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I'm trying to find a proper buffer for my experiment, which I'd appreciate some suggestions on. I have a solution in which I want to measure the concentration of magnesium ions using a fluorescent probe, which needs to be buffered at pH 6-7 (preferably the lower end).

The probe is dissolved in ethanol, and will be mixed with an acidic, aqueous sample of magnesium. As the probe only functions at pH 6-7, I need to buffer the ethanol back to this pH. I noticed the Goods' buffers are almost ideal for this application, except they are meant to be soluble in water, not ethanol.

Is there any specific category of buffers that dissolve well in ethanol? Or does anyone know any papers/protocols that describe e.g., a synthesis route to increase the solubility of e.g., PIPES or HEPES in ethanol?

Note: I prefer to buffer the ethanol solution rather than adding e.g., NaOH as I need to keep the added water to a minimum (it quenches the fluorophore).

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    $\begingroup$ What is the ratio of ethanol(probe) and water(acidic Mg solution)? Why not to buffer the water solution? pKa and pH of buffers are implied for water, not other solvents. $\endgroup$
    – Poutnik
    Commented Jun 10 at 10:00
  • $\begingroup$ @Poutnik: I agreed with you. fluorescent probe works in very dilute conditions so we usually dissolve them in suitable organic solvents in minimum volume and dilute it to required concentration using water (in here, using suitable buffer solution). $\endgroup$
    – Mathew Mahindaratne
    Commented Jun 10 at 17:09

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