Measurements for certification of chlortetracycline reference materials within the European Union Standards, Measurements and Testing programme

The experimental design of a material certification programme is described. The matrix reference materials (RMs) comprised chlortetracycline (CTC)-con taining and CTC-free lyophilised porcine liver, kidney and muscle produced under the European Commission's Standards Measurements and Testing (SMT) pr ogramme. The aim of the certification programme was to determine accurately and precisely the concentration of CTC and 4-epi-chlortetracycline (epi-CT C) contained in the RMs. A multi-laboratory approach was used to certify an alyte concentrations. Participants (n = 19) were instructed to strictly adh ere to previously established guidelines. Following the examination of anal ytical performance criteria, statistical manipulation of results submitted by 13 laboratories, (6 withdrew) allowed an estimate to be made of the true value of the analyte content. The Nalimov test was used for detection of o utlying results. The Cochran and Bartlett tests were employed for testing t he homogeneity of variances. The normality of results distribution was test ed according to the Kolmogorov-Smimov-Lilliefors test. One-way analysis of variance (ANOVA) was employed to calculate the within and between-laborator y standard deviations, the overall mean and confidence interval for the CTC and epi-CTC content of each of the RMs. Certified Values were within or ve ry close to the target concentration ranges specified in the SMT contract. These studies have demonstrated the successful production and certification of CTC-containing and CTC-free porcine RMs.