Quantitation of sulfur oxyanions in industrial metal refining solutions with dispersive and fourier transform raman spectroscopy

Fourier transform (FT)-Raman and dispersive, visible excitation Raman spect ra are reported for standard solutions and highly colored industrial metal refining solutions containing sulfur oxyanions, primarily sulfate and sulfa mate. Good-quality spectra are obtained for both standard and industrial so lutions. However, quantitation of both sulfur oxyanion concentrations is co mplicated by self-absorption effects, In the FT-Raman spectra, self-absorpt ion of the incident laser beam yields an exponential correlation between Ra man peak intensity, directly proportional to the apparent sulfate concentra tion, and the actual sulfate concentration, An internal standard, dispersiv e Raman spectroscopy, and excitation at 647 nm were used in an attempt to a pply a self-absorption correction for absorption of the incident laser beam by ratioing the relative Raman intensities of the standard and species of interest. This approach improves the accuracy for sulfate and sulfamate det ermination to +/- 6.1% and +/- 3.4%, respectively. This study represents th e most detailed characterization presented so far of the errors expected in quantitative Raman spectroscopy of industrial solutions. These results sug gest that Raman spectroscopy is a uniquely powerful technique for the quali tative and quantitative characterization of industrial metal refining solut ions.