A simple method of determining the aqueous solubility of organic substances

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Abstract
A new method is described in which a very fine suspension of the substance in water is diluted in a stepwise fashion; there is a sudden disappearance of the turbidity as soon as the aqueous solubility concentration range is reached. An instrument for micronising crystalline substances prior to the solubility determination has been designed. The method is simple and rapid and requires neither complicated apparatus nor analytical procedures. It is suitable for determining aqueous solubilities in the range from more than 1000 to less than 1 mg/litre. As a visual method, it would seem a priori to be less accurate than the “analytical” procedures recently described in the literature. When the solubility values given by different workers for the same substance are compared, however, discrepancies of a factor up to 10 are occasionally found. The accuracy obtainable with this new method readily suffices for the objective in view, namely to investigate to what extent the aqueous solubility of pesticide chemicals affects their behaviour during and after application. The aqueous solubilities of 34 commercial pesticide chemicals are tabulated; only in a few cases do the values obtained by the dilution method differ widely from those given in the 4th edition of the Pesticide Manual.