Phosphate buffered saline (PBS) is a buffer solution containing sodium chloride, sodium phosphate, and in some formulations potassium chloride and potassium phosphate. PBS helps to maintain a constant pH and is isotonic and non-toxic to cells. This formulation does not contain calcium and magnesium. Phosphate buffered saline (PBS) is a buffer solution containing sodium chloride, sodium phosphate, and in some formulations potassium chloride and potassium phosphate. PBS helps to maintain a constant pH and is isotonic and non-toxic to cells. This formulation does not contain calcium and magnesium.