The use of reference materials in the elemental analysis of biological samples.

Reference materials (RMs) are useful to compare the accuracy and precision of laboratories and techniques. The desirable properties of biological reference materials are listed, and the problems of production, homogenization and storage described. At present there are only 10 biological RMs available compared with 213 geological and 520 metallurgical RMs. There is a need for more biological RMs including special materials for microprobe analysis and for in vivo activation analysis. A study of 650 mean values for elements in RM Kale, analysed by many laboratories, leads to the following conclusions. 61% of the values lie within +/- 10% of the best mean, and 80% lie within +/- 20% of the best mean. Atomic absorption spectrometry gives results that are 5-30% high for seven elements, while instrumental neutron activation analysis gives low and imprecise results for K. Other techniques with poor interlaboratory precision include neutron activation for Mg, polarography for Zn and arc-spectrometry for many elements. More than half the values for elements in Kale were obtained by neutron activation, confirming the importance of this technique and the need for RMs. As a rough estimate, 6 X 10(9) elemental analyses of biological materials are carried out each year, mostly by medical, agricultural and food scientists. It seems likely that a substantial percentage of these are inaccurate, a situation that might be improved by quality control using standard RMs.