DETERMINATION OF OXALIC-ACID (ETHANEDIOIC ACID) IN SOIL EXTRACTS USING HIGH-PERFORMANCE LIQUID CHROMATOGRAPH

This paper describes a method for quantifying oxalate in soil HCl extracts using reversed-phase ion-pairing high performance liquid chromatography with UV detection at 220 nm. The method was adapted from a procedure for determining urinary oxalate (6). The mobile phase was 10 percent KH2PO4 and 5 mM TBA adjusted to pH 2.0 with H3PO4. The analytical column was a totally porous, reversed-phase silica based C-8 column (Hibar Li-Chrosorb(TM)). An important step in this method was the pre- treatment of each soil extract with a reversed-phase C-18 column (SPICE(TM) C-18). Sample pre-treatment removed complex, non-polar and low polarity compounds often present in soil extracts. The method was applied to calcareous, agricultural and organic soils materials. An oxalate accumulating fungus, Endothia Parasitica, was used as a verification of method applicability to plant-fungal materials. Oxalate extraction was accomplished by placing 1:2 suspensions (soil: 0.1 M HCl) on a reciprocal shaker for two hours and subsequently collecting the solution by filtering through a Whatman No. 42 filter paper. Coefficients of variation for replicate oxalate determinations were less than 10 percent. Recovery of oxalate from spiked extracts of soil and plant material were consistently between 82 and 104 percent. Detection limits were approximately 1-mu-M which was greater than the concentration of oxalate in saturation paste extracts. Oxalate was detected in some of these samples but could not be quantified.