388 Development of a Microvolume Membrane Sampling Probe for Detection of Ammonia

Friday, November 6, 2009: 8:40 AM
Charolais (Camino Real Hotel)
Hao Tang , Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX
Jon Thompson , Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX
Ammonia is present within earth's atmosphere at low ppb - ppm concentrations.  Ammonia is known to play an important role in atmospheric and biogeochemical processes. Monitoring the concentration of ammonia in the ambient air near agricultural operations is of particular interest due to the large source strength.  Indeed, domestic animals, agricultural crops, and fertilizers are believed to account for over 40 Tg of ammonia nitrogen emissions each year. 
We have explored use of 216 μm o.d. and 200 μm i.d. regenerated cellulose (RC) microdialysis tubes as sampling probes for ammonia.  The gas diffuses through the permeable probe into a stream of deionized water which continually perfused the tubing at 10 - 20 μL/ min.  The ammonium collected was analyzed through a fluorimetric method (OPA-sulfite) with LED excitation at 365 nm and measurement of fluorescence emission at 425 nm.  Since the sampling probe exhibits a very high surface area to volume ratio (approx. 200 cm2 / mL), the fiber acts as an efficient sampling device.  Aqueous concentrations of > 100 μM ammonium per ppm NH3 (g) have been observed.  In addition, the fluorogenic OPA-sulfite-ammonia reaction is very selective for ammonia over other amines that have been measured at low ppb levels in agricultural atmospheres.  This aspect of the derivatization chemistry allows online analysis of ammonia without need for separation prior to analysis.  The method has been applied to field measurements of ammonia at a swine barn facility with quantitative results agreeing with a reference method.
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