Phosphate-Buffered Saline (PBS)

1× PBS

• 136.9 mM NaCl, 8.0 g/L
• 2.7 mM KCl, 0.2 g/L
• 27.8 mM Na/K phosphate buffers:
  • 10.14 mM Na₂HPO₄, 1.44 g/L (anhyd)
  • 17.64 mM KH₂PO₄, 0.24 g/L (anhyd)
• pH 7.4
  Molarities: 157.2 mM Na⁺, 139.6 mM Cl^–, 20.3 mM K⁺, 27.8 mM H_xPO₄

10× PBS

1. Combine the following:
   • 80 g NaCl
   • 2 g KCl
   • 14.4 g Na₂HPO₄ (dibasic anhydrous) OR 18.1 g Na₂HPO₄·2H₂O (dibasic dihydrate) OR 27.2 g Na₂HPO₄·7H₂O (dibasic heptahydrate)
   • 2.4 g KH₂PO₄ (monobasic anhydrous)
   • 800 mL diH₂O
2. Adjust pH to 7.4 with HCl.
3. Add diH₂O to 1 L.
4. Autoclave 15–20 min on liquid cycle. Store room-temp.

PBST

For some applications (washing), a detergent such as TWEEN 20 (polysorbate 20) or Triton X-100 are added to PBS to make PBST.

• Usual concentrations of TWEEN 20 in PBST are 0.05% or 0.1% = 0.5–1 g/L.
• Usual concentration of Triton X-100 in TBST is 0.1–0.3% = 1–3 g/L.