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Nicotine salt titration

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pcm81:
Can the concentration of nicotine salts in VG/PG solution be measured by titration? I believe there are titration kits for freebase nicotine based on HCl or H2SO4, however since nicotine salts are already nicotine combined with acid, (I believe acetic acid) I guess i'd need some other titrant.

Borek:
Technically titration with a strong base could do the trick.

pcm81:

--- Quote from: Borek on May 26, 2019, 07:15:37 PM ---Technically titration with a strong base could do the trick.

--- End quote ---

Thanks.
I suspected that, but was not sure about other reactions with VG and PG. I guess I'll try NaOH and see what pH curve i get.

pcm81:
I did a quick titration vs NaOH, but i am surprised with results.
I see a 2-knee curve. Here are the data points:
NaOh ml   pH
0   4.14
1   4.37
2   4.63
3   5.08
3.5   5.46
4   6.78
4.3   7.11
4.5   7.25
4.7   7.37
5   7.51
5.25   7.68
5.5   7.75
5.8   7.84
6   7.92
6.5   8.07
7   8.23
7.5   8.39
8   8.54
8.5   8.74
9   9
9.5   9.55
10   10.44
10.5   10.88
11.5   11.2

Left column are ml of 0.03 molar NaOH and right column is pH vs a 1.44g solution of nicotine ejuice base. I took 1.44g of 50%PG/50%VG solution of what should be 24mg/ml of nic salts. Added volume of water to cover ph probe and titrated vs NaOH.

I am surprised to see 2 knees (equivalence points)

pcm81:
At the first knee i get 0.0001146 moles on NaOH. Assuming 1:1 ratio to nic salts and the nic salt molar mass of 222.23 (162 for nicotine and 60 for acetic acid) i get 20.33mg/ml nic salt concentration from 1st titration equilibrium point. if i assume benzoic acid being used to make nic salt in place of aceitic, then salt molar mass becomes 284.35 and i get 26mg/ml of nic salts. I was expecting to see 24mg/ml from nic salt. This nic salt started as 48mg/ml in VG solution, which i cut by equal volume of PG so should be 24mg/ml of nicotine salt with density of 1.15g/ml (average of 1.04 for PG and 1.26 for VG)

What confuses me is the existence of 2nd knee.

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