Hello fellow Patchers and Sealers,
I made a pipette solution recently and expected the osmolarity to be around 270 mOsm approximately according to rough calculation but when I measured it it was only about 191 mOsm. I am pretty confident I did not miss out on any ingredients or added more water that could decrease the osmolarity than expected. Now, at this point, I am requestioning my manual calculation of 270 mOsm (approx) from the recipe. It would be really helpful if someone can proof-check my calculation for the recipe below. Just the K- gluconate itself should make it 244 mOsm to begin with.
NOTE: To adjust the pH to 7.4 I had to add about 1 mL of 1M KOH. I wonder if this could be a reason. I doubt it though since only an mL of this in a 100 ML final volume should not make the difference.
Recipe: K-Gluconate 122mM, NaCl 9mM, MgCl2 1.8 mM, Mg-ATP 4mM, Na-GTP 0.3 mM, Creatine phosphate 14mM, EGTA 0.45 mM, CaCl2 0.1 mM, HEPES 10 mM
Dear Maibam,
gluconic acid is weak so its dissociation is incomplete in water. You should increase the amount of K-Gluconate or another component of your solution in order to reach the desired osmolarity.
Thanks Mario. I was able to make a pipette solution with the desired osmolarity.
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