Method and apparatus for determining concentration of NH-containing species

Abstract

A method and apparatus for determining ammoniacal species concentration in a gas sample. In one embodiment, trace concentration of ammonia in an air sample is determined by monitoring emission intensity from an excited radical species (NH*), which is produced in a reaction between ammonia and fluorine. The observed emission intensity is compared with calibration data obtained from previously analyzed gas samples containing ammonia. The method and apparatus can also be adapted to detect ammoniacal species concentration in other NH-containing gas samples.

What is claimed is:  
     
         1 . An apparatus for determining concentration of an ammoniacal species in a first gas sample, the apparatus comprising: 
 a reactor having a first inlet for introducing said first gas sample into a reaction zone inside said reactor;    an optical detection-system to detect radiation arising from said first gas sample inside said reactor;    a second inlet for introducing a second gas sample containing fluorine into said reactor, wherein said radiation arising from said first gas sample is generated from a reaction between said first gas sample and said second gas sample within the reaction zone inside said reactor; and    a data acquisition and storage system to convert said detected radiation into a radiation intensity parameter, wherein said radiation intensity parameter is used to determine concentration of said ammoniacal species in said first gas sample.    
     
     
         2 . The apparatus of  claim 1 , wherein said reactor further comprises a pressure measuring device, first and second gas flow controllers to control said first and second gas sample flows into said reactor and a vacuum pump, wherein said pressure measuring device, said first and second gas flow controllers and said vacuum pump cooperate with each other to maximize said radiation generated from said reaction between said first and second gas samples.  
     
     
         3 . The apparatus of  claim 2 , wherein a reaction between said first and second gas samples is performed in a pressure range of about 0.1 to about 50 mbar.  
     
     
         4 . The apparatus of  claim 2 , wherein said optical detection system comprises an optical device which selectively transmits radiation originating from said reaction between said first and second gas samples and a photodetector capable of detecting said transmitted radiation.  
     
     
         5 . The apparatus of  claim 4 , wherein said optical device transmits radiation with a full-width half-maximum bandpass of between about 331 nm and about 341 nm.  
     
     
         6 . The apparatus of  claim 1 , wherein said first gas sample comprises ammonia.  
     
     
         7 . The apparatus of  claim 5 , wherein said radiation arising from said first gas sample originates from NH* radical.  
     
     
         8 . The apparatus of  claim 6 , wherein said concentration of ammonia in said first gas sample is determined by comparing said radiation intensity parameter with at least one provided set of calibration data regarding ammoniacal species concentration or a functional relationship correlating detected radiation from excited imidogen radicals with ammoniacal species concentration.  
     
     
         9 . The apparatus of  claim 8 , wherein said calibration procedure is performed inside said reactor by reacting each one of a plurality of calibration gas samples comprising known concentrations of ammonia with a reactant gas comprising fluorine, detecting radiation from NH* radicals generated from each reaction, converting said detected radiation into a calibrated radiation intensity parameter for each of said plurality of calibration gas samples, and forming calibration data associating said calibrated radiation intensity parameter with its corresponding said known concentration of ammonia.