NEW SEPARATION METHOD FOR CHROMIUM(VI) IN WATER BY COLLECTION OF ITS TERNARY COMPLEX ON AN ORGANIC SOLVENT-SOLUBLE MEMBRANE-FILTER

A new separation method, based on the reaction between chromium(VI) an d salicylfluorone (SAF) to form anionic chelate and the collection of the ternary ion-associate of the chelate with tetradecylpyridinium chl oride (TDPC) (a cationic surfactant) on an organic solvent-soluble mem brane filter, of mu g l(-1)-level chromium(VI) ion in water has been d escribed. The ternary complex (Cr(VI):SAF:TDP=1:2:2), collected on a 0 .45 mu m nitrocellulose filter is dissolved with the filter in a small volume of 2-methoxyethanol(methylcellosolve) acidified with dilute su lphuric acid, The absorbance of the resulting solution is measured at 515 nm against a reagent blank; the apparent molar absorptivity is 5.1 2 x 10(4) l mol(-1) cm(-1) at this wavelength. The completeness of the separation can be determined by means of the spectrophotometric metho d. Beer's law is obeyed in the range 0.4-1.4 mu g Cr(VI) in 5 mi of so lvent with good reproducibility. Detection limits better than 1 mu g l (-1) of Cr(VI) can be achieved with a 20-fold enrichment factor. The c omponents normally present in natural water do not interfere. The prop osed method has been applied to the separation and determination of ch romium(VI) in water samples from several sources, the recoveries of th e chrominm(VI) added to the samples are quantitative, and the results found are satisfactory.