Development of a Micro-flame Ionization Detector for Portable Gas Chromatography

A micro-flame ionization detector (mu-FID) was developed. Differing from the traditional FID, air was introduced from the side of the upper part of the mu-FID body, flowing downwards into the burning chamber along a narrow round gap between the collection electrode and the inner wall of the detector body. When the coaxial flow of air reached the bottom of the chamber, it turned 180 degrees and flowed out through the hollow collector. The jet tip was located along the axis of the chamber and the collector, where the air flow was extremely stable, yielding extremely low noise level. A much higher polarization voltage was then applied to enhance ionization efficiency. Several important parameters were optimized, including the material and inner diameter of the jet tip, the length of collector, the distance between jet tip and collector, polarization voltage and gas flow rate. Under the optimized condition, the signal-to-noise ratios improved over one order of magnitude when polarization voltage increased from 150 V to 800 V. The limit of detection of the mu-FID was 1 x 10(-12) g/s, with a linear response of five orders of magnitude. Compared with traditional FID, the mu-FID only needs two kinds of gases (hydrogen and air) and gas consumption decreases 70%. The detector is small in volume, simple in structure, sensitive and easy to construct, suggesting that it is an excellent detector for portable GC. The mu-FID was also applied to analyze five phenolic compounds in real water samples.