Embodiments of the present invention relate to ionization based-detection for micro analyzers. More specifically, the embodiments of the present invention relate to detector structures and detection methods for micro gas chromatographs (GC).
Micro analyzers, such as micro gas chromatographs, allow for a versatility and adaptability in detection techniques not found in conventional analyzers. Due to their small size and portability, micro analyzers can perform laboratory procedures on-site, in locations that significantly larger traditional instruments are unable to, providing practical detection results of numerous types of samples. Micro analyzers may be used in environmental or military applications, such as on vehicles or equipment, for example. Micro analyzers may also be utilized in processing as an in-line detection instrument or as a batch analyzer.
Micro analyzers, such as a micro gas chromatograph, have several limitations. Some types of detectors used in such an analyzer rely on radioactive sources, which are of environmental concern. In addition, some detectors utilized require a high start or “ignition” voltage that can cause noise and interference with electronics or other proximately located sensors. When trying to use multiple detectors in a single device, high energy input is of concern, as well as the possibility of differing pressure requirements for different types of detectors.
Embodiments of the present invention relate to a detector structure for use with or without a micro gas analyzer that is able to separate a sample gas mixture into its individual gas components. The detector structure comprises a photo-ionization detector (PID), an electron capture detector (ECD) and a vacuum ultra violet (VUV) source as an ionization source for both the PID and ECD. Further embodiments include a detector structure comprising two photo-ionization detectors (PID), two electron capture detectors (ECD), a vacuum ultra violet (VUV) source and the micro gas analyzer. The VUV source is an ionization source for both the inlet and outlet PIDs and ECDs, used in a differential detection mode, wherein the PIDs and ECDs utilize the same VUV source for ionization. The VUV may also provide ions for operation of microdischarge detectors (MDDs), ion trap mass spectrometers (ITMSs) and certain ion-based gas pumps.
References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
Embodiments of the present invention relate to a multidimensional detector structure by integration of detectors based on thermal conductivity (TC), photo-ionization (PI), ion-mobility (IM), electron capture (EC), and ion trap mass spectrometry (ITMS), for example. The detector structure may be used as a stand alone detector system in conjunction with any type of instrumental analysis device or as part of a micro analyzer, such as a micro gas chromatograph. The sample analyzed may be a liquid, gas or some combination of the two. The micro analyzer, such as a gas chromatograph, may heat the sample so that only gas contacts the detectors. A vacuum ultra violet (VUV) light is utilized as the photon and electron source by photo-ionization for one or more of the detectors integrated in the micro analyzer. The VUV light may also be used as the source for an ion drag pump used to mobilize the sample or analyte through the micro analyzer. The use of a VUV light replaces the need for environmentally sensitive radioactive sources or high temperature and energy thermionic emission sources. The utilization of a VUV light also simplifies the design and manufacture of the micro analyzer and the ignition voltage of detectors, such as a microdischarge detector (MMD), is also significantly reduced. The size of the VUV source (on the millimeter scale) may be large compared to the about 100-150-micrometer channels and about 10-100 micrometer detectors that are utilized in a micro analyzer.
Referring to
Referring to
The VUV energy source 21 is positioned adjacent to and can provide ions and electrons for such detectors as a PID 55 or MDD 53, for example. Other examples of detectors capable of utilizing the VUV energy source are electron capture detectors (ECD), ion/differential mass spectrometers (IMS/DMS), and ion trap mass spectrometers (ITMS). As shown in the figure, the TCD 57 and implicitly included chemical impedance detector (CID) are positioned outside the effective zone of the VUV energy source 21.
Referring to
The ECD 73 uses photo-electrons generated near the bottom of the sample channel 69 as they are knocked off the electrode 81, 83 metal and collected by the bottom set of interdigitated electrodes 75, 77. When an electron-attracting analyte flows by with a greater affinity for electrons than oxygen, it may capture such electrons and thus reduce the measurable ECD current. Metal film strips of negative polarity 77 are positioned on the bottom of the sample channel 69 and are in the path of the VUV photons emerging from between the PID electrodes 81, 83. The photo-electrons knocked out of the metal can normally be measured as a “null” current, which decreases when such electrons are “captured” (as mentioned above) by passing analyte molecules and dragged or carried away by the sample. Such decreases indicate an ECD signal about the presence, identity (by its microGC elution time) and concentration of an analyte.
In addition to the merged PID and ECD function, the micro analyzer may also include an ion trap mass spectrometer (ITMS). The ions to be trapped may preferentially be generated by the VUV source. Further, ions may be generated in close proximity to the ITMS by capturing photoelectrons from its own metal electrodes. Ions can also be provided by the VUV lamp for operation of MDD and IMS/DMS in addition to the merged PID and ECD.
A channel wafer 65 and heater wafer 63 provide structural support for the micro analyzer and its detectors. A material suitable for transmitting the energy from the VUV lamp 59 comprises the window 61, such as magnesium fluoride or lithium fluoride. A recess 67 optionally provides for a capillary attachment. A membrane 71 acts as a structural connects the heater wafer 63 and window 61. The membrane 71 may be comprised of SU-8 composite or polydimethylsiloxane (PDMS), for example.
For all figures shown, the VUV light may be positioned adjacent to the detector structure such that the detection signal is maximized before the VUV light is absorbed by air and the generated ions and electrons have recombined. The order of detectors may be of importance as the best analyte readings will come if the detectors are exposed to the most pristine analyte possible. Therefore, the non-ionizing, non-destructive detectors, such as a TCD and CID, are located in a parallel side-stream or upstream the sample channel from the location of the detectors requiring ions (and possible sample gas component fragmentation) for operation, such as a PID, ECD, IMS/DMS, ITMS and MDD. In one example of a possible configuration, the inlet stream could be split such that a series of one or more ionizing, or destructive, detectors are positioned in one branch and another series of one or more non-destructive detectors are positioned in another branch of the inlet. After passing through the non-destructive detectors, the sample would pass through the analyzer and then a second series of paired detectors near the sample exit. The sample passing through the inlet branch containing the destructive detectors would then be routed directly to the paired series of detectors positioned near the sample exit, without passing through the analyzer. In situations where the destroyed fraction of the sample is less than about 1%, it may not be necessary to separate the destructive and non-destructive detectors.
Referring to
The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.
This application claims priority to U.S. Provisional Application Ser. No. 60/681,776 (entitled MICRO FLUID ANALYZER, filed May 17, 2005) which is incorporated herein by reference.
This invention was made with Government support under Agency Contract Number FA8650-04-C-2502 awarded by the United States Department of AFRL Wight Lab. The Government has certain rights in this invention.
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