Differential pulse polarographic determination of nitrate and nitrite in nuclear wastes

Solid particles for nuclear fuel fabrication can be produced by gel-supported precipitation. Process by-products are aqueous wastes containing organic materials, ammonium nitrate and ammonia that can be decomposed into nitrogen compounds. A differential pulse polarographic determination of nitrate- and nitrite-nitrogen in such mixtures is described. The proposed method is based on the previous separation of nitrate and nitrite ions from inorganic and organic interferents. After ammonia volatilization, the separation is achieved with a column of Amberlite IRA 410 (Cl- form) anion exchange resin that is then eluted with 2.5M NaCl. An aliquot of the eluate is made 1M NaCl, 0.012M HCl and 0.0001M U(VI) and polarographic cumulative determination of nitrite and nitrate follows at - 0.93V (vs. Ag/AgCl) potential. Then a solution 6.5 x 10-5 in diphenylamine, 2.5 x 10-3M in sodium thiocyanate and 3 x 10-2M in perchloric acid is added to a second aliquot of the eluate and differential pulse polarographic determination of nitrite follows at -0.52V (vs. Ag/AgCl). The proposed method permits determinations of nitrite-nitrogen levels as low as 5 ng N ml-1 and of nitrate-nitrogen levels at 200 ng N ml-1. Relative standard deviations less than 4% may be routinely achieved. Analysis time is approximately one hour per sample. (Author)