Integrated Microfluidic Helium Discharge Photoionization Detectors

Abstract Helium discharge photoionization detectors (HDPIDs) have been of increasing importance for detection of highly volatile compounds in gas chromatography (GC) and portable gas monitoring systems. The high ionization energy of these detectors (13.5–17.5 eV) allows for detection of virtually all compounds of interest, offering a distinct advantage compared to conventional PIDs, which can only detect compounds with ionization potentials below 10.6 (or 11.7, if using argon) eV. However, many current designs are bulky, power intensive, or helium intensive, restricting their usage to benchtop laboratory use. We recently developed a miniaturized HDPID that has low power and helium consumption, and small footprint. While offering suitable performance for portable GC applications, this design relies on hand assembly of silicon and Pyrex glass pieces, reducing fabrication yield, robustness, and repeatability. The current work improves on this prior device using an integrated, microfabricated μHDPID chip along with in-house designed plasma excitation and readout circuits. The μHDPID is characterized using permanent gases, light hydrocarbons, and formaldehyde, achieving low detection limits better than 10 pg, high linearity, rapid response time, short warm-up time, and high repeatability among devices. This integrated on-chip gas sensor offers advantages in ease of fabrication, yield and robustness, and repeatability. Therefore, it can be broadly used in portable GC for various applications.