Determination of nitrate and nitrite in milk products by on-line dialysis and cadmium reduction flow injection analysis

Using on-line dialysis and cadmium reduction flow injection analysis method to determine nitrate and nitrite in milk products.A test portion was mixed with a warm extraction ammonium buffer solution.Fat was separated by centrifuging and rapid cooling.on-line dialysis was used to remove protein and remaining fat.The method was based on absorbance measurement of azo dye obtained by the reaction of nitrite with N-(1 naphthyl) ethylenediamine dihydrochloride and sulfanilamide.Nitrate was reduced to nitrite in a copperized cadmium column to obtain the concentration of nitrite plus nitrate.Linear calibration curves was obtained for the concentration range was 20.0～2000.0 μg/L N(r≥0.999) for both of nitrate and nitrite.The proposed method had low detection limit of nitrate was 4.4 μg/L N and of nitrite was 2.3 μg/L N.The relative standard deviation was 2.0%～5.8% and 0.2%～3.5% with the sample throughput of was 40 samples/h and 60 samples/h for nitrate and nitrite respectively.Nitrate and nitrite were determined in the real samples of various milk products with the recovery of nitrate was 94%～101% and of nitrate was 91%～107%.The method was simple,rapid and has been used to the determination of nitrate and nitrite in milk products with satisfactory results.