Biochemistry. A buffer solution containing sodium chloride (NaCl), potassium chloride (KCl), sodium phosphate (Na2HPO4), and potassium phosphate (KH2PO4). PBS has a pH of 7.2 - 7.4 that matches the human body (isotonic). The buffer PBS helps to maintain a constant pH in biochemistry experiments. PBS is often used in cell biology experiments to maintain the osmolarity of the cells.