Determination of Oxalate in Forage by Reverse-Phase High Pressure Liquid Chromatography

¹ USDA, Agricultural Research Service, US Dairy Forage Research Center, Missouri Cluster, University of Missouri, Columbia 65211 and University of Missouri, Columbia 65211

A method for extraction, derivatization, and determination of oxalate from forage is described. Alfalfa and tall fescue were extracted with either water or 1 N HCl. Oxalate decarboxylase (EC 4.1.1.2) was used to destroy oxalic acid so that other derivatizable compounds could be determined. The derivatizing agent o-phenylenediamine was reacted with oxalic acid in plant extracts to form 2,3-dihydroxyquinoxalene. Aliquots of derivatized extract were fractionated using disposable C-18 minicolumns. Collected fractions were analyzed for 2,3-dihydroxyquinoxalene using UV detection of reverse phase HPLC eluent. Using water or 1 N HCl extraction, plant oxalates were determined as water-soluble or water-insoluble fractions, respectively. Recovery of oxalate from forage samples was 80 to 112% of added oxalate. Data confirm that differences are greater between alfalfa and tall fescue than within these forage species.

Key Words: forage • oxalate solubility • calcium solubility

Submitted on April 17, 1989
Accepted on September 1, 1989