Alternative buffer for PBS?

• A. Aged distilled water
• B. Normal saline
• C. Ethanol
• D. Ringer's solution

Answer: (A)

Buffering capacity is what keeps a solution’s pH from shifting when small amounts of acid or base are added. PBS is designed as a buffered, isotonic saline solution, typically using phosphate to hold the pH around 7.4. Of the options given, aged distilled water is the only one that can offer any buffering effect at all, because as it sits exposed to air CO2 dissolves into the water and establishes a very weak carbonic acid/bicarbonate system that resists minor pH changes. The other choices do not provide a true buffering pair or mechanism: normal saline is just salt in water without a buffer; ethanol is a solvent, not a buffering system; Ringer’s solution is an electrolyte mix but does not contain the phosphate buffering that PBS relies on. So aged distilled water is the best among the options for a rough, very weak buffer in this context, though it’s not a reliable substitute for a proper buffer like phosphate buffer.