Dušan Veličković Author Answered Mar 8, 2018
Pacific Northwest National Laboratory
Hi Theodora,
Thanks for your questions!
Filter paper is used to saturate air in chamber with solvent vapor, so that sample doesn't dry there. In fact, filter paper absorbs the liquid in the solvent and provides more surface area for evaporation. More surface area=faster evaporation. More evaporation means more solvent vapor in the chamber's air.
A saturated solution of salt in water is used to maintain particular values of relative humidity inside chamber. K2SO4 gives the highest relative humidity. At 45C saturated K2SO4 has 96% relative humidity, which we used in our experiments. We tried also different salts solutions, but every time droplet of enzyme will not "survive" after overnight incubation. With K2SO4 we could incubate 24h without drying of enzyme droplet spotted on the tissue.
I hope this will help you in your experiments,
Dusan