Proficiency testing to evaluate the effectiveness of laboratories analyzing active ingredient in formulation samples

This paper describes the organization and evaluation of the proficiency tests (PTs) organized by the Italian National Institute of Health (ISS) during 2018 and 2019. The aim of the PTs was to determine the quantity of active ingredient in various formulations of plant protection products (PPPs). In 2018, the Italian National Institute of Health (ISS) had organized PTs for the determination of Cymoxanyl, Oxamyl, and Methomyl in three different plant protection product (PPP) formulations. This is the first PT in Italy that uses a commercially available plant protection product in a different formulation, such as a wettable powder (WP), granule (GR), and soluble liquid (SL). In 2019, the ISS organized proficiency testing for the determination of Amisulbron, Dimethomorph, Pirimiphos-methyl, and Propiconazole in four different formulations of PPPs. For this proficiency testing, the commercial PPPs was obtained from the market in the formulation, as wettable dispersible granules (WDG), wettable powder (WP), liquid (L), or emulsifiable concentrate (EC). In 2018, all laboratories obtained data with acceptable values of z-score within limits, except for three of them that returned z-score values higher than 3.5 for the active substances Cymoxanil and Methomyl. In 2019, all laboratories obtained data with acceptable values of z-score within limits, except for three laboratories that returned z-score values higher than 3.5 for the active substances. The performance of the laboratories expressed in terms of modified z-score was satisfactory by almost all participants for all substances.