Cloud-point analysis of microlitre samples-determination of water in six common solvents

The classical cloud-point technique for determination of small amounts of water in organic solvents has been systematically investigated. The extreme sensitivity of the critical solution temperature of binary liquid mixtures to traces of impurity in one of the components makes the cloud-point method capable of high accuracy and sensitivity for routine determination of solvent contamination by water, and is admirably suited to analysis of small samples. Typically, the absolute error for water as contaminant is about 0.2% for 10-μl samples and 0.06 % for 50-μl samples. The critical solution temperature used was that of the n-hexane-methanol system. Its value is in dispute and considerable care was taken to obtain what is believed to be the correct value of 34,4 ± 0,2°. Small amounts of water in methanol, ethanol, 2-propanol, acetone, ethyl methyl ketone and dioxan were determined.