Is Make-up Gas required for an FID if not being monitored?

Question

I'm looking for ways to reduce He consumption where not needed and we're currently running He into the FID as the make-up.

We currently run a Deans-switch system with the unwanted portion of our samples being sent to an FID.

We don't use the FID results in our analysis at all. The FID is only used to check the system/Deans Switch cut-points are correct (using concentrated stock solutions).

Do we need to run a make-up gas into it or can I just get by with H2 and Air?

Admin · Accepted Answer

This question has been marked as assumed answered.

garyb007 · Answer

Why don't you use nitrogen for the make-up gas.

mhardacker · Answer

Hello, Most detectors use a makeup gas to increase the flow rate through the detector body. This quickly flushes peaks out of the detector, avoiding component mixing and loss of resolution. it also optimizes the detector response and eliminate peak broadening (inside the FiD). Peak broadening will occur if there are dead volumes or large detector volumes in the system. This is especially important for capillary columns because the column flow rates are so small. The signal from mass flow responsive detectors, such as the FID, is not significantly affected by the makeup gas, while the sensitivity and signal to noise ratio are positively influenced by the makeup gas. Another advantage of makeup: it leads the combustion products (CO2/H2O), especially water, cleanly out of the FiD: it reduces the risk of corrosion! regards, M

shannon · Answer

Another option, If you are not using the detector, youc could just shut the detector down and disconnect the column so the gasses do not flow through the detector. If you needed to adjust your cuts or monitor your vent stream you would have to reconnect to the detector.

mhardacker · Answer

The probability of water precipitation is very low if the FID temperatures are high enough, but in times of 5890 the FID could not ignite well when water was present. In principle a FID can be operated without makeup gas, which manufacturers officially cannot approve ;-) In order to fill the detector volume better, an increase of the burner gas could be useful (45/450ml)

Is Make-up Gas required for an FID if not being monitored?

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