HEPES-buffered saline

140 mM NaCl

1.5 mM Na₂HPO₄•2H₂O

50 mM HEPES

For a 2x solution: Dissolve 0.8 g of NaCl, 0.027 g of Na₂HPO₄•2H₂O, and 1.2 g of HEPES in a total volume of 90 ml of distilled H₂O. Adjust the pH to 7.05 with 0.5 n NaOH, and then adjust the volume to 100 ml with distilled H₂O. Sterilize the solution by passing it through a 0.22-μm filter; store the filtrate in 5-ml aliquots at -20°C for periods of up to 1 year.