Determination of minor and trace elements in human hair - an interlaboratory comparison

Abstract

This article discusses the results of an interlaboratory comparison for the analysis of elemental concentration in human hair samples as an example of a human biological material. The analysis concerned the determination of the content of the following elements: P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Mo, Pb and Hg. Six laboratories from five countries (Poland, Germany, Spain, Portugal, and Croatia) participated in the interlaboratory comparison and performed the analyses using the following methods: TXRF (three laboratories), μ-EDXRF (one laboratory), ICP-OES (one laboratory), and ICP-MS (two laboratories). The statistical analysis of the results was performed separately for the TXRF measurements and also including the results obtained using other measurement techniques. The element concentrations obtained by TXRF cover wide range from about 0.2 mg/kg (Mn As Se Rb Sr Pb) to 37,000 mg/kg (S). Additionally, for the TXRF technique, the detection limits (from 0.1 mg/kg to 20–80 mg/kg (the lightest element P)) as well as the intra-day (from 0.2 % to 22 %) and inter-day (from 0.3 % to 19 %) precisions were estimated. For identification and rejection of outliers the Dixon's and the Grubbs' tests were applied. For the remaining results the consensus mean values and standard deviations of element concentrations were calculated. Next, these parameters were used to determine the z-scores for concentration of each element ranging in the interval − 2 ≤ z ≤ 2. In order to compare the dispersion of results, coefficients of variation were determined. It was shown, that the value of variation coefficient depends on the studied element and its concentration in the sample. The obtained results made it possible to estimate the reproducibility of elemental analysis of hair samples performed using various methods in a wide range of atomic numbers and element contents.