Advanced Question regarding Drug Solubility at Different pH's

[Captain.Heroin]

According to this source, alprazolam's water solubility is

40 mg/L at pH 7; 12 mg/mL at pH 1.2

My question is the following...

knowing these two things, could one extrapolate a solubility point for different pH's? Or is it something that would require further experimenting?

Without having to acquire a pH meter or anything like that, how can you create a solution at 1.2 pH?

I found out that white distilled vinegar on its own should have a pH of 2.4. What would alprazolam's solubility in white distilled vinegar be?

Is this something anyone can tell me? Thanks in advance.

 

[sekio]

knowing these two things, could one extrapolate a solubility point for different pH's? Or is it something that would require further experimenting?

You'd have to experiment, solubility versus pH is not always linear. But a linear prediction is better than nothing.

Without having to acquire a pH meter or anything like that, how can you create a solution at 1.2 pH?

No offense, get a pH meter or pH papers if you want an accurate number. Otherwise you are restricted to measuring specific amounts of pure reagents and praying the acidity is right. (in that case, do the math for pKa times concentration)
Weak acids like citric and acetic acid will not dissociate fully into H+/B- and will be "less acidic" than an equimolar amount of, e.g. HCl.

An easy and rough way to get pH 1 is about 0.1M HCl in water, or 0.3% w/v. (1 part "concentrated" hydrochloric to 99 pts distilled, degassed, water). Stomach acid is about this strong.
If you are planning to dissolve alprazolam for injection, I would not go lower than maybe pH 5.

 

[polymath]

40 mg/L at pH 7; 12 mg/mL at pH 1.2

Also remember that more exactly put, this says "if the pH of alprazolam solution after the dissolution is 7, then at most 40 mg/L has dissolved". Dissolving alprazolam in water changes the pH from its initial value.