Most common buffer used for PBS?

• A. Sodium phosphate
• B. Sodium chloride
• C. Potassium phosphate
• D. Tris

Answer: (A)

Phosphate buffer is what defines PBS. The buffering component comes from the phosphate system, using salts of sodium phosphate to create a conjugate pair of H2PO4− and HPO4^2− with a pKa near physiological pH. This lets the solution stay around 7.4 when mixed in the right ratio, which is ideal for preserving biological samples. Sodium phosphate provides the buffering action, while other salts like NaCl supply the isotonic saline environment. Tris is a different buffering system used in other buffers, not the standard PBS. Potassium phosphate can be used in alternative formulations, but the classic, most common PBS uses sodium phosphate.