Chromatography Forum

have calibrated for four gases, H2, He, N2 and O2, none of the stds have the He and H2 together, the curves all come out nicely, but when our sample is injected, which has ~ 1.5% He, ~ 8% H2, ~10% O2 and balance N2, we get higher results than expected. (Total around 102%)
We are using a 100ul sample loop, injector temp of 125, column temp of 125, and 15 ft 1/8" SS molesieve 5A column.

any thoughts on why or how to solve. Trying to avoid multi gas stds with flammable range of H2 with O2.

Out of curiosity, are you using Argon carrier?

Which gases are measured higher than expected?

best wishes,

Rod

Yes, using argon as the carrier, and, usually, they all run high, but H2 and O2 most of the time.

Please detail how you are calibrating the each gas. Are you running pure stds and calling that area 100%?

If you do so you would have to demonstrate that the detection curve is linear, has this been done?

Obviously, if the detection response curve is not linear then your values could all be off at lower concentrations and this could be the reason you are not finding the partial components to total to 100% but are totaling higher amounts.

A possible solution is to use two calibration standards.

You could prepare a std at 2% Helium 10% Hydrogen and 88% Nitrogen and calibrate those gases at levels you expect to measure. Then with a separate std calibrate Oxygen with a 10% Oxygen 10% Helium and 80% Nitrogen composition.

This way you would not be using standards with composition you might find hazardous.

best wishes,

Rod