Tris-buffered saline (TBS) is a buffer used in some biochemical techniques to maintain the pH within a relatively narrow range. Tris (with HCl) has a slightly alkaline buffering capacity in the 7–9.2 range. The conjugate acid of Tris has a pK of 8.07 at 25 °C. The pK declines approximately 0.03 units per degree Celsius rise in temperature. This can lead to relatively dramatic pH shifts when there are shifts in solution temperature. Sodium chloride concentration may vary from 100 to 200 mM, tris concentration from 5 to 100 mM and pH from 7.2 to 8.0. A common formulation of TBS is 150 mM NaCl, 50 mM Tris-HCl, pH 7.6. TBS can also be prepared by using commercially made TBS buffer tablets or pouches.