The Relation between Adsorption of Additives and Crystal Growth Rate of L-Alanine

Abstract

The growth kinetics of L-alanine from solution in the presence and absence of L-phenylalanine and L-leucine has been studied. L-Alanine crystal growth, from crystal size distribution measurements, is independent of the agitation rate suggesting that the growth mechanism is surface controlled. The dependence of growth rate on supersaturation at constant additive concentration suggests that there is no change in the growth mechanism of L-alanine due to the presence of additive. The growth rate of L-alanine is reduced by 50% with a mol fraction of 5 x 10-5 of L-phenylalanine and 2 x 10-4 of L-leucine. The solubility of L-alanine is not significantly affected by the presence of these additives in solution. The effect of these additives on the growth kinetics is due to their adsorption onto the growing L-alanine crystals. The extent of this effect is satisfactorily explained assuming both that (i) the inhibition of the growth rate is proportional to the degree of surface coverage and that (ii) the crystal surface is homogeneous with respect to the energy of adsorption sites.