DEVELOPMENT OF INTERNAL FOREST SOIL REFERENCE SAMPLES AND TESTING OF DIGESTION METHODS

Our research requires determinations of total elemental concentrations of forest soils. The lack of certified forest soil reference material s led us to develop internal reference samples. Samples were collected from three soil horizons (Oa, B, and C) at three locations having for ested, acidic soils similar to those we commonly analyze. A shatterbox was used to homogenize the nine samples. The Radiation Laboratory of the University of Massachusetts, Lowell completed neutron activation a nalyses (NA) on our samples. Our laboratory performed five digestion p rocedures: microwave [nitric acid (HNO3), hydrochloric acid (HCl), flu oboric acid (HBF4), hydrogen peroxide (H2O2)], block [sulfuric acid (H 2SO4), selenious acid (H2SeO3), and H2O2], hot plate ([hydrofluoric ac id (HF) and perchloric acid (HClO4)], and flux [lithium berate (LiBO2) and lithium treborate (Li2B4O7)]. Concentrations of phosphorus (P), i ron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), sodium (Na), al uminum(Al), calcium(Ca), and potassium (K) were measured by direct cur rent plasma spectrometry (DCP). The results of the digestion procedure s were compared with results from the neutron activation analyses (NA) allowing us to choose the most effective digest procedure. Each diges tion procedure obtained varied elemental recovery rates (RR) ranging f rom Al with <10% RR for a C horizon sample digested in a block digesto r to Ca with >125% RR for a B horizon sample digested on a hot plate w hen compared to the neutron activation analyses values. Overall, the m aximum recovery rates were achieved by the flux, microwave, and hot pl ate procedures.