Objective:

This work presents the definition of uncertainties for the methods of analysis of aflatoxins B1, B2, G1 and G2 in raisins by HPLC-FLD. The uncertainty of a method is one of the parameters required by the norm IRAM 301-ISO/IEC 17025:2005Standard, applicable in the Argentine Republic and accredited by the Argentine Accreditation Organism (OAA), and forms part of the validation of analytical methods. In addition, it is a necessary requirement to expand the scope of accreditation of the Laboratory of Analysis of Regional Products of Chemical Engineering (LAPRIQ, by the name in Spanish), belonging to the Institute of Chemical Engineering of the National University of San Juan.

Methodology:

The procedure used is called “Bottom up”, based on a succession of calculation that take into account errors from each of the analytical operations decomposed in primary activities. For the initial stage, sources of error that can affect the result of the analysis were identified. The Ishikawa's fishbone procedure was used as a basis for determining the sources of error and their incidence in the final uncertainty of the process. Once the factors that add up to the error in the measurement were defined, all the HPLC calibration tests were performed. Second, the combined uncertainties were added, weighted according to the importance of their contribution through the sensitivity coefficient. Finally, the expanded uncertainty was determined using a coverage factor K = 2, which implies a confidence percentage of 95%. With this factor we can expect to include the largest fraction of the distribution of the values attributed to the measurand.

Results:

Six sources of error were detected and correspond, on the one hand, to the mass measurements of the sample, extraction volumes, elution, and aliquot for “clean up” and, on the other, HPLC detection and recovery rate of the method. The calculated uncertainties for the four aflatoxins are AFB1= 0.7 mg/kg, AFB2= 0.2 mg/kg, AFG1 = 0.9 mg/kg y AFG2 = 0.3 mg/kg.

Conclusions:

The values of the expanded uncertainties are reported in the certificate of analysis, along with the result of the HPLC test, as one of the tests of the validation of the method validation.