DIRECT SPECTROPHOTOMETRIC DETERMINATION OF SULFATE IN NATURAL WATERS BY FORMATION OF FERRIC SULFATE COMPLEX

The method described here allows rapid determination of sulfate in the range of 10-500 mg/liter using the absorption of the FeSO4+ complex at optional wavelengths between 325 and 360 nm; it has been applied to the analysis of geothermal waters from drillholes in New Zealand and of brines from the Antarctic ice shelf. The method is accurate for solutions with negligible concentrations of phosphate, fluoride, ferric ion, and other interfering ions. It can therefore be applied to most natural waters. For determinations in chloride brines the approximate concentrations of NaCI or other major components, which change the activities of the ions involved in the formation of the FeSO4+ complex, have to be known and corrections have to be made. A diagram for the estimation of such correction factors is given for alkali, magnesium, and calcium chloride brines. The simplicity of the analytical procedure makes the method particularly useful when sulfate has to be determined in a large number of water samples of similar composition. © 1969, American Chemical Society. All rights reserved.