Development of a reference material for residues of chlorfluazuron and fluazuron in beef fat ACSL CRM 3

The certification by interlaboratory testing of a candidate reference material (ACSL CRM 3) for the concentration (mass fraction) of the pesticides chlorfluazuron (CFZ) and fluazuron (FZN) is described. The certification process was based on a two-stage nested design described in ISO Guide 35. Analysis of results reported by collaborating laboratories provided an assessment of the homogeneity of the RM. The certified values were chlorfluazuron -1.01 mg/kg and fluazuron -1.02 mg/kg. The upper and lower 95% confidence limits for CFZ and FZN were calculated to be: CFZ upper=1.05 mg/kg, lower=0.97 mg/kg; FZN upper=1.08 mg/kg, lower=0.95 mg/kg. A certificate was prepared according to guidelines set out in ISO Guide 31.