Development and application of a milli-whistle for use in gas chromatography detection

A simple milli-whistle was developed for the use in GC (gas chromatography) detection, in which, compared to a thermal conductivity detector (TCD), 1 order of magnitude superior sensitivity can be obtained. The milli-whistle can be connected to the outlet of a GC capillary. The gas and makeup gas passing through the capillary produces a sound as it passes through the milli-whistle (i.e., the gas of the GC eluate). The sound can easily be detected by a microphone, which, after a Fourier transform (FT) by means of a LabVIEW (Laboratory Virtual Instrumentation Engineering Workbench) built-in program, a very sharp frequency peak (full width at half-maximum, ∼1.6 Hz) can be simultaneously observed. As a result, GC elutes can be qualitatively determined on the basis of their retention times, and a quantitative analysis can be achieved on the basis of the frequency shifts. When the makeup and carrier gases used were nitrogen, in the case of gas samples, including hydrogen, helium, argon, and carbon dioxide, the limits of detection were found to be ∼3 μL/each injection; in the case of liquid samples, including methanol, cyclohexane, tetrahydrofuran, hexane, and acetone, the limits of detection were determined to be ∼10 μg/each injection, respectively. When the gases were changed to hydrogen, the limits of detection were dramatically improved. When acetone was selected as the model sample, a linear relationship was found in the range of 0.2-200 μg/injection.