Godin:Protocols/Buffer Solutions

Materials

• Potassium Chloride (KCl) (BP366 - Fisher Scientific)
  • MW = 74.55 g/mol
• Lithium Chloride (LiCl) (L121 - Fisher Scientific)
  • MW 42.39 g/mol
• HEPES buffer (BP310 - Fisher Scientific)
  • MW = 283.3 g/mol
• EDTA (431788 - Aldrich Chemistry)
  • MW = 292.24 g/mol
• Potassium hydroxide (KOH) from Science Store
  • MW = 56.11 g/mol
• HEPES (BP310 - Fisher Scientific)
• Filtered deionized water
• Vacuum filtration system (1 μm pore size)
• pH/conductance meter

Preparation

• Aqueous salt buffer (pH 8.0)

1. Partially fill a clean receptacle to slightly less than the final desired volume.
2. Measure out salt and buffer powder (and optionally 1 mM EDTA) and add to DI water (see table 1 below).
3. Fill to final desired volume with DI water.
4. Add magnetic stir bar and mix until completely dissolved.
5. Bring the solution to the desired pH by adding 2 M KOH dropwise while monitoring with a pH meter.
6. Obtain a conductance measurement.

Solution	Volume	Mass of salt (g)	Mass of buffer (g)	Mass EDTA (g)
1 M KCl, 10 mM HEPES	500 mL	37.275	1.417	0.146
2 M KCl, 10 mM HEPES	500 mL	74.55	1.417	0.146
3 M KCl, 10 mM HEPES	500 mL	111.827	1.417	0.146
1 M LiCl, 10 mM HEPES	500 mL	21.197	1.417	0.146
3.6 M LiCl, 10 mM HEPES	500 mL	76.31	1.417	0.146
4 M LiCl, 10 mM HEPES	500 mL	84.788	1.417	0.146

*To make aqueous salt buffer - pH 10.0 "HEPES" should be replaced by "Sodium Bicarbonate (NaHCO3)". Fore this purpose 0.42 g should be added to 500 mL of the solution.

• 2 M KOH (100 mL)

The following should be performed in the fume hood wearing full PPE

1. Measure 11.2220 g of KOH
2. Add 100 mL of deionized water.