An improved method to validate the relative humidity generation in sorption balances

Sorption balances are instruments in which samples are weighed as they are exposed to a programmed relative humidity (RH). Such instruments are used to measure sorption isotherms and to study solid-vapour interaction. There are different methods to validate the performance of the RH generation in such instruments by charging them with saturated salt solutions and ramping/stepping the RH past the deliquescence RH of the salts. In this paper an improved approach to perform validation is presented where the RH is kept stepwise constant at a quasi-randomly chosen set of RH-values above and below the deliquescence RH. From the rates of change of mass as a function of RH it is possible to calculate the RH at which deliquescence takes place. This alternative method gives similar results as the slow ramp method, but is less sensitive to disturbances and less time consuming.