USING HPLC-ICPMS TO CHARATERIZE PATTERNS OF METAL SPECIATION IN SOILS

It is well known that soluble organic acids can greatly enhance mineral dissolution and metal transport during pedogenesis. The strength of the organo-metallic interactions influences both the removal of metals from the soil profile as well as their availability to plants and microbes. However, a clear understanding of the behavior of metals and soluble organic acids is limited for several reasons. First, published stability constants are considered conditional, as they are determined under laboratory conditions that may not extend to natural soil environments, making modeling these interactions in soil ineffective. Additionally, direct measurements are complicated by the interaction of separation methods with compounds of interest. We have developed an HPLC-ICPMS technique to separate small aliphatic and aromatic organic compounds that represent functional groups in natural humic substances and subsequently measure the metals associated with those compounds. This versatile technique also allows us to include molecular mass spectrometry as a way of characterizing unknown organic peaks. The devised method holds promise as a more environmentally realistic means of direct measurement because it can be done at ambient pH and because the column utilizes a fluoropolymer resin that has minimal interaction with metal cations during the separation process. We applied this technique to a highly constrained set of soils representing different stages of pedogenesis. Leaching by known chelators and revealed striking patterns of metal-organic complexes for both iron and aluminum. These findings demonstrate the potential of HPLC-ICPMS as a useful tool with which to study spodosol formation and other processes of soil development.