Soil solutions, that is water contained within soil samples, have also been screened for their organic acid content. Organic acids measured in these samples include saturated and unsaturated mono- and dicarboxylic acids, keto-, hydroxy-, and also aromatic acids (Table 13.3). Organic acid concentrations are usually in the yM range.

Soil solutions are most often obtained by centrifugation, usually followed by filtration. Other procedures include column displacement techniques and saturation extracts.189 Depending on soil characteristics, soil solutions can vary in their composition, (e.g., organic acids, inorganic compounds, and complex organics such as humic substances), thus requiring varying degrees of pretreatment. Solutions obtained from sediments are often only filtered prior to their measurement with GC116 or IEC,115 whereas more complex soil solutions undergo further pretreatment prior to organic acid measurement employing AEC,107-109 IEC,110,111 or CZE.112,113 In order to streamline operations one application developed an on-line sample pretreatment scheme which includes cation and anion exchange, and also extraction with TOPO- impregnated membranes.108 This approach has been utilized in a subsequent study, thus demonstrating its usefulness.107 Because of the similarity in their matrices, methods employed for groundwater may also be applied to soil solutions.14,47,48,101

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