Elimination of the interference from nitrate ions on oxalic acid in RP-HPLC by solid-phase extraction with nanosized hydroxyapatite

A new method using solid phase extraction with nanosized hydroxyapatite for solving interference from nitrate ions on oxalic acid in reversed phase high performance liquid chromatography (RP-HPLC) was developed. The optimum experimental conditions for the separation and determination of oxalic acid were studied. After the interference was eliminated, oxalic acid was determined by RP-HPLC at the optimum chromatographic conditions with an average recovery ranging between 94.8% and 99.3%, and the relative standard deviations were less than 3.0%. This method was successfully applied to determine the oxalic acid in the xylem saps of tomato.