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) and salicylfluorone (SAF) to form anionic chelate and the collection of the ternary ion-associate of the chelate with tetradecylpyridinium chloride (TDPC) (a cationic surfactant) on an organic solvent-soluble membrane filter, of mu g l(-1)-level chromium(VI) ion in water has been described. 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 sulphuric acid, The absorbance of the resulting solution is measured at 515 nm against a reagent blank; the apparent molar absorptivity is 5.12 x 10(4) l mol(-1) cm(-1) at this wavelength. The completeness of the separation can be determined by means of the spectrophotometric method. Beer's law is obeyed in the range 0.4-1.4 mu g Cr(VI) in 5 mi of solvent 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 components normally present in natural water do not interfere. The proposed method has been applied to the separation and determination of chromium(VI) in water samples from several sources, the recoveries of the chrominm(VI) added to the samples are quantitative, and the results found are satisfactory.