Anybody have experience using hydrogen generators to provide hydrogen for both carrier gas and fuel for FID detectors? What about with larger capacity models to supply hydrogen to multiple GCs?
By John Hinshaw on Thursday, July 15, 1999 - 11:50 am:
Hydrogen generators are well suited to supplying FID combustion gases. However, if the intent is to supply carrier gas several additional considerations are important.
First, make sure that the generator is a relatively new one, less than a few years old. There have been some technological advances recently; whereas some of the manufacturers were hesitant in the past to discuss or support carrier-gas applications, I spoke with several at this year's PittCon who were encouraging.
Second, select one with at least twice the rated capacity as you may now require; this allows room for growth while permitting the most stable possible gas outlet pressure.
Third, be sure to use additional filtering outside the gas generator for the carrier-gas lines (separately from the FID lines). The gas generators do a good job of removing hydrocarbons, oxygen, and moisture from the gas stream, but the purity may not be good enough for capillary GC use.
Fourth, be sure to use high-purity water to fill the generator; any volatile contaminants will eventually find their way into your inlet system and column.
Fifth, when using an FID with H2 carrier, try to run the column in constant flow mode. This will avoid column temperature-program changes in the total H2 flow through the detector that might affect its sensitivity.
Sixth, if you are using a mass-specrometric detector, remember that H2 pumping with turbomolecular pumps is less efficient than He pumping -- check the vacuum level to be sure that it is low enough.
Finally, do a cost analysis to be sure that the additional cost of using the generator for carrier gas doesn't cost a lot more than using tanks -- unless of course you can't use tanks due to your local safety regulations.
By Dan Vassilaros on Friday, July 16, 1999 - 07:04 am:
Be aware that the ion gauges and the gauge tubes used to measure vacuum in a mass spectrometer are calibrated against nitrogen. They do not give accurate values for helium and hydrogen. Perhaps John could give us an idea of how far off the readings really are.
Another point on the hydrogen generators. Some manufacturers use a paladium membrane to separate gaseous H2 from O2 after they are generated by the electrolysis cell. This membrane is highly selective for H2 and produces a very pure stream of H2 gas, but because it is a membrane, it also puts an upper limit on the total flow volume.
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