ACOUSTIC FLAME DETECTOR FOR GAS-CHROMATOGRAPHY

A novel gas chromatography detector is described that uses acoustic si gnals from a partly premixed hydrogen-air name burning on top of a cap illary, The device, referred to as the acoustic flame detector (AFD), is based on the measurement of the frequency of acoustic transients ge nerated at the burner under a range of operating conditions, The prese nce of trace amounts of analyte in the flame was found to increase the frequency of these sonic bursts from the baseline level of similar to 100 Hz, The response of the AFD for n-dodecane, measured as the shift in frequency, was determined to be linear over similar to 3 orders of magnitude, with a minimum detectable level of about 1-5 ng C/s using the current system, The sensitivity correlates roughly with carbon con tent except for certain organometallics (Sn, Mn), which gave substanti ally enhanced signals, Some tailing was observed but became serious on ly for particular types of organometallics, The noise of the system wa s predominantly of the 1/f type, The effects of flow conditions, burne r geometry, and name gas constituents were investigated, The oscillati ons could be followed by acoustic, visual, electrical, and optical mea ns, The AFD mechanism is shown to involve oscillatory chemical kinetic s, in which the flame front (the inner cone) temporarily enters a few millimeters into the capillary during each cycle, thereby creating the acoustic signal.