Abstract:
The present invention is an improvement to two-dimensional comprehensive gas chromatography. The improvement is a one valve switching modulator connecting the two separation columns. The valve includes either a two position eight-port valve or a two position twelve-port valve, and two transfer lines.

Description:
This application claims the benefit of U.S. Provisional Application 61/190,482 filed Aug. 29, 2008 and U.S. Ser. No. 11/716,325, filed Mar. 9, 2007 now U.S. Pat. No. 7,779,670. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a comprehensive two-dimensional gas chromatography system. In particular, the present invention relates to the modulator for such a system. 
     Comprehensive two-dimensional gas chromatography (GC×GC) is a powerful separation technique that provides the superior chromatographic type separation to a complex mixture. It is the most significant development in the gas chromatography technology area during recent years. The key to make a conventional GC into a comprehensive two-dimensional gas chromatography (GC×GC) is the modulation system. In the prior art, modulation is achieved by the trap and release mechanism called “thermal modulation”. This method of modulation for GC×GC requires coolants (liquid nitrogen or liquid carbon dioxide) to operate. It is relatively inconvenient and it creates difficulty in the coolant handling situation, especially in the remote location or in the manufacture plant environment. 
     SUMMARY OF THE INVENTION 
     The present invention is an improvement to a comprehensive two-dimensional gas chromatography system. This improvement is a valve switching modulation system that has been designed and built for a comprehensive two-dimensional gas chromatography (GC×GC). In one embodiment, this valve switching modulation system utilizes one eight-port two-position switching valve to achieve the modulation. The valve system includes two transfer lines. In another embodiment, the valve switching modulation system utilizes one twelve-port two-position switching valve. 
     The advantages of using valve modulation for comprehensive two-dimensional gas chromatography are: (1) easy to understand and operate; (2) no extra external resource required; (3) unit design with either one eight-port two-position switching valve or one twelve-port two-position switching valve is especially attractive because of the simplicity. However, it is relatively difficult to design the experimental conditions to achieve the comprehensive two-dimensional analytical separation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram of one embodiment of the valve modulation system of the present invention. 
         FIG. 2  shows a schematic diagram showing the flow of the fluid from the first column through the valve modulation system into the second column. 
         FIG. 3  shows a comprehensive two-dimensional gas chromatogram of heavy catalytic naphtha using the valve modulation system of the present invention. 
         FIG. 4  shows a comprehensive two-dimensional gas chromatogram of diesel using the valve modulation system of the present invention. 
         FIG. 5  shows a schematic diagram of another embodiment of the valve modulation system of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Comprehensive two-dimensional gas chromatography is a recent development in the gas chromatography technical area. This new technique provides higher resolution, better sensitivity, and larger peak capacity. However, this new technique requires a modulation unit to manage this two dimensional separation. Most modulation unit design utilizes thermal modulation based on the pulsed trap-release mechanism with cold-hot gas flow throw through the modulation unit. This type of modulation unit requires a coolant, such as liquid carbon dioxide or liquid nitrogen, to perform the trap function. 
     A. One Eight-Port Two-Position Switching Valve 
     The present invention uses a type of modulation unit design different from the thermal modulation, referred to as differential flow modulation, which is based on a switching valve and the secondary carrier gas flow to achieve the modulations function for comprehensive two-dimensional gas chromatography. The present invention is one eight-port two-position switching valve.  FIG. 1  shows the design of the switching valve. 
       FIG. 2  shows a diagram of the switching valve showing the flow of fluid from the first column through the valve modulation system to the second column. When the valve is in position A at the 1 st  or 2n+1 modulation period, the first column eluent is deposited in transfer line A and the eluent in transfer line B from the last modulation period is swept by the secondary carrier gas flow into the second column. In the next modulation period, the 2 nd  or 2n+2 period, the valve switches to position B. The first column eluent then deposited in transfer line B and the eluent in transfer line A from the last modulation period is swept by the secondary carrier gas flow into the second column. By repeating this valve switching process, the modulation function is achieved and the comprehensive two-dimensional separation can be accomplished. 
     This invention describes a method to perform a comprehensive two-dimensional gas chromatography separation based on one eight-port two-position switching valve as a modulation unit. The separation is demonstrated with two examples; one for gasoline range hydrocarbon stream separation and the other one for the diesel temperature range hydrocarbon stream separation. 
     Experimental Set-Up and Conditions 
     The GC×GC system consists of an Agilent 6890 gas chromatograph (Agilent Technology, Wilmington, Del.) configured with inlet, columns, and detectors. A split/splitness inlet system with a 100-tray autosampler is used. The two-dimensional capillary column system utilizes a weak-polar first column (BPX-5, 30 meter, 0.25 mm I.D., 1.0 μm film), (SGE Inc. Austin, Tex., USA) and a polar (Sol-Gel Wax, 3 meter, 0.53 mm I.D., 1.0 μm film), (SGE Inc. Austin, Tex., USA) second column. A two-position, eight ports, switching valves modulation assembly based on  FIG. 1  is installed between these two columns. The valve is electrical actuatored (VICI Valco Instruments Co. Inc., Houston, Tex., USA). The transfer line is a set of pre-cut 1/16 inch stainless steel tubing with 0.25 mmID and 30 cm length (Upchurch Scientific Inc. Oak Harbor, Wash., USA). The detector is a Flame ionization detector (FID) which comes with Agilent GC system. 
     After data acquisition, it was processed for qualitative analysis. The qualitative analysis converts data to a two-dimensional image that is processed by a commercial program “Transform” (Research Systems Inc. Boulder, Colo.). The two-dimensional image is further treated by “PhotoShop” program (Adobe System Inc. San Jose, Calif.) to generate publication-ready images.  FIG. 3  is the comprehensive two-dimensional gas chromatogram of the naphtha. 
     EXAMPLE 1 
     The Heavy Catalytic Naphtha Stream 
     The heavy catalytic naphtha stream used in this study is typical refinery streams boiling between 65° C. (150° F.) to 215° C. (420° F.) with carbon number from approximately C 5  to C 16 . 
     A 0.2 μL sample was injected with 50:1 split at 300° C. in constant column flow mode at 1.5 mL per minute. The oven is programmed from 36° C. with 2 minute hold and 3° C. per minute increment to 180° C. with 0 minute hold and with total run time 50 minutes. The secondary carrier gas is in constant flow at 100 mL per minute. The modulation period is 8 seconds. The sampling rate for the detector was 100 Hz.  FIG. 3  is the GC×GC chromatogram of the heavy catalytic naphtha stream. 
     EXAMPLE 2 
     The Diesel Stream 
     The diesel fuels used in this study are typical refinery streams boiling between 150° C. (300° F.) to 430° C. (800° C.) with carbon number from approximately C 9  to C 28 . 
     A 0.2 μL sample was injected with 50:1 split at 300° C. in constant column flow mode at 1.5 mL per minute. The oven is programmed from 36° C. with 2 minute hold and 3° C. per minute increment to 300° C. with 0 minute hold and with total run time 90 minutes. The secondary carrier gas is in constant flow at 100 mL per minute. The modulation period is 8 seconds. The sampling rate for the detector was 100 Hz.  FIG. 4  is the GC×GC chromatogram of the diesel stream. 
     B. One Twelve-Port Two-Position Switching Valve 
     The modulation system can also be built with one valve with at least twelve ports.  FIG. 5  shows a schematic diagram of valve modulation system including only one valve. The detailed modulation process is explained below:
     (1) When the valve is in the position X in one modulation period (as on the left side in  FIG. 5 )   (a) The eluent comes out of the first dimensional column and flows through port  1  and then passes through port  12  and deposits in transfer line B and through port  8  and port  9  to vent   (b) The secondary carrier gas flow enters port  3 , passes to port  2  and sweeps the eluent deposited in transfer line A during the last modulation period through port  6  to port  7  and to the second dimensional column   (2) In the next modulation period, the valves switches to position Y (as on the right side in  FIG. 5 )   (a) The eluent comes out from the first dimensional column and flows through port  1  then passes through port  2  and deposits in transfer line A and through port  6  and port  5  to vent   (b) The secondary carrier gas flow passes through port  11  to port  12  and sweeps the eluent deposited in transfer line B from the last modulation period through port  8  to port  7  and to the second dimensional column.   

     The modulation system can also be built on one valve with more than twelve ports but because of the extra loops and ports involved, it will not perform as simple and as well as one twelve port valve.