Excellent thank you for running that test. I didn't think it was soluble but 3% yield is not a typical result. My only other concern was the initial one being the magnesium hydroxide precipitation. You weren't completely clear though, you did evaporate the solvent and there were no solid residues afterwards?

In your initial extraction are you sure that none of this milky emulsion was pulled alongside the alkaloid laden solvent? This would be an important thing to know. I assume you are tipping your experiment, if in a jar, end over end just like you would any other correct?

By removing hydroxide ions from the solution in the form of a precipitate this should lower the pH. To what extent I can't be certain but the majority of precipitation reactions tend to go towards completion. Also this means you are loosing ions and the supposed ionic effect is decreased. Which is why I don't know if MgSO4 is an ideal way to go about this.