Comprehensive two-dimensional gas chromatograph and modulator for the chromatograph

Abstract

A modulator for simply providing fast and precise sampling of a chromatographic peak eluting from a first column into a second column of a comprehensive two-dimensional gas chromatograph, where the modulator includes a planar component containing a first gas passage for connecting a carrier gas source to the second separation column, a second gas passage for connecting the first separation column to an exhaust outlet, a connecting gas passage between the first and second gas passages, and two individually controllable open/close valves arranged in parallel connection in the first gas passage between its connection to the carrier gas source and the branch-off of the connecting gas passage, and where the gas passages and valves are formed in the planar component by micromachining.

Claims

1. A comprehensive two-dimensional gas chromatograph, comprising: a first separation column; a second separation column; and a modulator controlled by a controller for sampling a chromatographic peak eluting from the first separation column into the second separation column; wherein the modulator comprises: a planar component including: a first gas passage having a first inlet end to which a carrier gas source is connected and a first outlet end to which the second separation column is connected; a second gas passage having a second inlet end to which the first separation column is connected and a second outlet end; a connecting gas passage between the first and second gas passages; and two individually controllable open/close valves arranged in a parallel connection in the first gas passage between the first inlet end and a branch-off point of the connecting gas passage from the first gas passage, the first, second and connecting gas passages and the open/close valves being formed in the planar component by micromachining; wherein the controller is configured to start each sample event by controlling one of the open/close valves from open to close when another of the open/close valves is closed and to stop the sample event by controlling the other of the open/close valves to open.

2. The gas chromatograph of claim 1, wherein the open/close valves are each configured to be electromechanically actuated.

3. The gas chromatograph of claim 1, wherein the open/close valves are each configured to be pneumatically actuated via pneumatic connections in the planar component.

4. The gas chromatograph of claim 1, wherein the open/close valves each have a valve body which is deflectable from a stable position at which a valve is open to a metastable position at which the valve is closed.

5. The gas chromatograph of claim 1, wherein all gas passages have the same inner diameter as that of the second separation column.

6. A modulator for sampling a chromatographic peak eluting from a first separation column into a second separation column of a comprehensive two-dimensional gas chromatograph, the modulator comprising a planar component including: a first gas passage having a first inlet end for connection of a carrier gas source and a first outlet end for connection of the second separation column; a second gas passage having a second inlet end for connection of the first separation column and a second outlet end; a connecting gas passage arranged between the first and second gas passages; two individually controllable open/close valves arranged in a parallel connection in the first gas passage between the first inlet end and a branch-off point of the connecting gas passage from the first gas passage, the first, second and connecting gas passages and valves being formed in the planar component by micromachining.

7. The modulator of claim 6, wherein the open/close valves are each configured to be electromechanically actuated.

8. The modulator of claim 7, wherein the open/close valves each have a valve body which is deflectable from a stable position at which a valve is open to a metastable position at which the valve is closed.

9. The modulator of any of claim 7, wherein all gas passages have the same inner diameter as that of the second separation column.

10. The modulator of claim 6, wherein the open/close valves are each configured to be pneumatically actuated via pneumatic connections in the planar component.

11. The modulator of claim 10, wherein the open/close valves each have a valve body which is deflectable from a stable position at which a valve is open to a metastable position at which the valve is closed.

12. The modulator of any of claim 10, wherein all gas passages have the same inner diameter as that of the second separation column.

13. The modulator of claim 6, wherein the open/close valves each have a valve body which is deflectable from a stable position at which a valve is open to a metastable position at which the valve is closed.

14. The modulator of any of claim 13, wherein all gas passages have the same inner diameter as that of the second separation column.

15. The modulator of any of claim 6, wherein all gas passages have the same inner diameter as that of the second separation column.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in greater detail by way of example and with reference to the drawing figures in which:

(2) FIG. 1 illustrates an exemplary block diagram of the gas chromatograph in accordance with an embodiment of the invention;

(3) FIG. 2 illustrates a view of a first embodiment of the modulator as a part of the gas chromatograph;

(4) FIG. 3 illustrates a view of a second embodiment of the modulator;

(5) FIG. 4 illustrates a block diagram and view of another exemplary embodiment of the modulator;

(6) FIG. 5 illustrates an exemplary embodiment of one of two open/close valves as a part of the modulator;

(7) FIG. 6 illustrates a first example for controlling the valves; and

(8) FIG. 7 illustrates a second example for controlling the valves.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(9) In the following description, like reference numerals designate like parts or elements.

(10) FIG. 1 illustrates a simplified block diagram of a comprehensive two-dimensional gas chromatograph, where only parts relevant to the embodiment of the present invention are illustrated.

(11) The gas chromatograph comprises a first separation column 1 through which a predetermined metered quantity of a gaseous sample 2 in the form of a short plug is fed via a carrier gas. The separation column 1 is configured to separate the sample components contained in the sample 2 as they flow through the column 1 so that the individual sample components arrive in succession at a detector 3 at the end of the column 1. For each detected component, the detector 3 supplies a detector signal in the form of a chromatographic peak, which is analyzed for quantitative determination of the component. The term peak is often, and also here, used for both the detector signal and the corresponding eluate emerging from the separation column 1. Unresolved peaks may overlap, partially or completely, compromising their identification and quantification.

(12) In order to separate and analyze each chromatographic peak or selected peaks for a second time by a second, such as fast-elution, separation column 4 and detector 5, a modulator 6 is positioned between the columns 1 and 4. The modulator 6 is based on valve operation and rapidly samples chromatographic peaks eluting from the first column 1 into the second column 4.

(13) The modulator 6 comprises a planar component 7 in which different gas passages are formed by micromachining, such as etching techniques. The gas passages consist of channels that have the same inner diameter as that of the second separation column 4. A first gas passage 8 has a first inlet end or port 9 to which a carrier gas source 10 is connected, and a first outlet end 11 to which the second separation column 4 is connected. A second gas passage 12 has a second inlet end 13 to which the first separation column 1 followed by the detector 3 is connected, and a second outlet end 14 that serves as a gas exhaust port. The first and second gas passages 8 and 12 communicate with each other via a connecting gas passage 15. The connecting gas passage 15 branches off, at an obtuse angle, from the portion of the second gas passage 12 that comes from the second inlet end 13. At this branch point, the second gas passage 12 continues at the same angle in another direction, so that the connecting gas passage 15 and the continuation of the second gas passage 12 form a symmetrical branching fork.

(14) Two individually controllable open/close valves 16, 17, which are formed in the planar component 7 by micromachining, are arranged in parallel connection in the first gas passage 8 between the first inlet port 9 and the branch-off of the connecting gas passage 15. In the illustrated example, the valves 16, 17 are configured to be pneumatically actuated via pneumatic connections 18, 19 in the planar component 7. The valves 16, 17 are controlled by a controller 20 via pneumatic lines 21, 22. The pneumatic controller 20 may include electromechanically actuated valves that are controlled in accordance with a control scheme 23 provided by a higher-level control system (not shown) of the gas chromatograph.

(15) FIG. 2 illustrates a view of the planar component 7 of the modulator 6. The planar component 7 comprises two plates 24, 25 that are positioned on top of one another and joined together. Congruent channels, which have respective semi-circular cross sections, are formed on those sides of the two plates 24, 25 that face one another. These channels form the gas passages 8, 12, 15 (FIG. 1) and the inlet and outlet ends 9, 11, 13, 14 at their lateral exit points from the plates 24, 25. At the inlet and outlet ends 9, 11, 13, 14, the cross sections of the gas passages 8, 12 may be enlarged to accommodate capillaries such as capillary 26 from the carrier gas source 10 or capillary 27 from the first column 1. This also applies accordingly to the pneumatic connections 18, 19 and pneumatic lines 21, 22.

(16) FIG. 3 illustrates another example of the planar component 7, where the valves 16, 17 are electromechanically actuated by solenoids or piezoelectric elements 28, 29 integrated in or mounted on the planar component 7 and controlled by the now electronic controller 20 (FIG. 1) via electric signal lines 21, 22.

(17) FIG. 4 illustrates on the left-hand side a block diagram and on the right-hand side a view of yet another embodiment of the planar component 7 that comprises different double plates 30, 31, 32, 33 assembled into a stack. The two outer double plates 30, 33 feature all fluidic ports or connections 9, 13, 11, 14, 18, 19 and electrical connections for the signal lines 21, 22 (FIG. 3) if the valves 16, 17 are electromechanically actuated. The double plate 32 contains the gas passages 8, 12, 15. The double plate 33 contains the valves 16, 17. As indicated by dashed lines 34, fluidic connection between the different double plates 30, 31, 32, 33 is established by vertical channels.

(18) FIG. 5 illustrates in a simplified form an example of the open/close valve 16 that is representative for both valves 16, 17. The valve 16 is formed in the planar component 7 by micromachining and has a valve body 35, here in the form of a membrane, which is deflectable from a stable position at which the valve 16 is open to a metastable position where the valve 16 is closed. The valve 16 is pneumatically actuated via the pneumatic connection 18 in the planar component 7.

(19) Referring again to FIG. 1, when one or both of the valves 16, 17 are open, carrier gas flows through the first gas passage 8 to the second separation column 4. A small percentage of the carrier gas 36 flows into the connecting gas passage 15 and prevents the eluate flowing in the second gas passage 12 from entering the connecting gas passage 15. When both valves 16, 17 are closed, the eluate is diverted from the second gas passage 12 into the connecting gas passage 15 and reaches the second separation column 4 via the first gas passage 8.

(20) FIGS. 6 and 7 illustrate two examples for controlling the valves 16, 17. The valves 16, 17 are controlled such that one valve, e. g., valve 16, initially switches from open to closed while the other valve 17 is closed, and after a predetermined time difference t the other valve 17 switches from closed to open. The time difference t defines the pulse width of the injection of the eluate from the second gas passage 12 into the connecting gas passage 15. In the example of FIG. 6, the switching status of each valve is maintained after each injection so that the responsibility for the start (or the end) of the injection pulse alternates between the valves 16, 17. In the example of FIG. 7, the switching status of each valve is changed at any time t.sub.0 between two successive injections so that the responsibility for the start or the end of the injection pulse remains with the respective valves 16, 17.

(21) The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive.

(22) Thus, while there have shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.