Dry- and wet-ashing techniques compared in analyses for zinc, copper, manganese, and iron in hair.

Preparation of hair specimens for trace-metal analyses is routinely done by wet- or dry-ashing. Wet-ashing is more time consuming than dry-ashing and can be dangerous. We wished to determine if dry-ashing was a suitable alternative to wet-ashing with HClO4:HNO3 or HNO3 alone in preparing hair for measurement of zinc, copper, iron, and manganese by atomic absorption spectroscopy. Concentrations of Zn, Cu, and Mn were not differently affected in hair that was dry- or wet-ashed. Analytical recovery of these elements added to hair samples ranged from 102 to 108%; day-to-day CVs were less than 5%. Fe was lost during dry-ashing of hair, and wet-ashing with HNO3 produced results for Fe comparable with those obtained with HClO4:HNO3. Therefore we recommend dry-ashing of hair to be analyzed for Zn, Cu, and Mn, but wet-ashing with HNO3 for assays of Fe.