QUALITY-CONTROL IN HAIR ANALYSIS - A SYSTEMATIC STUDY ON WASHING PROCEDURES FOR TRACE-ELEMENT DETERMINATIONS

Trace element analysis of human hair is widely used to provide an indi cator of body burden, but there is a major problem associated with pre paration. The washing procedure adopted before analysis represents sti ll a critical point which deserves particular attention. This study ai med at comparing the efficiency of the most commonly used washing meth ods to identify the procedure which allows for satisfactory removal of external contamination alone. As results depend strongly on the eleme nt, toxic (Cd and Pb), essential trace (Cr, Cu, Se and Zn) and major ( Ca, K and Mg) elements were tested. The comparison was carried out wit h six different methods which include use of ionic and non-ionic deter gents, organic solvents, chelating agents and sonication. Removal effi ciency varied according to the element and pretreatment, the highest b eing observed for EDTA and the lowest for sonication. Unsatisfactory r esults were found using an acetone/methanol mixture for the potential contamination caused by it. Organic solvents showed the highest remova l efficiency for K and toxic elements, and seemed to be effective in r emoving a limited but significant fraction of element incorporated in the lipid matter of hair. The ionic detergent Na lauryl sulphate, inst ead, was more effective for essential elements, but also triggered a h igher analytic variability. As detergents appear to remove only extern al contamination, a non-ionic detergent such as Triton X-100 is propos ed as a reliable alternative to the acetone method recommended by IAEA . Practical advantages are safe working conditions, rapidity of applic ation and reduction in costs.