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Accreditation of the analytical method used for nitrate determination in vegetables

Kmecl Veronika (Agricultural Institute of Slovenia, Ljubljana, Slovenia)
Žnidarčič Dragan (University of Ljubljana, Biotechnical Faculty, Department of Agronomy, Ljubljana, Slovenia)

The standard method of EN 12014-7 was used for the determination of nitrate content in vegetables in the Central Laboratory of the Agricultural Institute of Slovenia. Trueness of the method was verified by the analysis of samples in the interlaboratory proficiency testing scheme Bipea (Bureau Interprofessionnel d'Etudes Analytiques). Linearity was confirmed by multiple linear regression; the correlation coefficient (R2) was 0.9993. The limit of detection (LOD) was calculated as 0.8 mg NO3-/kg and limit of quantification (LOQ) 3.0 mg NO3-/kg. Relative standard deviation (RSD) of repeatability was 4.6% and RSD of reproducibility 8.9%. The relative uncertainty of repeatability and reproducibility were 10.5% and 20.2%, respectively. The method has been accredited by the French Accreditation Committee COFRAC in 2007 and by the national Slovene Accreditation in 2012.

Keywords: nitrates, validation, accreditation, continuous flow method