ION CHROMATOGRAPHY METHODS FOR THE SIMULTANEOUS DETERMINATION OF MINERAL ANIONS IN PLANT SAP

The use of two ion chromatographic systems, with and without a chemica l conductivity suppressor, is described for the determination of Cl-, NO3-, PO43- and SO42- in plant sap. Samples were prepared just by dilu tion. Separations have suffered from interference due to the presence of other solutes. Usually, organic acid ions such as malate coelute wi th sulphate ions on the nan-suppressed system. An appropriate eluent, formed with boric and tartaric acids at pH 4.0, was used to overcome t his problem. Organic acids were eliminated in the void volume but phos phate appeared as a negative peak and cannot be quantitated. Suppresse d ion chromatography permits the measurement to be performed with more efficiency, but coelutions also occurred with carbonate-hydrogencarbo nate eluent for Cl- and SO42-. The best separation of ions was achieve d on the Dionex AS 11 column with a sodium hydroxide gradient elution and a 5 min running time. The selectivity and sensitivity of the metho ds are discussed.