Evaluation of an HPIC Method for Determination of Nitrates in Vegetables

The aim of the work was to verify the reliability of an HPIC method for determination of nitrates in vegetables using statistical analysis to evaluate validation parameters according the ISO/IEC 17025:2005. Standard solutions were used for the construction of a calibration curve, which was supported by Varian Star Workstation software. All calculated validation characteristics were summarized in an Excel table with final evaluation of the method. Repeatability was characterized by the selected variation coefficient sR, calculated from the standard deviation sd and arithmetic mean from a series of measurements under repeat conditions, accuracy by the variation coefficient sR, and recovery. The repeatability of the method of 3.62% is under the set limit of 5%. The calculated uncertainty was 4.22% with a recovery of 99.2%. Determination of nitrate was linear over the whole range of the calibration graph. The LOQ was 0.60 mg L−1, which is fully acceptable within the requirements for nitrate determination in plant materials. Standard uncertainty of these methods was calculated as an expanded uncertainty according to Eurachem documents in the PC program Metro2003, version 2.30.