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|Title:||Investigations of the Feasibility of Producing a New "Natural" Matrix Reference Material for the Analysis of Pesticide Residues in Products of Plant Origin|
|Authors:||SALDANHA Helena Margarida|
|Abstract:||The specific objective of the work presented here is to study the feasibility of producing a Matrix Reference Material (carrot/potato based) for pesticide analysis. The material is intended as a quality assurance tool in support to european policies regarding pesticide residue legislation. This important component of quality control is not possible in the actual scenario since no natural matrix RM is available in the EU. However this approach, can be modified somewhat to account the unavailability of a natural matrix CRM to control the analytical procedure and validation of results: a validated method, with stated certainty. In this case the method replaces the absence of a CRM to asses the verification of the analytical process and spiking experiments are used to demonstrate the accuracy of the method. Isotope dilution mass spectrometry (IDMS) is regarded as such a method. A homogeneity study was carried out for the three candidate reference materials¿frozen, freeze-dried and sterilized carrot/potato matrices.Freezing and sterilization were intended to be an alternative to freeze-drying, where a reconstitution step is necessary, to ensure that the matrix format should be as similar as possible to routine laboratory samples. The main reason for the choice of these stabilization techniques is to improve the commutability between real-world samples and CRMs. Based on the method repeatability and the set-up of the study, in average the uncertainty contribution resulting from the homogeneity assessment is 6.1, 2.6 and 6.2 % respectively for the frozen, freeze-dried and sterilized batches of samples. In regard to the short stability studies designed for 4 weeks, stability of all 21 target analytes at -20 °C, in the frozen and dried matrices was proven by analytical measurements via GC-MS, along with the stability of the majority of the target pesticides at +4 °C (except phorate, lambda-cyhalotrin, permethrin and cypermethrin) in the dried matrix. This suggests that transport of such candidate reference material would be feasible at +4 °C for all target analytes, if phorate, lambda-cyhalotrin, permethrin and cypermethrin were not of interest, in a freeze-dried matrix.Moreover the determined average content (ng/g dry matter) is in agreement with the values obtained during homogeneity studies. The long-term stability studies enabled to select the best candidate materials. After conducting homogeneity/stability studies, frozen and freeze-dried materials were elected as the best option for the end-purpose and demonstrated the feasibility of producing a Matrix Reference Material for pesticides in carrots. All studied pesticides remained stable for a period of 5 months in the carrots matrix with an average combined uncertainty contribution of 8.2 % and 10.1 % in the frozen and freeze dried matrix respectively, to the exception of some late elucting compounds in the freeze dried-matrix. Thus, even if a laboratory would not be interested in (international) comparability of its measurements it would have to utilise references to avoid distortion of their measurements results.|
|JRC Institute:||Institute for Reference Materials and Measurements|
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