Detector for Liquid Chromatography Based on Acoustic Emissions from an Oscillating Flame

Abstract

The acoustic flame detector (AFD) is examined as a novel detector for liquid chromatography (LC). It is based upon the acoustic emission frequency of an oscillating hydrogen/oxygen premixed flame and produces a universal response toward organic molecules. A stable frequency near 1000 Hz, which further depends on mobile-phase composition, is achieved for flow rates in the microliter per minute range. The mass flow sensitivity of the AFD demonstrates a linear response over 3 orders of magnitude and a detection limit (S/sigma = 3) of approximately 15 ng of C/s for a series of alcohols. For cyclopentanol, this amounts to an injected mass of approximately 77 ng based on a 0.5-microL injection of a 196 ppm solution in methanol (flow rate 20 microL/min methanol; peak width 30 s). Similar sensitivity is observed using a water mobile phase. Low-frequency (1/f ) noise contributions are dominant with or without mobile phase present. The AFD demonstrates a uniform molar sensitivity toward carbon compounds independent of their optical properties or volatility. Results suggest the device might serve as a simple, inexpensive universal LC detector.

gAn improved interface for universal acoustic flame detection in modified supercritical fluid chromatography

“…As a result, the acoustic flame detector (AFD) increases its pitch frequency as a function of the carbon content of the molecule. Thus, in this way the AFD has been found to provide a uniform response toward hydrocarbons that is qualitatively similar to an FID, but with a sensitivity and linear range that is typically at par with an ELSD [29,30].…”

“…Recently, we introduced a novel universal detector for use in LC and SFC that involves measuring the frequency of acoustic emissions from an oscillating hydrogen/oxygen flame [29,30]. The device is based upon the inner cone of the flame partially retreating downward into a capillary delivering a steady upward flow of premixed flame gases.…”

“…For instance, its simple and inexpensive design resembles an FID and can be readily adapted to a conventional FID detector base [29,30]. Most significantly however, unlike an FID, the AFD response toward analyte carbon content is not obscured by a modified SC-CO 2 mobile phase [30].…”

Acoustic methods of detection in gas chromatography

“…In subsequent work, Thurbide and Xia [65] reported that methane or helium, when used as the carrier gas, could yield the same GC-AFD sensitivity under different conditions. They then showed that the AFD could also be used i 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com in LC [65] and supercritical fluid chromatography [66] where an organic mobile phase was employed.…”

“…They then showed that the AFD could also be used i 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com in LC [65] and supercritical fluid chromatography [66] where an organic mobile phase was employed. Since the AFD can "null out" the background response toward carbon in the solvent (i. e., by adjusting the flame conditions), the detector can be used to detect carbon analytes within carbon-containing mobile phases.…”