Evaluation of dry ashing in conjunction with ion chromatographic determination of transition metal ions in pig feed samples

The contents of transition metal ions iron, copper, zinc, and manganese were simultaneously determined in pig feed using an ion chromatographic technique (IC) preceded by dry ashing. Employing ion exchange, the ions were separated on an IonPac CS5A column used in combination with a pyridine-2,6-dicarboxylic acid based eluent. The separation was followed by spectrophotometric detection after postcolumn reaction with 4-(2-pyridylazo)resorcinol. Dry ashing parameters were varied to assess their role in potential analyte loss. Quantitative recoveries (>95%) were obtained for all analytes with a dry ashing method that included a moderate temperature-time regime and ash leaching support in the form of sonication and heat treatment. The use of HCl as leaching acid and the presence of alkaline earths in the matrix solution did not interfere with the chromatographic separation.