Design Miniaturized Detectors for Portable/Handheld Analytical Devices

     Increasingly, modern analytical chemistry is being formatted to take measurements in-situ rather than collecting field samples at a site of interest and transporting them back to a central laboratory for subsequent analysis.  In many instances these goals are supported by portable/handheld analytical devices which can be readily carried to remote locations for usage.  For example, some of the most interesting demonstrations of this are in the area of micro-analytical devices.  Such applications are of great interest to many sectors including chemical warfare gas detection, environmental emissions monitoring, and industrial process analyzers to name only a few.  While many exciting advances are being made in this area, there remains a continued need for the development of micro-detection methods that are suitable for this miniaturized format.  One such area of interest is in gas phase solute detection.

     Flame-based detection methods are conventionally some of the most widely explored and utilized techniques for measuring organic compounds in gaseous samples.  Not surprisingly then, there is a desire to transfer much of this acquired methodology into the new micro-analytical realm.  Two of the best examples of this are the Flame Ionization Detector (FID), which is universal for carbon compounds, and the Flame Photometric Detector (FPD), which is selective for sulfur, phosphorus, and other hetero-atomic containing organic compounds.  However, the main impediments to using flame-based detectors in portable devices are the large gas flows needed to support the flame (and hence which need to be carried along) and the inherent instability of conventional flames as their size is reduced in attempts to accommodate the micro-litre dimension channels within which a micro-analytical flame is required to operate.

     Our approach to this problem is the creation of a counter-current flame in-which the hydrogen and air flows oppose one another rather than streaming in the same direction in a concentric arrangement.  This results in a remarkably stable flame that burns 'upside down' in an opposing flow of gas.  As a result a micro-flame can be attained by this approach that has an extremely small size of about 30 nL, which can burn inside of a small enclosure.  Such an arrangement is well suited for adaptation to the channels of a micro-analytical device.  further, the flame is supported by only a few mL/min of gas flow, which also bodes well for portability.  To date the micro-FPD and micro-FID detectors that have been created based on this flame have provided performance that is on par with the well studied conventional FPD and FID.  Work continues in this area of studying the characteristics and applications of this novel method.  For instance, we have demonstrated that these flames can be successfully operated inside the end of a capillary gas chromatography column and provide 'on-column' FPD and FID detection.