Production of CTC-containing porcine reference materials

The European Commission (EC) established the Standards, Measurements and Te sting programme for the preparation of Reference Materials (RMs) as an aid to harmonise testing for veterinary drug residues throughout the European U nion (EU). The production of chlortetracycline (CTC)-free and CTC-incurred pig tissues as candidate RMs is described. High performance liquid chromato graphy (HPLC) with fluorescence detection of CTC and 4-epi-CTC was used for all tissue analyses. A pilot study revealed that incurred CTC residues wer e stable in pig kidney, liver and muscle lyophilised powders during storage for 10 weeks at -70, -20 and +37 degrees C, obviating the need for additio n of a stabiliser (thimerosal). In the main study, 500 vials each of CTC-fr ee and CTC-incurred kidney, liver and muscle were produced. Target concentr ations in the CTC-incurred lyophilised tissue powders were 750-1500, 500-10 00 and 300-600 mu g kg-l for kidney, liver and muscle, respectively. Follow ing lyophilisation, the mean +/- s concentrations of CTC in the incurred po sitive RMs were 1315 +/- 56.9, 765 +/- 35.3 and 378 +/- 16.8 mu g kg(-1) fo r kidney, liver and muscle respectively. Residual moisture in the RMs range d from 1.6 +/- 0.53% for muscle to 3.0 +/- 0.50% for liver. Between-vial ho mogeneity for incurred powders was determined for 20 vials of each material , which had been removed at regular intervals during the filling process. R elative standard deviations (RSDs) for kidney, liver and muscle were 4.3, 4 .6 and 4.4% respectively, being within the interassay RSD of the method and indicating that mixing was effective. Stability of powders stored at -18, 4, 20 and 37 degrees C was assessed over a period of 79 weeks. No measurabl e degradation occurred over this time period at any of the storage temperat ures. It is concluded that these candidate RMs are homogenous, stable and a re suitable for certification.