I think it would be nice to have one topic about this very useful technique. There is quite a lot of information about it on Nexus, but it is scattered, so let's correct this.

You can find how I do it in this initial post. It may be done differently for sure, but let's keep it simple. If you understand the whole process, you can change/tweak it as you wish.

Anyone is more than welcome to ask if anything is unclear, add any valuable information bellow or correct anything I write in an error. I am not chemist, so do not expect exact scientific language.

(Back-)salting

First let's explain (back-)salting: it is a way how to convert alkaloids in freebase form to its salt form. Usually it is done by addition of (distilled) water and then by addition of diluted acid. In our case HCl, but any other acid can be used. However, emulsion compatibility has to be checked. Everything is stirred/shaken thoroughly, and the alkaloids transfer from non-polar solvent to water. We are using the fact the alkaloids are soluble in non-polar solvent and insoluble in water when in freebase form and soluble in water and insoluble in non-polar solvent when in salt form. But please bear in mind, this solubility and insolubility is not absolute. Especially for mescaline.

Titration

Titration is (for our purposes) a form of controlled salting which allows reaching desired pH level and provides the tool for making alkaloids content estimates. It is iterative process, in which we are adding small amount of diluted acid, not all acid at once. After each addition of acid and proper mixing/shaking we check pH. If it is basic (>7) then there are still alkaloids in freebase form and we continue with next iteration. If it is neutral (7) then most of the alkaloids are in the salt form, when slightly acidic (about 5), then all the alkaloids have been transferred and are in the salt form. If we stop at neutral pH (7) or slightly acidic pH (5-6) depends on our strategy. If we plan to purify mescaline later, then we go lower. If we want the purest result, because we are not planning to purify further (suggested though), we stop at pH 7.

Simply : the more acid needed, the more alkaloids are there!

Only one titration “pull” is necessary. The mescaline is transferred very readily from freebase to salt.

The pH moves slowly from basic to neutral. When neutral, it needs only very little acid to get acidic. If we know how much acid we've added to reach pH 6-7, we can say/calculate how much alkaloids are in the solution.

Note : If one would like to titrate DMT with HCl (works very well), he might be surprised that the pH curve while titrating is different from mescaline. For mescaline the curve is much more steep, pH is more basic at the beginning and comes down to neutral and acidic levels during the titration. For DMT the pH curve is much more flat. It is slightly basic, almost not changing during whole titration. At the end it suddenly falls down to neutral and acidic levels.

Detailed process

1. Prepare HCl of desired concentration in small flask. Something between 1%-3,8% is convenient. If I have 37% HCl, I just mix one part of HCl and 9 parts of distilled water, so I get about 3,7% HCl
2. Find out how much acid of given concentration you need for estimated minimal mescaline amount in non-polar solvent. This can be calculated in HCl Titration Calculator
3. Divide the amount by let’s say 4. It can be less, it is up to you how precise you want to be. If you use less acid, it will be more precise, but more work (more iterations) will have to be done. If you use more acid, less work is necessary (less iterations), but it is likely you will overshoot the pH and the result will be impure or estimate will be too rough
4. Put non-polar solvent with alkaloids into the glass, preferably erlenmeyer flask, but can be separation funnel or another vessel. Erlenmeyer flask is convenient, because you can mix vigorously, and it stays in the flask. The size of flask should be such that 1/4 to 1/3 of the flask is filled with both non-polar solvent and water (see bellow). Too much water in the flask complicates mixing
5. Add about 1/4 to 1/3 of distilled water compared to non-polar solvent
6. Heat up to 60-80C. Hot tap water might be enough, or use water bath
7. Take the acid amount from step 3 and put it into the flask. The best is glass pipette, I am using 10ml graduated pipette with small outlet. Pipette is used without rubber bulb. Remember total amount of acid in the solution
8. Mix thoroughly, at least few minutes. Then let settle. Make sure there is no emulsion
9. Take another long glass pipette, I am using 2ml. Take sample of the bottom aqueous layer. Make sure there is not non-polar solvent in the pipette, just the water. I usually lean the flask, wait to settle, insert pipette, blow a bit to make sure there is no non-polar solvent in the pipette and suck the water into the pipette
10. Put some sample water back into the flask, to make sure there is not non-polar solvent in the pipette. Sprinkle water sample onto pH paper and check the color. Put the sample from the pipette back into the flask.
11. pH papers color:
- Basic (pH>7) => Repeat steps 7-11.
- Neutral =>
.....If subsequent purification is planned => Repeat steps 7-11.
.....If no further purification is planned => Don’t go under 7, as more impurities would get into aqueous layer. Continue by next step
- Acidic (pH 5-6) => Continue by next step
12. Separate aqueous layer from non-polar solvent. I just use beaker for pouring off the solvent as much as possible. Then I use glass funnel with cotton blocking the output. I use turkey baster to take the bottom water from beaker (with water and tiny np at the top). I suck only water, no np. Turkey baster is used, because I don't want any np to touch the cotton. Once the funnel is almost full, I release a bit the cotton by tiny wooden stick, so it starts to go slowly through. Then I slowly pour all the water + a bit of np from the beaker to the funnel. I don’t forget to wash out the beaker, so I don’t lose anything. The np stays at the top, so I am sure only water goes through. Once np should go through, I remove the funnel.
13. Take the total amount of used acid from step 7. Put it into calculator (with correctly set HCl concentration) and voila … we get how much mescaline freebase is within our aqueous layer!
14. Now non-polar solvent can be reused for next pull (if the value from step 13 is still high enough) or stored for next extraction (if the value from step 13 is low and it is not worth next pull).
Aqueous layer is collected and merged with aqueous layer from titration(s) of previous or next pull(s). Then it is evaporated and processed further.