube  1993  to the N.O. valve column head pressure  1929  which is then connected to the ballast volume  1931 , which is then connected to the EPC  1933 , which is then connected to the carrier gas  1935 . The inlet  1913  is also connected to the split vent proportional valve  1917  which is then connected to the split vent needle valve  1919  which then goes to the vent  1921 . The inlet  1913  is also connected the N.O. valve septum purge  1923  which is connected to the septum purge needle valve  1925  which then goes to the vent  1927 . 
     The SPU PCB  1938  has a 12 V output proportional valve  1939  that is connected by wire  1995  to the EPC  1933 . The SPU PCB  1938  has an input pressure sensor (H2)  1941  that is connected to the EPC by wire  1995 . The SPU PCB  1938  has a 12 V output on/off  1943  connected to the N.O. valve column head pressure  1929  by wire  1995 . The SPU PCB  1938  has an output 24 V resistance heater  1945  that is connected to headed zone  1911 . The SPU PCB  1938  has an input RTD  1947  that is connected to RTD  1915  by wire  1995 . The SPU PCB  1938  has a 12 V output on/off  1949  connected to N.O. valve septum purge  1923  by wire  1995 . The SPU PCB  1938  has a 12 V output proportional valve (split vent valve)  1951  connected to the split vent proportional valve  1917  by wire  1995 . The SPU PCB  1938  has a 24 V output resistance heater connected to the spare heater  1937 . The SPU PCB  1938  has an input RTD  1955  connected to the spare heater  1937 . The SPU PCB  1938  has a 12 V output on/off  1957  and a 12 V output on/off (multi-event) device  1959 . 
     The communication PCB  1987  has an input contact closure in  1965 . The communication PCB  1987  has an output display bus  1967  connected to the display  1991 . The communication PCB  1987  has an output 12 V on/off  1969  that connects to the cooling fan (case)  1989 . The communication PCB  1987  has a 12 V output on/off spare  1971 . The communication PCB  1987  has an RS-485 (Det. Bus). The communication PCB  1987  has an RS-485 (main bus) connected to the SPU PCB  1938  RS-485  1961 , 24 V DC  1963  and 12 V DC  1964 . The communication PCB  1987  has a 12 V DC input  1977 . The communication PCB  1987  has an input/output RS-232  1979 . The communication PCB  1987  has an input/output Ethernet  1981 . The communication PCB  1987  has an output autosampler start  1983 . The communication PCB  1987  has an input contact closure in  1985 .