49
GCDetectors
HID -Helium IonizationDetector
Arc
electrode
Collector
electrode
Arc electrode
Arc
window
Make-up
gas
Sample-laden
carrier from
column
SRI HID
Detector
• Universal (except neon)
• Detect from1-2%down to 10ppm
• Requiresonlyheliumcarrier andmake-upgas
• Perfect Complement to theTCD!
TheHelium IonizationDetector is a “universal” detector which responds to all molecules except neon. The
HID is particularly useful for volatile inorganics likeNOx, CO, CO
2
, O
2
, N
2
andH
2
which do not respond on
the FID or other detectors. Unlike an FID, the HID needs no hydrogen or air. The HID requires only helium
carrier and make-up gas, and delivers sensitivity in the low ppm range. Many labs are reluctant to store
hydrogen fuel gas for safety reasons, so the fact that theHID requiresonlyhelium isasigniicant advantage.
TheHID is especially useful in combinationwith a Thermal ConductivityDetector. The TCD is not sensitive
enough to detect low ppm concentrations, while the HID saturates in the low percent range. When using
bothdetectors in series, it is possible to cover 10ppm to 100%.
Unlike other HID designs, the SRI HID can be
heated to 350°C and can easily be disassembled
for cleaning. The HID incorporates robust, easily
serviceable electrodeswhich support a low current
arc through the helium make-up gas low. This
elevates the surrounding 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, ampliied,
and output to the data system. Our HID features
a window through which the low current arc is
visible, so it iseasy for theoperator toverify that the
detector is functioning.
Thischromatogramshows theseparation
of a 100ppmBTEXPlus sample.
8690-0030
HIDdetector
