Longitudinal distribution of thallium in human scalp hair determined by isotope dilution electrothermal vaporization inductively coupled plasma mass spectrometry

A method for the direct determination of the longitudinal distribution of thallium in human scalp hair using isotope dilution electrothermal vaporization inductively coupled plasma mass spectrometry (ID-ETV-ICP- MS) was developed. Cleaning of hair is considered to be a critical step and of major importance with respect to the analytical procedure and results from analyses of unwashed and washed hair, using different washing procedures, were therefore compared. Small hair samples are difficult to handle and several methods to ease handling and introduction into the ETV were examined. Embedding hair strands in pressure-hardening glue before cutting them into 10 mm segments and injecting them with a solid sample injector proved to be the most successful. Several longitudinal concentration gradients were obtained of hair from a thallium-poisoned person. The thallium level in the root segment of the hair was about 0.4 mug g(-1), which is several orders of magnitude larger than the concentration normally found in hair. The concentration level then dropped to about 0.01 mug g(-1) close to the end of the 20 cm long hair strands analysed. The concentration of thallium in hair from non-exposed persons was found to be below the limit of detection for the method, i.e. 0.7 pg absolute amount, corresponding to about 5 ng g(-1) in dried hair using approximately 150 mg of sample for analysis.