Determination of Submicrogram Amounts of Inorganic and Organo-Mercury Compounds by Absorption Spectrophotometry

Abstract

A method for the speciation of inorganic, phenyl and methyl mercury(II) species by spectrophotometry has been developed. Selectivity was achieved by extracting off phenyl and methyl mercury(II) species into benzene and volatilising the inorganic mercury(II) species using stannous chloride for reduction to elemental state. Methylmercury and phenyl mercury(II) were selectively stripped by equilibration with NaOH and EDTA, respectively. The separated species were transformed to mercury paraperiodate by treatment with acidified periodate solution. After masking the unreacted periodate with molybdate, each atom of mercury were made to release 33.2 atoms of iodine through a sequence of reactions. The liberated iodine was transformed to ICl₂ ⁻ species by reaction with iodate in the presence of chloride and acid and extracted as ion-pair with rhodamine 6G for spectrophotometric measurement at 535 nm. The method has been applied to natural waters, chloralkali plant effluent, hydrogen gas and biological samples.