EFFECT OF THE WATER SPECTRUM ON THE DETERMINATION OF DISSOLVED AMMONIA, UREA, AND CHLORIDE CONCENTRATIONS BY RAMAN-SPECTROSCOPY

The effect of large, changing concentrations of electrolytes on the be havior of the OH stretching band of water have been investigated with the aim of developing methods for compensating for spectral interferen ces when solute NH bands are made the basis for mixture analyses. With the use of urea and ammonium salts as analytes, it was found that cha nging electrolyte concentrations affect the shape of the water band bu t do not appreciably affect the shapes of either the ammonium ion or u rea Raman lines. Chlorides, nitrates, and mixtures of these were used as electrolytes. The identity of the anion had a significant effect on the shape of the OH band. Two methods of compensation were used. One involved factor analyzing the spectra of a set of solutions that conta ined chlorides and nitrates that are Raman inactive in the vicinity of the OH stretching band. The principal abstract factors were used in p lace of a water reference for a least-squares mixture analysis. The ot her method was application of partial least-squares. In addition to ur ea and ammonium ion, the concentration of KCl and the ionic strength o f the system can be determined in the partial least-squares approach w ith limits of detection better than 0.1 M.