Interlaboratory study of trace elements in keratinized matrices: characterization of four caprine horn reference materials and an investigation of current analytical methodologies

Abstract

Keratinized tissues comprise a diverse family of materials that includes hair, nails, horns, and hooves. Because of their convenience for collection, affinity for binding some trace elements, and the potential to provide information about historical exposure, hair and nails have been used to assess population exposure to toxic metals and metalloids. Previous studies, however, report a lack of harmonization and poor reliability among commercial laboratories performing trace element analysis of hair. In this interlaboratory study, four keratinized reference materials (RMs) were produced from caprine horns obtained post-mortem from Pb-dosed goats. The homogenized RMs were circulated to laboratories that conduct trace element analysis of keratinized tissues to assess interlaboratory harmonization. Sources of variability in the analytical methods used by participants were investigated. Results were obtained from 21 participant laboratories for a total of 44 elements. Good interlaboratory agreement was found for the majority of elements typically measured using ICP-MS following acid digestion. However, for Al, Cr, Hg, Mo, Ni and V, there was a poor consensus, caused in part by differences in correcting for spectral interferences. Measurements for Hg were inconsistent, which suggests a need for increased efforts to achieve better harmonization. Sample mass for acid digestion was negatively correlated (p = 0.02) with reported Pb content. Higher digestion temperatures were correlated with increased Mn recovery. A limited quantity of four well-characterized caprine horn RMs were produced as a result of this study and serve as a resource for future harmonization efforts.