PBS, or Phosphate-Buffered Saline, is a very commonly used biological buffer solution due to its non-toxic properties and similarities with human biological fluid. Its basic recipe comprises of sodium chloride, sodium phosphate, and potassium phosphate dissolved in water. The ideal pH is 7.4. Variations of PBS may change salt concentrations, as well as the addition of potassium chloride, calcium, or magnesium, or detergents such as Tween. PBS is commonly used in preparations involving cells, such as washing, staining, or diluting.