Modification of the ion exchange HPLC procedure for the detection of nitrate and nitrite in dairy products

Existing ion exchange HPLC methodology for nitrate and nitrite analysis in cured meat products suffers from high analyte variability at low concentrations and also chromatographic interference by artifacts in some other foods, such as dairy products. An investigation into the sources of variability has shown that both the cyclohexyl solid phase extraction cartridge and the glass fibre filter used in the original method can introduce artifacts which interfere with the determination of the nitrate in foodstuffs. We have also found that the use of a graphitized solid phase extraction cartridge used in tandem with the cyclohexyl solid phase extraction cartridge removed the artifacts from the chromatograph of dairy products that co-eluted with nitrite and nitrate. Values for the nitrite and nitrate content of dairy products were obtained by the HPLC procedure using these two solid phase extraction cartridges and the values obtained were in close agreement with those obtained by cadmium column reduction and colorimetry.