A Compact Ammonia Detector with Sub-ppb Accuracy Using Near-Infrared Photoacoustic Spectroscopy and Preconcentration Sampling

Abstract

This paper describes the first successful application of a preconcentration unitto increase the sensitivity of a photoacoustic ammonia concentration measuring instrument. A diode laser based near-infrared (1532 nm) photoacoustic ammonia monitoring instrument was combined with a tungsten (VI) oxide coated preconcentration unit to reach a sub-ppb detection limit with a compact, automatic measuring instrument. The system has no measurable cross-sensitivity to common atmospheric gases, most importantly to water vapor and carbon dioxide. The minimum detectable amount of ammonia is 2.9 ng, which means a minimum detectable concentration of 0.5 ppb with a 30-min measurementtime. Results of intercomparison measurements carried out both under laboratory and field conditions with reference to an electrochemical AMANDA instrument prove the applicability of the system in environmental ammonia concentration monitoring.