EURL-FA Control Proficiency test report: Determination of authorised coccidiostats in compound feed

The European Union Reference Laboratory for Feed Additives (EURL-FA), hosted by the Joint Research Centre (JRC), a Directorate General of the European Commission, has been mandated by the Directorate General for Health and Food Safety (DG SANTE) to organise a proficiency test (PT) among appointed National Reference Laboratories (NRLs) in the frame of its control activities (according to the Regulation (EC) No 882/2004 [1]). The aim of this PT was to assess the capacity of the NRLs to correctly determine selected authorised coccidiostats added to feed matrices at realistic authorised levels and at cross-contamination levels. Thirty-six European National and Official Control laboratories were invited and twenty-nine laboratories registered to the 2017 PT exercise. Twenty-five of the registered laboratories reported results for the analyses. The test items used in this exercise were produced by the JRC. Purchased commercial poultry compound feed, tested by the EURL-FA Control as being blank for the target analytes, was milled and ground and then spiked with the required coccidiostat standard solution or with the relevant authorised feed additive. The first item was spiked with a standard solution containing monensin, narasin and diclazuril, at cross-contamination level (MAT 1). The second test item (MAT 2) was spiked with an authorised feed additive Maxiban®, containing narasin (narasin AL) and nicarbazin, at additive level. MAT 1 and MAT 2 were subsequently homogenised and distributed in glass bottles. All bottles were labelled ensuring a random number encoding and dispatched to all registered participants on 27 June 2017. Laboratories were informed of the composition of the test material regarding the composition in coccidiostats for MAT 2 and had therefore only to quantify the content. For MAT 1 the laboratories had to screen for the presence of all 11 authorised coccidiostats and to quantify the detected ones. The assigned values (xpt) for the mass content of monensin, diclazuril and narasin in MAT 1 were calculated from the formulation as recommended by the IUPAC harmonized protocol [2]. The uncertainties for the assigned values (u(xpt)) were calculated according to the ISO Guide for the Expression of Uncertainty in Measurement (GUM) [3]. For narasin and nicarbazin in MAT 2, no assigned value was set since the criterion for sufficient homogeneity could not be met. Participants were invited to report their measurement uncertainties. This was done by twenty-three out of twenty-five reporting participants for monensin and narasin, seventeen for diclazuril, and twenty for narasin AL and nicarbazin. Laboratory results were rated using z and ζ (zeta) scores in accordance with ISO 13528:2015 [4]. The relative standard deviation for proficiency assessment (σpt) for each assigned value was calculated using the relevant Horwitz [5] or modified Horwitz equation [6]. The z scores obtained were considered satisfactory if their absolute values were equal to or below 2. The outcome of this PT exercise is mixed; the percentage of satisfactory results reported by the laboratories for MAT 1 is 88%, 80% and 57% for monensin, narasin and diclazuril respectively. For narasin AL and nicarbazin in MAT 2, no scoring was computed but the data reported by the laboratories were examined. In general, there was good agreement among the values of mass content of narasin and nicarbazin reported results. The laboratories also reported qualitative results as regards the presence of one or more of the other authorised coccidiostats. On the whole, the rate of false positive results was of 4% for robenidine, lasalocid, salinomycin and maduramicin; 5% for nicarbazin; 8% for decoquinate; and 0% for all the others. Two laboratories did not quantify diclazuril in MAT 1 while stating a limit of quantification of the method used lower than the assigned value, leading to a false negative rate of 9% for this analyte. One laboratory could not quantify diclazuril in MAT 1 due to the lack of sensitivity of the method used.JRC.F.5-Food and Feed Complianc