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Topic: Nicotine salt titration  (Read 784 times)

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Offline Borek

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Re: Nicotine salt titration
« Reply #15 on: May 28, 2019, 02:52:18 AM »
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.
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Offline pcm81

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Re: Nicotine salt titration
« Reply #16 on: May 28, 2019, 09:27:28 AM »
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.

Offline wildfyr

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Re: Nicotine salt titration
« Reply #17 on: May 28, 2019, 10:42:23 AM »
Ah ok. I guess that makes sense since its being inhaled. Often, drugs are HCl salts.

Offline pcm81

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Re: Nicotine salt titration
« Reply #18 on: May 28, 2019, 06:50:39 PM »
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.
« Last Edit: May 28, 2019, 07:13:18 PM by pcm81 »

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