A Comparative Study of Plant Sample Preparation by Dry Ashing and Wet Digestion for Isotopic Determination of Cu, Zn and Fe
干法灰化和湿法消解植物样品的铜锌铁同位素测定对比研究

Dry ashing and wet digestion are common methods for determining the content and isotopic composition of elements in organic samples. Wet digestion has been used mostly to dissolved samples for determining Cu, Zn and Fe isotopes. Relative to wet digestion, dry ashing is not only more efficient in sample preparation, but also uses less acid, thus suitable for bulk treatment. However, under high temperature, it is possible to cause isotope fractionation of Cu, Zn and Fe during sample processing because of evaporation. A comparative study of elsholtzia splendens samples prepared by using dry ashing and wet digestion was carried out. The results show that: 1) for the elsholtzia splendens roots, the process of dry ashing does not cause isotope fractionation of Cu, Zn and Fe; 2) for elsholtzia splendens stems, the process of dry ashing does cause isotope fractionation of Fe, but no fractionation of Cu and Zn isotopes occurs; 3) for the elsholtzia splendens leaves, the process of dry ashing does cause isotope fractionation of Cu and Fe, but no fractionation of Zn isotopes occurs. In a word, the suitability of the dry ashing method for plant sample digestion needs to be evaluated specifically according to the features of the sample and the element studied. The loss of the elements in volatile components is a main cause leading to different fractionation effects of Cu, Zn and Fe, as in dissolving the organic samples by using dry ashing process. Both of the two factors, i.e., the isotopic difference between volatile components and the whole sample and the relative variation of the elements, result in different isotopic fractionation effects in the process of volatilization.