Optimal H2 Column Flow

Discussions about GC and other "gas phase" separation techniques.

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What is the optimal H2 flow rate for the following column dimensions?

0.25 mm
0.25 um

I can never remember where to find this info when I need it... Thanks.
That would depend on detection type and analysis. MS would require <1.5mL/min. FID or ECD could tolerate up to 3.0mL/min without loss of separation power. There are calculators online to help with this decision. I know Restek has one.

Start with a search for Van Deemter plots for carrier gasses. Those will give an idea of where to begin.

Also Restek has an online tool to transfer a current He carrier method to H2 carrier that works well. You just input the column information and your current oven and flow program for He and it will convert to H2 parameters.
The past is there to guide us into the future, not to dwell in.
If you want to go for speed, a rule of thumb that can be used is the "speed optimized flow" principle.

For helium: 8 x column ID (mm)
For hydrogen: 10 x column ID (mm)

So for your column and carrier, 2.5 mL/min can be used. This does not take into account detector limitations. If this is a good hydrogen flow to be used on an MS detector is a different question, I don't have hands-on experience using hydrogen as a carrier on GC-MS.

Source + further references
What Rndirk recommends is a good starting point. However, there are additional details. Optimal flow depends on column temperature and, in temperature-programmed GC, it is about 30% lower than in isothermal GC. All these and other details were discussed in:
L. M. Blumberg, Flow optimization in one-dimensional and comprehensive two-dimensional gas chromatography, Journal of Chromatography A, vol. 1536 (2018) pages 27–38.
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