There's a similar knack towards separation of alkaloids from a mixture to be seen with the ongoing harmala alkaloid separation efforts over in the exceptionally instructive
...finetuning of the VDS-protocols thread. There's the application of carefully controlled pH levels to facilitate separation of some quite similar alkaloids. Whether that method could be applied to a mixture of cactus alkaloids depends to a large extent on the relative pK values of the individual alkaloids. Not to mention a component of enthalpies of crystallization. You can't guarantee that the mescaline will be pulled first without some research, both literature and practical.
Then there's the exploitation of differential solubility parameters, hence the use of acetone and MEK washes.
And before you know it, you're contemplating preparative chromatography
The thing about citric acid (besides its hydroxy group...) is that it can combine with 3, 2 or 1 equivalents of univalent base - such as a protonated monoamine - which may make the pH curve unfavourable for obtaining sharp separations.
“There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli