The problem is that when I drop the oil it comes out of the needle's hole and rises up the sides of the needle forming a horrible drop that can't be measured. Normally needles are clean (I am cleaning them every time), have verticality, and are more or less OK. Should I maybe spread some glycerol in the needle sides?
Glycerol is risky as may wet the tip/ inside of the needle.
I assume that you have a needle cut perpendicular to the hole and not at an angle as used for injections. If not this may be the problem.
Otherwise the problem is wettability, and the needle is not completely clean. Try heating the tip until almost red and this will burn all residual organic material, then wipe the outside with Methanol.
I never tried but using a very fine sand paper or other material to create a rough surface on the outside may help reduce the rise .
Thank you for your answer, I will try this with steel needles (I've already try with heating needle but it didn't worked). For the moment I'm using Teflon needles that work well. Thanks again.
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