It depends on your output rate - on my small electrolyzer (5 cm2), the rates were still enough for an injector port in the output tubes to work (clear t-junction with a septum to inject through - or just a section of clear nalgene tubing you're okay replacing periodically). You need a locking, gas-tight syringe - I purge it with nitrogen from a bag (also with an injectable septum - to not overload the column with hydrogen or oxygen, typically you need to dilute it with nitrogen anyway) beforehand and put a small ball of cotton between the needle and the syringe body to soak up water if I do hit some/reduce water vapour.

I'm sure you could accomplish the same thing easily enough by not using a smaller vessel than a burette for the water displacement, but the gas-tight syringe is a must.

Thanks Mr. Benjamin

Dear Mr. Artur, gas is collected at the upper portion of the burette by displacing the water. But how to collect the gas accurately for GC analysis if we want to study the time to time production of hydrogen.

Thanks Dr. Artur