A photoacoustic (PA) spectrometer with H-type first longitudinal resonant cells for ammonia detection is developed. A new PA cell structure is designed to accelerate the drift velocity of the sample gas near the cell surface, so that the short response time at the flow rate of 100 sccm (standard cubic centimeter per minute) is achieved. The response time of 5 min and detection limit of 0.86 ppbv is reached for ammonia concentration measurement with a Teflon polytetrafluoroethylene (PTFE) cell. Further improvement could be expected when using a brass cell with a high quality Teflon fluorinated ethylene propylene (FEP) coating.
© 2007 Chinese Optics LettersPDF Article