Quantification of nitrate in simulated high-level liquid waste by Raman spectroscopy

A rapid analysis technique for determining nitrate in simulated high-level radioactive liquid waste (HLLW) was investigated using Raman spectroscopy. The concentration of nitrate can be quantified by the sharp and strong Raman peak height at 1047 cm^-1 and peak area in the range of 1020-1070 cm^-1 from the spectrum. The maximum Raman peak intensity and peak area of water in the range of 3000-3700 cm^-1 were chosen as the internal standards. The relative intensity I_nitrate/I_water showed good linearity with the concentration of nitrate at the range of 0.10-1.80 mol L^-1, and the fitted curve was y = 0.686x + 0.027 with a linear coefficient of 0.999. Another calibration curve between relative peak area A_nitrate/A_water and the concentration of nitrate, y = 0.0217x - 0.00036 in the range of 0.21-4.34 mol L^-1 was established, and the linear correlation coefficient was 0.999. Sulfate, phosphate, Zr, Cs, Nd and other ions demonstrated negligible interference on the nitrate determination. The presented method has been successfully applied to determinate nitrate in simulated HLLW samples with good recoveries at laboratory.