Microfabricated Nitrogen-Phosphorus Detector: Chemically Mediated Thermionic Emission

Many chemical warfare agents and toxic industrial chemicals contain nitrogen and phosphorus atoms. Commercially available benchtop Nitrogen-Phosphorus Detectors (NPDs) for gas chromatographs are highly selective for nitrogen and phosphorus compared to carbon. However, the detection mechanism for these thermionic detectors is poorly understood despite 60 years of use. In addition these detectors require the use of flammable gas and operate at high power. We developed a microfabricated NPD (μNPD) with similar selectivity that does not require the use of flammable gas and uses relatively low power. Our μNPD consists of an alkali metal silicate thin film spray coated onto a microhotplate. The silicate thin film is responsible for providing the thermionic emission necessary for analyte detection. We conducted a series of experiments designed to better elucidate the detection mechanism. Our results indicate that surface catalyzed ionization of nitrogen and phosphorus containing analytes is the most likely mechanism.

[1]  Tong-Ho Kim,et al.  Surface oxide relationships to band bending in GaN , 2006 .

[2]  P. Patterson.  A specific detector for nitrogen and halogen compounds in TLC on coated quartz rods , 1985, Lipids.

[3]  Maciej Gutowski,et al.  Accurate valence band maximum determination for SrTiO3(001) , 2004 .

[4]  H. Carlsson,et al.  Response mechanisms of thermionic detectors with enhanced nitrogen selectivity. , 2001, Analytical chemistry.

[5]  P. Schofield,et al.  Probing the response mechanism of the thermionic detector by resonance enhanced ionization spectroscopy , 1998 .

[6]  E. P. Hunter,et al.  Evaluated Gas Phase Basicities and Proton Affinities of Molecules: An Update , 1998 .

[7]  B. H. Zwerver,et al.  Spectroscopic investigation of the mechanisms of the alkali bead detector for gas chromatography , 1988 .

[8]  P. Patterson.  A comparison of different methods of ionizing GC effluents , 1986 .

[9]  P. Patterson.  Recent Advances in Thermionic Ionization Detection for Gas Chromatography , 1986 .

[10]  Joel F. Liebman,et al.  Evaluated Gas Phase Basicities and Proton Affinities of Molecules; Heats of Formation of Protonated Molecules , 1984 .

[11]  P. Patterson.  New uses of thermionic ionization detectors in gas chromatography , 1982 .

[12]  P. Patterson,et al.  An Improved Thermionic Ionization Detector for Gas Chromatography , 1982 .

[13]  Z. Vajta,et al.  On the Mechanism of Kolb's N-P Selective Detector , 1979 .

[14]  P. Patterson.  Selective responses of a flameless thermionic detector , 1978 .

[15]  P. Patterson,et al.  Thermionic Nitrogen-Phosphorus Detection with an Alkali-Ceramic Bead , 1978 .

[16]  B. Kolb,et al.  Reaction Mechanism in an lonization Detector with Tunable Selectivity for Carbon, Nitrogen and Phosphorus , 1977 .

[17]  A. Karmen,et al.  Enhancement of the Response of the Hydrogen Flame Ionization Detector to Compounds containing Halogens and Phosphorus , 1964, Nature.