[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]

Technically titration with a strong base could do the trick.

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.

[Borek]

Nicotine can be protonated twice, doesn't it?

[pcm81]

Nicotine can be protonated twice, doesn't it?

I am not sure. But if so, wouldn't I see the second knee at 2x the volume of NaOH of the first knee? Wikipedia states that nicotine is readily oxidized, so I wonder if KMnO4 could be another option for titrant.

[Borek]

You may have some impurities that react together with the second proton.

Googling for "determining nicotine by titration" gives plenty of hits.

[pcm81]

You may have some impurities that react together with the second proton.

Googling for "determining nicotine by titration" gives plenty of hits.

I looked at the google results before posting this thread. All titration kits and methods i've seen deal with freebase nicotine, which gets converted to nic salt with acid, so titrations are basically strong acid reaction with freebase nic. In my case i am starting with nic salt.

Could PG or VG be contributing to 2nd portion?

[Borek]

I looked at the google results before posting this thread. All titration kits and methods i've seen deal with freebase nicotine, which gets converted to nic salt with acid, so titrations are basically strong acid reaction with freebase nic. In my case i am starting with nic salt.

That's about acid base titrations, have you tried to look for other methods? You suggested permanganate - this is done in low pH, so the nicotine gets protonated, doesn't matter what form it was in initially.

Could PG or VG be contributing to 2nd portion?

Have you tried to estimate concentration of the nicotine and solvents, and compare it to the result obtained? You have 1.44 g of the solution and tens of mg of nicotine, does it add up?

[wildfyr]

Nicotine can certain by protonated twice. Did no one chekc the structure? Tertiary amine and a pyridine. The HCl salt is probably a dual HCl.

[pcm81]

I looked at the google results before posting this thread. All titration kits and methods i've seen deal with freebase nicotine, which gets converted to nic salt with acid, so titrations are basically strong acid reaction with freebase nic. In my case i am starting with nic salt.

Have you tried to estimate concentration of the nicotine and solvents, and compare it to the result obtained? You have 1.44 g of the solution and tens of mg of nicotine, does it add up?

The estimated concentration of nicotine in solvent is 24mg/ml (assuming nic salt manufacturer actually sold me 48mg/ml nic as advertised). The value i get from titration by NaOH is 26mg/ml from the first equivalence point... Don't know how to interpret or what to do with 2nd equivalence point.

I guess i'll try with H2SO4 and/or HCl tomorrow to see if i get similar results. Need to create standard solutions first though... I was worried about titrating with strong acid, just like a freebase nic, because of, to me unknown effect by acetic or benzoic acid. But since their pKa is around 4, i guess they'll pick up H+ from HCl nicely, in effect leaving ph unchanged until equivalence point.

All videos for nic titration kits i saw online stated that it is for freebase nic only, not for nic salts; and all these kits were HCl based... so i did not think far enough...

[wildfyr]

The number of moles is of nicotine is the number of moles of NaOH needed to titrate to just past the second equivalence point, at pH=10 or so. First the pyridine ring is deprotonated, then the tertiary amine is.


**edit I misspoke, if you are finding this thread years later, please see my next reply

[pcm81]

The number of moles is of nicotine is the number of moles of NaOH needed to titrate to just past the second equivalence point, at pH=10 or so. First the pyridine ring is deprotonated, then the tertiary amine is.

Thanks. If i do this calculation AND assume molar mass of just nicotine, not the nic salt, i get 24mg/ml, which is exactly what it theoretically should be. I guess when nic salt manufacturer lists 48mg/ml concentration they mean concentration of mass of actual nic, not nic salt...

[wildfyr]

Just want to be clear since I misspoke, though you seem to have it figured out. The number of moles of nicotine is the number of mols of NaOH needed to neutralize the first equivalence point. The number of moles to neutralize it all is the amount of HCl in there. There is no need to check the second equivalence point, except perhaps to see if it matches the first and will confirm its reliability.