Characterization of a modular microfluidic photoionization detector

Photoionization detectors with a small ionization chamber can contribute to overall gas analyser miniaturization. This work reports the characterization of a microfluidic photoionization detector prototype (μPID) which is constructed to be modular for easy replacement of the components and maintenance. The device is fabricated by micromilling and electrical discharge machining, dispensing clean room fabrication techniques. The μPID ionization chamber is a microchannel and four channel designs are presented and tested in experiments in order to evaluate the influence of the geometrical parameters on the detector performance. The chamber volumes of the channel designs range from 1.1 to 6.7 μL. Experimental characterization of the prototype is performed when it is used without and with a portable gas chromatograph (GC) for volatile organic compounds (VOCs) analysis. When a sample of 100 ppm toluene is injected directly into the μPID, it can generate a current signal up to ∼4 nA. When used without a GC, the device showed a linear response for an injection of toluene gas concentrations ranging from 1 to 100 ppm. A combination of high illumination area and electrode area resulted in the highest signal in the μPID with a detection limit of ∼40 ppb of toluene. When integrated to the portable GC, the detection limit reached for toluene is ∼140 ppb. The detection limit for toluene was further reduced to low ppb levels (∼5 ppb) when a preconcentrator was integrated into the sampling loop of the portable GC.