Jan 22, 2018 · 2. Buffer Solution (10 mM Ammonium acetate aqueous solution): Pipet 100 mL Stock Solution into a 1000 mL volumetric flask and dilute to mark with DI water. This makes a 10 mM solution. 3. 90/10 Mixture: Pipet 100 mL Buffer Solution into a 1000 mL volumetric flask and dilute to mark with acetonitrile.