EXTRACTION-SPECTROPHOTOMETRIC DETERMINATION OF MERCURY(II) USING THIACROWN ETHERS AND BROMOCRESOL-GREEN

A reasonably sensitive and highly selective spectrophotometric method for the determination of mercury(II) is proposed. The method is based on the extraction of the ion-associate formed by a mercury(II) thiacro wn ether cationic complex with Bromocresol Green as the anionic counte r-ion using chloroform as the extracting solvent. The effect of thiacr own ethers of different cavity sizes, namely 1,4,7,10,13-pentathiacycl opentadecane (PTP) and 1,4,7,10,13,16-hexathiacyclooctadecane (HTO), t he thiacrown ether concentration, the extracting solvent, the bromocre sol green concentration and the aqueous phase pH on the extraction wer e investigated. Measurement of the absorbance at the lambda(max) (420 nm) of the extracted ion-associate reveals that Beer's law is obeyed o ver 0.5-12.0 ppm mercury(II) for both ligands. Slight interference fro m copper(II) and cadmium(II) is exhibited by the PTP ligand, while HTO is negligibly affected by these metal ions. Strong interference from silver(I) is evident for both ligands while alkali, alkaline earth and other transition metals tested posed negligible interference. Analysi s of mercury in synthetic complex mixtures was satisfactory