The unit “slyke”
The “slyke” is used to quantify the buffer value. The buffer value b was defined by Van Slyke 85 years ago by the differtial equation b=–dC/dpH [Van Slyke 1922], where dC is the infinitesimal small amount of the titrator used (acid/base) and dpH is the infinitesimal small change in pH caused by the addition of the titrator. For practical reasons the buffer value b is calculated as difference quotient b=–(c1-c2/pH1-pH2) which simplifies to b=–DC/DpH where Dc is the amount of the titrator used (acid/base) and DpH is the measured change in pH caused by the addition of the titrator. The slyke has the unit mol/l´pH. Since then the differential equation that van Slyke used to describe the buffer value has found its way to chemistry textbooks under the name “Van Slyke Formula” (also in other notations). In dentals sciences unfortunately the buffer value was anyhow measured in a wide variety of scale units that were incompatible among each other and lead to much confusion. Therefore Izutsu, 28 years ago, suggested standardizing the scale unit for the buffer value by accepting mol/l´pH. He further suggested renaming the unit mol/l´pH to slyke to honour the fundamental work of van Slyke. With this suggestion Izutsu had definitely solved the incompatibility of problem, which was, at least from my point of view, a very important step for the measurement of the buffer value in dental sciences. However if you go to the literature you will recognize that the buffer value still is given in many different incompatible scale units. For future studies it is important that they have a solid base that is anchored in literature. From my point of view there is no better anchor than van Slyke and Izutsu. In the end the slyke may appear as “unknown” or “exotic” scale unit for the buffer value, but the slyke is the most accurate scale unit to express the buffer value.
Van Slyke D: On the measurement of buffer values and the relationship of buffer value to the dissociation constant of the buffer and the concentration and reaction of the buffer solution. J Biol Chem 1922; 52:525-570.
Izutsu KT: Theory and Measurement of the buffer value of bicarbonate in saliva. J Theor Biol 1981;90:397-403.