COMPARISON OF DIFFERENT WASHING, ASHING, AND DIGESTION METHODS FOR THE ANALYSIS OF TRACE ELEMENTS IN VEGETATION

Quantitative determination of the concentration of trace elements in vegetation is important in studies dealing with
environmental impact, nutrition effects and geochemical exploration. However, the great diversity of sample
preparation and analytical methods involved in the determination of trace elements in plant material makes the
inter-comparison of the results reported in scicntific literature difficult. The objective of this investigation was to
compare the effects of different sample preparation, particularly cleaning, drying and digestion, used prior to the
determination of the concentrations of ten trace elements (As, Cd, Co, Cr, Cu, Fe, Mn. Ni, Pb and Zn) in plant
material. The results of the investigation suggested that the best cleaning method in studies of multielement
concentrations in vegetation is washing collected plant samples thoroughly with distilled water. Ashing at 550°C
followed by digestion with a mixture of HN@:H2S04 (2: 1) appeared to be the best method for drying and digestion
of the plant material. However, modifications of this technique can considerably improve the recoveries for some
elements, such as arsenic and chromium.

INTRODUCTION
The interest in determining the concentrations of trace elements in vegetation goes back to
the beginning of the nineteenth century . Up to the 1920 s quantitative determination of
concentrations of trace elements was carried out by colorimetric and volumetric methods,
with detection limits in the upper mg.kg- level. Fast improvements in analytical techniques
during the last decades enabled scientists to determine trace elements in plant samples at the
pg.kg- and n9kg-I levels. However, less effort has been devoted to the optimization of the
sample preparation.
A large diversity of methods for preparation of vegetation samples reported in recent
literature (Table 1) makes comparison of results from different studies difficult. The
diversity of the sample preparation begins with the selection of the plant organs for analysis.