Determination of nitrite and nitrate in dairy products by improved ion chromatography

Nitrite and nitrate are common inorganic salts in the diet and drinking water. It is generally believed that excessive intake of these substances may result in methemoglobinemia or other diseases. However, the traditional detection methods for nitrite and nitrate in dairy products restrain their applications to routine analysis due to the presence of certain limitations. In order to solve this problem, an improved national food safety standard method for the determination of nitrite and nitrate in dairy products has been studied. After water extraction, protein precipitation and centrifugation, the supernatant was cleaned up by a solid phase extraction (SPE) column. The eluent mainly composed of sodium hydroxide with acetonitrile as organic modifier. External water mode was used for suppressor. An AS 19 column was used as the analytical column, and the oven temperature was 30 degrees C while the cell temperature was 35 degrees C. The detection wavelength was 225 nm and the injection volume was 200 mu L. The results showed that good linearity existed when the concentrations of nitrite and nitrate were between 0.005 - 0.50 and 0.05 - 1.50 mg/L respectively. The detection limits of nitrite and nitrate were 0.2 and 0.04 mg/kg respectively when using a conductivity detector; while the values were only 0.02 and 0.01 mg/kg using an ultraviolet (UV) detector. The recoveries were between 84.0% and 104.1% when analyzing dairy products. It is a simple, fast and highly sensitive way for nitrite and nitrate detections.