WO1999040422A1

WO1999040422A1 - A valveless gas chromatographic system with pulsed injection and temperature programmed elution

Info

Publication number: WO1999040422A1
Application number: PCT/US1999/002777
Authority: WO
Inventors: Lawrence V. Haley; Govindanunny Thekkadath
Original assignee: Haley Lawrence V; Govindanunny Thekkadath
Priority date: 1998-02-10
Filing date: 1999-02-10
Publication date: 1999-08-12
Also published as: EP1062504A1; AU2665999A; EP1062504A4; JP2002502970A; CA2320445A1; CN1296565A

Abstract

A portable gas chromatograph includes a sample adsorbing ribbon (220) having a sampling position (205) and second desorbing position (206). The sample is desorbed by activating heaters (210, 211). The desorbed sample passes to a chromatography column (209b) which is then heated by a third heater (212). The separated sample is passed to a detector (213) for analysis.

Description

A VALVELESS GAS CHROMATOGRAPHIC SYSTEM WITH PULSED INJECTION AND TEMPERATURE PROGRAMMED ELUTION

CROSS-REFERENCE TO RELATED APPLICATIONS

The following patent application is based on and claims the benefit of U.S. Provisional Patent Application Serial No. 60/074,195 filed February 10, 1998.

DESCRIPTION Field of the Invention

The present invention relates generally to detection and analysis of gaseous components and more particularly to a valveless system using gas chromatography with pulsed injection and temperature programmed elution.

Background of the Invention

Gas chromatography is an established analytical technique for separating the components of a gaseous mixture as the mixture flows through a tubular column. There are many different ways of injecting the initial sample into the column and performing the separation. For example, one known method of carrying out the separation in open tubular columns is shown in Figures la and lb. In this method, valve 1 admits a small volume of the sample flowing through the loop 2 into the column 3 when the valve is switched from the sampling position shown in Figure la to the injection position shown in Figure lb. This volume of sample is then carried down the column by a flow of carrier gas through the port 4 and 5 of the valve and separated into its components when it interacts with the column wall coated with the appropriate separating medium. The net result is that the components exit the column as separate volumes at different times. The time between the injection and the exit of a component is called its retention time. The components are detected by an appropriate detection system, for example, an electron capture detector (ECD) or a thermal conductivity detector. The signal generated by the detector (the chromatogram) can then be plotted out for analysis.

The speed at which analysis takes place in this system is dependent on several factors including the type and length of the column, its temperature and the velocity of the carrier gas in the column. In general total analysis times are in the order of minutes to hours. Sample preparation and injection can take several minutes to hours depending on the nature of the sample. Thus for real time analysis this process needs to be speeded up considerably.

Real time analysis is highly desirable when using the technique of gas chromatography for quickly detecting and identifying compounds contained in narcotics and explosives. Then sampling and detection systems based on gas chromatography can be used for checking suspicious objects which could contain explosive devices or controlled drugs and narcotics. Such devices are useful at border crossings and airports for identifying and preventing drug smuggling or terrorist activity.

Therefore, it is also highly desirable to make such detection system portable and operable in real time.

-2- Moreover, it is also desirable to make such systems battery operable. Gas chromatography of drug or explosive samples require that the sampling separation systems work at high temperatures typically in the region of 100 to 300 degrees Celsius. Presently, there are no energy efficient or portable GC-IMS devices which can operate in the high temperature regime for analyzing drugs or explosives because power requirements for gas chromatography systems usually preclude battery operated portable systems of practical size and weight.

Therefore, it is also highly desirable to have a gas chromatography system with minimum power consumption without sacrificing performance.

Summary of the Invention

The present invention provides a novel design and method of operation for a pulsed high speed sampling and gas chromatographic (GC) separation system which is capable of sampling and analyzing particles and vapors containing drug and explosive residues in less than twenty seconds and which at the same time consume very little power. The speed and power savings provided by the present invention uses a heat-on-demand (HOD) technology explained below.

There are several important advantages for using the pulsed analysis technique in simple, portable, low power GC-IMS sample gathering and analytical system as disclosed by the present invention. Because of the pulsed nature of the system, power consumption takes place only when the system is analyzing, greatly increasing the overall energy efficiency of the system

-3- compared to static systems where the components are always maintained at high operating temperatures . This makes its use practical in hand-held analytical devices using batteries as power sources. Moreover, the pulsed heating sequence avoids the use of valves to switch a sample packet into the column as is done in static high temperature systems, making the system simpler and more reliable.

Advantageously, the system of the present invention may operate as one integrated system for sample gathering, analysis, and data presentation, thus, making it an ideal portable real-time analytical instrument for many applications, including drug and explosive checks and searches at border points, airports, etc., and also for air quality monitoring.

Furthermore, the present invention may be used with an ion mobility spectrometer (IMS) device as a second analyzer. Using the IMS greatly increases the overall selectivity and sensitivity of the instrument without adversely affecting its performance or energy efficiency. Further features and advantages of the present invention as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements .

Brief Description of the Drawings

Preferred embodiments of the present invention will now be described, by way of example only, with reference

-4- to the accompanying drawings in which:

Figures la and lb illustrate an example of separating the components of a gaseous mixture as the mixture flows through a tubular column as known in the prior art systems;

Figure 2a illustrates a schematic diagram of the valveless gas chromatographic system of the present invention; and

Figure 2b illustrates a graphical representation of the heating and cooling sequence of the present invention.

Detailed Description of the Preferred Embodiment of the Invention

In the preferred embodiment, the valveless gas chromatographic system of the present invention is an integrated sampling and analysis device. Such integration with an analysis device makes it possible to use the system as a portable, hand-held device. A description of the hand-held device which integrates the system of the present invention can be found in the related and commonly owned PCT Application No. PCT/US98/22092 entitled A SAMPLE TRAPPING ION MOBILITY SPECTROMETER FOR PORTABLE MOLECULAR DETECTION, filed on

October 20, 1998, the description of which is fully incorporated herein by reference thereto.

Figure 2a shows a schematic diagram of the system of the present invention. The system may be divided into a sampling section and analysis section. The system includes a sample trap having a ribbon about half an inch wide wound on bobbins 201 and 202 and passing between the

-5- sampling and analysis sections. The material used to make the ribbon may be a metallic mesh typically of size 400 or more or other porous type which allows air to pass through freely but traps small particles and vapors. The vapor trapping or collecting ability may be increased by coating the ribbon with an absorbing media known in the art for use in absorbing the desired molecules of interest .

A nozzle 203 and a pump tube 204 are cylindrical entities with soft 0 ring seals at the ends that are closer to the ribbon. When the machine is in the sampling mode, 203 and 204 form a tight seal on portion 205 of the ribbon. A vacuum pump attached to the pump tube 204 sucks vapors and/or particles through the sampling nozzle 203 onto the sampling area 205 of the ribbon. After a predetermined time duration of sampling, e.g., few seconds of sampling, the nozzle 203 and the pump tube 204 are moved away from the ribbon to break the seal. The moving process is accomplished with the aid of electric motors controlled by a computer 410. After the seal is broken, the ribbon is moved in the direction shown by the arrow 220 to the location at 206. The movement of the ribbon is also accomplished with the aid of electric motors and position sensors which stop the motors after positioning the sample.

Once at position 206, the desorption port 207 and the injection port 208 move towards the ribbon under motor control and form an air-tight seal around 206. The desorption port 207 is a cylindrical entity less than 1/4" in diameter, and may include a built-in electric heater 210 to heat the gas passing through the ribbon to a temperature of 200 Celsius or more within a few

-6- seconds. A carrier gas flows into 207 and gets heated by the heaters so that when the hot gas exits out of the desorption port 207 and impinges on portion 206 of the ribbon, it in turn heats the sample trapped in the ribbon at 206. The rate of flow of the carrier gas is typically about 50 to 200 cc/min.

At the time the desorption port 207 is hot, the injection port 208 is also heated to the same temperature using the same technique as for the desorption port 207 with the aid of electric heater 211. The injection port 208 has a more complex construction because it has the gas chromatographic column 209 attached in a unique manner. The column 209 in the preferred embodiment has a metallic jacket which is directly heated by passing a current through it from a controlled source 212. Portion 209a of the column 209 is inside the injection port 208 and portion 209b is outside the injection port 208. The far end of 209b is connected to the detector 213. This detector 213 is preferably an IMS detector. The carrier gas flowing into the injection port 208 goes directly into portion 209a of the column and thence into portion 209b. When the desorption port 207 and the injection port 208 are heated, the column 209 is not heated. This causes the vapors of the trapped sample at 206 which are released by the hot carrier gas to move through portion 209a of the column and condense at the beginning of portion 209b of the column.

Once the sample has settled down in the front end of the column 209, the heaters 210 and 211 are switched off, typically by a computer controller 410. The temperatures of the heaters rapidly drop to ambient in a few seconds because the ports 207, 208 are constructed with the

-7- minimum amount of heat capacity. The computer 410 senses the temperature of the ports 207, 208 and when they have reached an appropriate minimum value which is preferably about 20 degrees Celsius above the ambient, the computer 410 turns on the heater 212. This causes the column portions 209a, 209b to heat up rapidly from ambient to more than 200 degrees Celsius in a few seconds. The rate of this heating is controlled by the computer program. Since there is a carrier gas flow in the column during the heating cycle, the condensed compounds move down the column and separate into the individual components and exit into the IMS 213 at different times. The IMS ionizes these packets of individual components in the sample and further separate the components according to their mobility in the drift gas flowing in the IMS. The individual ion packets are then collected on an electrode and amplified electronically by amplifier 214 for further signal processing and display 215 using the computer 410. It should be noted that detection devices other than IMS may be used, e.g., by attaching a different detection device at the end of the column 209.

The sequence of heating and cooling of the analysis system is critical to the success of the device as a programmed pulsed gas chromatographic system. A graphical representation of the heating and cooling sequence is shown in Figure 2b where the horizontal axis is the time axis common to the three graphs. The three separate vertical axes are the temperature axes. The maximum values of the temperatures depend on the nature of the compounds being analyzed, and are typically around 200 degrees Celsius for explosive and drug compounds. The rate of rise and fall of the temperature programming of the column is in general constant, but can be changed to follow a desired curve using the computer 410 to control the duty cycle of the heater. As shown in Figure 2b, there is no delay between the heating cycles 240, 250 of the heaters in the ports 207, 208, but the column heating starts as shown at 260 after these heaters have cooled down, to achieve the desired effect described above .

In addition, the heated portions have low heat capacities and are designed to dissipate the heat efficiently. Such a design is important for achieving fast analysis times. With the system of the present invention as described above, the ports 207, 208 and the column 109 can be heated and cooled over the working range in a few seconds.

While the invention has been particularly shown and described with respect to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

CLAIMSWe claim:

1. A high speed sampling and gas chromatographic separation system which is capable of sampling and analyzing molecules of interest, the system comprising: an input device for collecting sample particles having the molecules of interest at a first position; a port device capable of being heated by a heat pulse, the port device connected to the input device to receive the sample particles having the molecules of interest at a second position, the molecules of interest releasing a vapor in response to the heat pulse applied to the port device; and a gas column device connected to the port device, the gas column device receiving the vapor, the gas column device having a temperature lower than the port device, wherein the vapor is condensed in the gas column device, the gas column device further capable of being heated by a heat pulse, wherein in response to the heat pulse applied to the gas column, the condensed vapor of the molecules of interest separate into individual components and exit the gas column at different times.

2. The system as claimed in claim 1, wherein the system further includes: a detector connected to the gas column, the detector receiving the individual components of the condensed vapor, the detector for analyzing the molecules of interest.

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3. The system as claimed in claim 1, wherein the port device includes : a desorption port for receiving a carrier gas, the desorption port capable of being heated by a heat pulse and further heating the carrier gas in response to the heat pulse; and an injection port positioned to receive the carrier gas from the desorption port, the injection port capable of being heated by a heat pulse, wherein the molecules of interest is positioned between the desorption port and the injection port, the sample particles having the molecules of interest being heated as the heated carrier gas exits the desorption port and enters the injection port, the heated carrier gas further causing the molecules of interest to release a vapor into the injection port.

4. The system as claimed in claim 3, wherein the gas column device has a first portion and a second portion, the first portion positioned inside the injection port, the second portion positioned outside the injection port, wherein the carrier gas carrying the vapor of the molecules of interest is transported from the first portion to the second portion.

5. The system as claimed in claim 4, wherein the system further includes: a detector connected to the second portion, the detector receiving and ionizing the vapor of the molecules of interest into ionized components for analysis .

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6. The system as claimed in claim 5, wherein the system further includes: an amplifier connected to the detector for amplifying signals generated by the ionized components for further signal processing.

7. The system as claimed in claim 6, wherein the system further includes an output device for presenting the signals processed to a user.

8. The system as claimed in claim 1, wherein the gas column further includes a metallic jacket capable OJ. being directly heated by passing a current through the metallic jacket.

9. The system as claimed in claim 3, wherein the system further includes a first heater capable of transmitting pulsed heat to the desorption port.

10. The system as claimed in claim 3, wherein the system further includes a second heater capable of transmitting pulsed heat to the injection port.

11. The system as claimed in claim 3, wherein the system further includes a third heater capable of transmitting pulsed heat to the gas column.

12. The system as claimed in claim 3, wherein the system further includes: a nozzle for inputting the sample particles having the molecules of interest to be collected and

-12- vaporized for detection, the nozzle having a first end where the sample having the molecules of interest are inputted, the nozzle further having a second end; a pump tube attachable to the second end of the nozzle; and a ribbon passing between the nozzle and the pump tube, the ribbon for collecting the sample particles having the molecules of interest at the first position, wherein the sample particles having the molecules of interest are sucked through the nozzle onto the ribbon by the pump tube, the ribbon having the sample particles having the molecules of interest further moved along to be positioned between the desorption port and the injection port at the second position.

13. The system as claimed in claim 12, wherein the ribbon is a porous type.

14. The system as claimed in claim 12, wherein the ribbon is a metallic mesh.

15. A method for high speed sampling and analysis of molecular components in a gas chromatographic separation system, the method comprising: receiving sample particles having molecules of interest at a port device; heating the port device with a heat pulse to a selected temperature to transform the molecules of interest into a vapor; moving the vapor to a gas column device having a temperature less than the port device; condensing the vapor in the gas column device;

-13- and heating the gas column device with a heat pulse to a predetermined temperature to cause the vapor to separate into individual components and exit the gas column at different times.

16. The method as claimed in claim 15, wherein the method further includes : receiving the individual components into a detector device when the individual components exit the gas column device.

17. The method as claimed in claim 15, wherein the method further includes : collecting the sample particles having the molecules of interest onto a ribbon from an input nozzle before the step of receiving.

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