At the start of your process (I would say it is absorbtion, not adsorbtion, since the gas will be disolved in the whole liquid volume but not retained only at the surface) you may add few drops of a pH indicator that changes its color around neutral pH range. I recommend brom thymol blue indicator that has such change at pH around 7, more exactly from blue (alkaline) to yellow (acid). Thus, you will know when the alkaline solution is exhausted due to CO2 absorbtion that makes the absorbant become acid. This will be the good time to replace the alkaline absorbant.

Even after 50 days it is not late to add an indicator and see if the solution became acid/exhausted. Phenolphthalein is also good for this check around neutral, the incolor alkaline solution will become pink in acid environment (due to absorbed CO2, H2S).

Sorry, I was wrong about phenolphtalein color, it is pink in alkaline and will become incolor in acid.

Thank you so much dear madam for your explanation and as well to use absorption rather than adsorption. I have used phenolphthalein as an indicator, it turns color in blue. Yes it's color is still same as it was at the beginning.

Furthermore I would like to ask that can we quantify the CO2 and H2S absorption from the same solution?

Thank,

Asim

dear Asim, read this article about the use of alkaline traps in volcanic envinment to determine F,Cl and SO4. The efficiency of the trap decrease with time respect these gases and , in my opinion, also respect CO2 and trace elements.

guenda

Thank you dear Guenda, yes may be the same phenomena happens in this case as well. Dear Guenda, did you quantify the amount of traps?

Thanks,

Asim

we used 4 traps around the fumarolic field

Use lead acetate paper or solution exposed to fumarolic gases. Many other ways of absorbing H2S quantitatively.

Thank you sir for your response....

Asim