Report on the 2015 proficiency test of the European Union Reference Laboratory for Mycotoxins, for the Network of National Reference Laboratories : determination of cintrinin in red yeast rice

The Institute for Reference Materials and Measurements (IRMM) of the Joint Research Centre (JRC), a Directorate-General of the European Commission, operates the European Union Reference Laboratory (EURL) for Mycotoxins. One of its core tasks is to organise proficiency tests (PTs) among appointed National Reference Laboratories (NRLs). This report presents the results of the PT on the determination of citrinin in red yeast rice samples. The test items were two naturally contaminated samples (Sample A and B). The materials were obtained from CODA-CERVA (Tervuren, Belgium). Samples were processed (milled, homogenized and packed) by the IRMM and dispatched to the participants in July 2015. Each participant received two amber containers filled with approximately 20 g per test material. The analysis of Sample B, which contained a level of citrinin in a region relevant for food law enforcement in the EU, was mandatory, while the determination of citrinin in sample A was optional, as it was intended to assess the measurement capability near the region of the estimated LOQ for many methods in use. Thirty-six participants from twenty-nine countries registered for the exercise and thirtythree sets of results were reported. The assigned values, established by exact-matching double isotope dilution mass spectrometry at the EURL for Mycotoxins, were 13.8 μg/kg (Sample A) and 1142 μg/kg (Sample B) for citrinin. The expanded uncertainties of the respective assigned values were 2.1 and 46 μg/kg. Participants were invited to report the uncertainty of their measurements. This was done by the majority of laboratories. Laboratory results were rated with z-scores and zeta-scores in accordance with ISO 13528:2005 and the IUPAC International Harmonized Protocol for the Proficiency Testing of Analytical Chemistry Laboratories. The z-score compares the participant's deviation from the reference value with the target standard deviation accepted for the proficiency test, whereas the zeta-score provides an indication of whether the participant's estimate of uncertainty is consistent with the observed deviation from the assigned value. Only z-scores were used for the evaluation of performance. In total 47% of the attributed z-scores were below an absolute value of two, which showed that only half of the participants performed satisfactorily. The evaluation of results suggests a strong correlation between underperformance and the nature and quality of the reference standard used for calibration. Another source for unsatisfactory results may be the amount and composition of extraction solvents used by the participants. However, as the distribution of testing results reported by the participants is skewed to the right (i.e. a significant number of participants overestimated the citrinin content) a calibrant whose nominal concentration deviated from the true value was the most likely cause.