The Helium Ionization Detector is a "universal" detector which responds to all molecules except neon. The HID is particularly useful for volatile inorganics like NOx, CO, CO₂, O₂, N₂ and H₂ which do not respond on the FID or other detectors. Unlike an FID, the HID needs no hydrogen or air. Requiring only helium carier and make-up gas, the HID delivers sensitivity in the low ppm range. For labs that are reluctant to store hydrogen fuel gas for safety reasons, the helium-only HID is a significant advantage.

The HID is especially useful in combination with a TCD detector. The TCD is not sensitive enough to detect low ppm concentrations, while the HID saturates in the low percent range. When using both detectors in series, it is possible to cover 10ppm to 100%.

Unlike other HID designs, the SRI HID can be easily disassembled for cleaning. The HID incorporates robust, easily servicable electrodes which support a low current arc through the helium make-up gas flow. This elevates the helium to a metastable state. When the metastable helium molecules collide with sample molecules as they elute from the column, the sample molecules are ionized and attracted to a collector electrode, amplified and output to the data system. Our HID features a window through which the low current arc is visible, so it is easy for the operator to verify that the detector is functioning.