THE DETECTION OF SALTING-OUT - A COMPARATIVE-STUDY

We present a new device developed in our laboratory for the detection of salting-out, witch can be also used for the measurement of the metastable zone width and related parameters, under controled conditions of temperature and supersaturation. The interest of this apparatus came from the fact that the salting-out is detected by using simultaneously up to seven different methods: a) visual detection, b) intensity of the transmitted laser beam, c) noise associated to (b), d) conductivity, e) intensity of the reflected laser beam, f) noise associated to (e) and g) pH. Full computerization permits an easy and quick take of data on the evolution of the nucleation and crystal growth processes. Typical data input rates are 20 sec-1 * channel-1, but this variable can be selected by the operator. The use of this apparatus for the study of the cooling behavior of Potassium Bitartrate water solutions shows that the waiting time for the growth component of the salting-out is minimized for the method using the noise associated to the reflected light as the recorded parameter. Moreover, this comparative study shows that the maximum undercooling and maximum allowable supersaturation values obtained by the different tested methods present significant differences one each other. Such a disagreement could introduce troubles in the calculation of the experimental nucleation order, the relevant parameter for the theoretical approach to industrial crystallization problems. Meanwhile, we propose that the tabulated values of such parameters should specify the experimental way followed for the obtention of reliable data.