[Borek]

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.

Actually whether one should use amount of base used to reach the first endpoint or the amount of base used to move from the first endpoint to the second endpoint may depend on the impurities present. If the impurities contain some weak acid, it can get neutralized earlier (increasing amount of the base necessary to reach the first endpoint), or later (together with the second nicotine proton and increasing amount of the base necessary to reach the second endpoint).

If both endpoints use exactly the same volume of titrant that's the best situation (most likely nothing else but nicotine reacts). If the volumes are different I would choose the lower one for calculations.

As amount of PG/VG is at least order of magnitude larger if they were reacting during titration amount of base required to reach one of the endpoints would be also an order of magnitude larger.

[pcm81]

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.

Just to clarify for future readers. There is no HCl, in the sample I titrated so far. The sample is nicotine salt with acetic or benzoic acid. I believe mine is with benzoic acid.

I intend to titrate it with HCl to see if I get the same answer, but that probably won't be very soon. Need to get clean HCl first... mine is pool cleaner.

[wildfyr]

Ah ok. I guess that makes sense since its being inhaled. Often, drugs are HCl salts.

[pcm81]

Picked up some HCl on the way home at lowes. Doing a ghetto tub purification tonight.Will try HCl titration later and report results. Meanwhile want to make sure i understand the HCl titration chemistry:

Starting solution has VG/PG and Nicotine salt, which is nicotine combined with benzoic or acetic acid. Potentially there is also free nicotine or free acid. I believe my salt is based on benzoic acid.
When I add HCl what i actually get are:
1. PG
2. VG
3. H+ and Cl-
4. Nic+benzoic

The equilibria at play are:
1. Nic-Benzoic vs free nic+ and free benzoic- (this will go all the way to the right, b/c free benzoic- keeps getting protonated in 2.)
2. free benzoic- vs protonated benzoic (this will go towards protonated b/c its a weak acid and H+ is abundant from 3)
3. HCl vs H+ and Cl- this will go all the way to the right since HCl is strong acid
4. Nic-Cl vs free nic+ and free Cl- This will go all the way to the left due to abundance of Cl-


During titration, pH will fall and the titration point with steepest slope is when all benzoic acid has been protonated, hence giving me amount of benzoic acid present.

Does this sound about right?

Also, what should i expect to see in the event if solution has excess of nicotine or excess of benzoic. Isn't pH equivalence point basically giving me concentration of benzoic acid, so nicotine concentration is only determined by assumption that it is equal to concentration of benzoic acid?

On second thought, any benzoic acid not bound to nic is already protonated, since it is a weak acid, so titration would measure amount of benzoic bound to nic. But this still leaves the question of excess free nic preset.

[aarontayto]

Hi,

Did you ever figure out a way to do a titration test on nic salt based e-liquid?

Thanks!

Aaron

Picked up some HCl on the way home at lowes. Doing a ghetto tub purification tonight.Will try HCl titration later and report results. Meanwhile want to make sure i understand the HCl titration chemistry:

Starting solution has VG/PG and Nicotine salt, which is nicotine combined with benzoic or acetic acid. Potentially there is also free nicotine or free acid. I believe my salt is based on benzoic acid.
When I add HCl what i actually get are:
1. PG
2. VG
3. H+ and Cl-
4. Nic+benzoic

The equilibria at play are:
1. Nic-Benzoic vs free nic+ and free benzoic- (this will go all the way to the right, b/c free benzoic- keeps getting protonated in 2.)
2. free benzoic- vs protonated benzoic (this will go towards protonated b/c its a weak acid and H+ is abundant from 3)
3. HCl vs H+ and Cl- this will go all the way to the right since HCl is strong acid
4. Nic-Cl vs free nic+ and free Cl- This will go all the way to the left due to abundance of Cl-


During titration, pH will fall and the titration point with steepest slope is when all benzoic acid has been protonated, hence giving me amount of benzoic acid present.

Does this sound about right?

Also, what should i expect to see in the event if solution has excess of nicotine or excess of benzoic. Isn't pH equivalence point basically giving me concentration of benzoic acid, so nicotine concentration is only determined by assumption that it is equal to concentration of benzoic acid?

On second thought, any benzoic acid not bound to nic is already protonated, since it is a weak acid, so titration would measure amount of benzoic bound to nic. But this still leaves the question of excess free nic preset.

[h67aruki]

Hello,

the topic you have raised is very interesting for me. I have been looking for a long time for a way to measure nicotine concentration in nicotine salts, among other things, using a tritation - with no success. I would be extremely obliged if you would share the results of your 2019 experiments Perhaps you managed to obtain satisfactory results? There are currently several types of nicotine salts on the raw materials market: benzoate, lactate, salicylate, for example.
Thanks in advance.

Regards, Marcin

Picked up some HCl on the way home at lowes. Doing a ghetto tub purification tonight.Will try HCl titration later and report results. Meanwhile want to make sure i understand the HCl titration chemistry:

Starting solution has VG/PG and Nicotine salt, which is nicotine combined with benzoic or acetic acid. Potentially there is also free nicotine or free acid. I believe my salt is based on benzoic acid.
When I add HCl what i actually get are:
1. PG
2. VG
3. H+ and Cl-
4. Nic+benzoic

The equilibria at play are:
1. Nic-Benzoic vs free nic+ and free benzoic- (this will go all the way to the right, b/c free benzoic- keeps getting protonated in 2.)
2. free benzoic- vs protonated benzoic (this will go towards protonated b/c its a weak acid and H+ is abundant from 3)
3. HCl vs H+ and Cl- this will go all the way to the right since HCl is strong acid
4. Nic-Cl vs free nic+ and free Cl- This will go all the way to the left due to abundance of Cl-


During titration, pH will fall and the titration point with steepest slope is when all benzoic acid has been protonated, hence giving me amount of benzoic acid present.

Does this sound about right?

Also, what should i expect to see in the event if solution has excess of nicotine or excess of benzoic. Isn't pH equivalence point basically giving me concentration of benzoic acid, so nicotine concentration is only determined by assumption that it is equal to concentration of benzoic acid?

On second thought, any benzoic acid not bound to nic is already protonated, since it is a weak acid, so titration would measure amount of benzoic bound to nic. But this still leaves the question of excess free nic preset.

[h67aruki]

Hello,

in an act of desperation I have pulled out one method using AI. I have no idea if it is correct, if it gives a chance for a meaningful study, etc. Nevertheless, I am sending what I received from Claude.ia:

# Reverse titration of nicotine salts

1. Sample preparation:
- Dissolve a known amount of nicotine salt in distilled water.

2. Add excess acid:
- Add a known excess amount of a standard strong acid solution (e.g. HCl).
- This acid will react with the nicotine salt to release free nicotine.

3. Titration of excess acid:
- Titrate the solution with a standard alkali solution (e.g. NaOH).
- Use a pH meter to monitor pH changes.

4. End point:
- The end point is when all excess acid has been neutralised.
- Visible as a sudden change in pH on the titration curve.

5. Calculation:
- Calculate the amount of acid that has reacted with the nicotine (difference between the acid added and that neutralised by NaOH).
- Calculate the nicotine content of the sample on this basis.

6. Quality control:
- Analyse the blank and samples with known nicotine concentration.
- Calculate the recovery and precision of the method.

Note: This method may be particularly useful when direct titration of nicotine salts is difficult, e.g. due to poor solubility or interferences.

Regards, Marcin

[Borek]

In general I don't trust AI, but you can't be completely wrong on such a general level, unless the pKa is not in the right range for reverse titration, and unless counterion interferes. Hard to say without doing a better analysis of the theoretical titration curve (and even then it can only suggest the procedure being wrong, it can't prove the titration is doable).

[h67aruki]

We will try to test this this week and determine the usefulness of this method. I hope that its description is not the result of an AI dream ; )

Regards, Marcin