Ma. Wilson et al., TOTAL ELEMENTAL ANALYSIS DIGESTION METHOD EVALUATION ON SOILS AND CLAYS, Communications in soil science and plant analysis, 28(6-8), 1997, pp. 407-426
The standard digestion method for total elemental analysis of soil mat
erial by the Soil Survey Laboratory (USDA Natural Resources Conservati
on Service) uses a 2-mL clay suspension with hydrofluoric acid (HF) in
a closed Teflon digestion vessel (method HF-SUS). The accuracy and ef
ficiency of elemental recovery by method HF-SUS was compared to: (a) m
odification of HF-SUS by use of a dried sample (method HF-DRI); (b) mo
dification of HF-SUS by use of a dried sample and HF+aqua regia (metho
d HF+AR); (c) sample digestion by Li metaborate fusion (method FUS); a
nd (d) microwave digestion of samples with HF+aqua regia in Teflon bom
bs (method MICRO). Three replications of three standard reference mate
rials (SRMs), fine-earth (<2 mm) from 12 soils, and the clay (<2 mu m)
from 10 of those soils were analyzed. Method HF+AR shows the most con
sistent statistical agreement with the certified SRM values. Analysis
of variance (ANOVA) indicates significant effects (alpha=0.05) for met
hod of digestion, nonsignificant effects for method times SRM and meth
od times clay, but significant effects for method times fine-earth. Co
mposition and/or variability of material are significant factors in th
e method of digestion. Method HF+AR yields significantly higher experi
mental means of Al2O3, Fe2O3, and K2O contents and oxide recovery (sum
mation of experimental means for oxides of all reported elements) than
all other methods.