Bovine blood lead reference material

A protocol is described for the preparation and characterization of bovine blood lead (Pb) reference material (RM). Adult bovine animals are orally dosed with Pb as Pb(NO3)2, and blood is collected directly from the jugular vein into 5-mL evacuated, low-Pb glass tubes containing EDTA as anticoagulant. The blood is cooled to 4 degrees C for 24 h and frozen and stored at -20 degrees C. Over 400 RMs were prepared and certified for reference values (RV) since the inception in 1974 of the Childhood Blood Lead Proficiency Testing Program. Five reference laboratories employing blood Pb methods of various principles were used to certify the RV, representing the true value, of 5 representative RMs containing 6.4-54.0 micrograms Pb/mL. Intertube homogeneity was verified by reference laboratories determining blood Pb in 20 tubes of 150 tubes collected from each of the 5 representative RMs. Intratube homogeneity was verified by an internal laboratory determining Pb in 12 consecutive 10-microL samples from 5 mL of blood in each of 3 representative RMs. Pb was unchanged in 37 bovine blood Pb RMs containing EDTA as anticoagulant after storage at -20 degrees C for 32-48 months.