L-shell x-ray fluorescence measurements of lead in bone: accuracy and precision.

This study aimed to quantify the accuracy and precision of a method for in vivo measurements of lead in bone using L-shell x-ray fluorescence (LXRF), the former via comparison with independent measurements of lead in bone obtained using electrothermal atomic absorption spectrometry (AAS) following acid digestion. Using LXRF. the lead content of adult human cadaver tibiae was measured, both as intact legs and as dissected tibiae with overlying tissue removed, the latter at several proximal-distal locations. After LXRF, each tibia was divided into nine cross-sectional segments, which were further separated into tibia core and surface samples for AAS measurement. The proximal-distal variability of AAS-measured core and surface tibia lead concentrations has been described elsewhere (the lead concentration was found to decrease towards both ends of the tibia). The subjects of this paper are the proximal-distal variability of the LXRF-measured lead concentrations, the measurement uncertainty and the statistical agreement between LXRF and AAS. There was no clear proximal-distal variability in the LXRF-measured concentrations; the degree of variability in actual tibia lead concentrations is far less than the LXRF measurement uncertainty. Measurement uncertainty was dominated by counting statistics and exceeded the estimate of lead concentration in most cases. The agreement between LXRF and AAS was reasonably good for bare bone measurements but poor for intact leg measurements. The variability of the LXRF measurements was large enough, for both bare bone and intact leg measurements, to yield grave concerns about the analytical use of the technique in vivo.