Determination of Nitrite and Nitrate in Milk Products by Ion Chromatography

An ion chromatography with conductivity detector (IC-CD) method was developed for the determination of nitrite and nitrate in milk products. Samples were dissolved in water and added with potassium ferrocyanide and zinc sulphate solutions for protein precipitation. The supernatant was cleaned up on C₁₈, Ag, and Na solid-phase extraction (SPE) columns, and analyzed by IC-CD. An external standard method was used for quantification. The IC-CD method was validated. Good linearity between the concentrations of nitrite (NaNO₂) and nitrate (NaNO₃) in the range of 0.01-0.20 mg/L and 0.1-2.0 mg/L, respectively and peak area was observed with correlation coefficient equal to or higher than 0.99. The limits of quantitation for nitrite and nitrate were 0.2 and 0.4 mg/kg, respectively. The spiked recoveries ranged from 92.5% to 102.0%, and the relative standard deviation (RSD) for precision from 1.5% to 6.6%. This method is accurate, repeatable, simple and applicable to the determination of nitrite and nitrate in milk products.