A comparison of washing methods for hair mineral analysis: internal versus external effects

A major difficulty in hair elemental (mineral) analysis for biomonitoring is adequate understanding of the effectiveness of washing procedures. A review of washing protocols used in hair analysis publications showed little consensus with regard to solvents and surfactants used, washing times, and number of washing stages. Two washing approaches were subsequently used to compare their influence on internal and external surface elemental signals determined with time-of-flight secondary ion mass spectrometry. Na, K, Ca, Mg, and Fe were assessed with regard to their relative signal compared to carbon. Both washing methods had similar effect. All elements except for Fe appear to be removed from the surface of the hair as well as from inside the hair. Only the internal Fe content changed with washing and could indicate that external surface bound Fe may not be removed with most washing procedures. It is shown that washing procedures can have a significant effect on reducing the internal elemental signal levels in hair.