Comparison of sample decomposition procedures for the determination of zinc in milk by inductively coupled plasma atomic emission spectrometry

Abstract

Dry ashing and wet dissolution procedures for the decomposition of milk samples were compared based on zinc recovery and residual carbon content. Dry ashing of the samples at temperatures from 400 to 700 °C with and without additions of H₃BO₃, Mg(NO₃)₂ and H₂SO₄ was studied. Without an ashing aid zinc losses were observed at high temperatures, especially in the presence of chlorides. At a temperature of 500 °C zinc recovery was >95% and residual carbon content was 95%. The residual carbon varied and could be reduced through optimization of the digestion parameters (pressure, temperature and time) or by the addition of H₂SO₄ and/or H₂O₂ to HNO₃.