A planar micro-flame ionization detector with an integrated guard electrode

Abstract

The flame ionization detector (FID) quantifies small concentrations of organic compounds by flame ionization of hydrocarbons and measurement of the resulting ion current. The ion current represents the number of carbon atoms in the sample gas. The miniaturization of the FID by MEMS technology (µFID) is expected to increase its use, because of reduced oxyhydrogen consumption. This loosens safety precautions and makes portable applications possible. In contrast to a former µFID design, the current planar µFID is designed to prevent environmental air from entering the system and deteriorating the measurement signal. The oxyhydrogen flame burns in the silicon plane of an almost completely encapsulating glass-silicon-glass sandwich. Only a small opening remains for removal of the exhaust gas from the system. In between the detector electrodes, a guard electrode is integrated to intercept and by-pass leak currents past the picoammeter, which then only measures the ion current. Due to the design of the guard electrode, small leak currents are still measured by the picoammeter. Yet, these leak currents can be corrected for to obtain the ion current. Measurements of the ion current as a function of the applied voltage and the sample gas flow show expected FID behaviour.

Characterization of a microelectromechanical systems-based counter-current flame ionization detector

“…Orthogonal dimensions of the micro-burner, including wafer thickness (500 m), the nozzle height (100 m) and the depth of the cavity in the top glass substrate (300 m), are based on preliminary results [4,5]. The outlet width measures 700 m. Other in plane dimensions, such as the width of the nozzles w and the distance between the nozzles d ( Fig.…”

“…This leakage current may be many times larger than the ion current to be measured. Yet, this leakage current can be intercepted by a guard electrode [4]. This guard electrode is realized as a sputtered chromium thin film underneath the measurement electrode and an electrically isolating sputtered silicon oxide layer (Fig.…”

“…The research within our group [2][3][4][5][6][7] and of a few other [8][9][10][11][12][13] focuses on the miniaturization of the FID to reduce gas consumption for mobile applications. This work reports on the characterization of the latest and most successful version of a MEMS-based FID (FID), in which the flame burns in the silicon plane of a glass-silicon-glass sandwich.…”

“…This work reports on the characterization of the latest and most successful version of a MEMS-based FID (FID), in which the flame burns in the silicon plane of a glass-silicon-glass sandwich. In contrast to previous designs with a single-nozzle micro-burner for premixed hydroxygen flames [4,5], the current FID is inspired by the work of Hayward and Thurbide [10][11][12][13] and consists of an opposed-nozzle micro-burner for extremely stable counter-current diffusion flames (cc-FID) [6,7]. Hydrogen and oxygen are supplied from opposite directions and react in the vicinity of a so-called stagnation point, where gas flow velocities are small.…”

Fast pyrolysis kinetics of expanded polystyrene foam

“…The raw peak intensity (ion current) detected by the FID at any instant is proportional to the number of carbon atoms present in the volatiles, 4 and the area under the curve between zero and time ''t'' is proportional to the cumulative amount of the volatiles generated by the pyrolysis reaction. By forming the ratio of the instantaneous value to the total area under the curve, the experimental reaction yield Y(t) exp was computed…”