The researchers developed a method to measure nitrate and nitrite levels in canned and frozen foods using ion chromatography. They used a specific column and solution for separation and detection. The method showed a good linear relationship for nitrate and nitrite, with low variability in the results. The spike recovery rate in samples was close to 100%, indicating the method's accuracy. Overall, the method is suitable for analyzing nitrate and nitrite in various foods like spinach and carrots, with satisfactory results.