IC Determination of Nitrite and Nitrate in Milk Powder with Sampling by Membrane-Dialysis

IC was applied to the determination of nitrite and nitrate in milk powder with sampling by membrane-dialysis. The sample solution was dialyzed with molecular weight cutoff of 3.5 to 5 kD membrane, and the dialysate was filtrated through 0.22 μm filtering membrane. The filter was eluted with KOH solutions of various concentrations. Contents of NO2- and NO3- in the elutes were determined separately by UV-detections at the wavelength of 210 nm. Linearity ranges of NO2- and NO3- found were between 0.02-0.5 mg·L-1, 0.2-5.0 mg·L-1 with detection limits (3S/N) of 0.01, 0.008 mg·L-1, respectively. In analyzing some substantial samples by this method, values of RSD′s for NO2- and NO3- (n=6) found were 2.7%, 1.9% respectively. Values of recovery found by standard addition method were in the range of 90.7%-105%.