COMPARISON OF ON-COLUMN AND PRECOLUMN DERIVATIZATION FOR LIQUID-CHROMATOGRAPHIC DETERMINATION OF MOLYBDENUM IN SEAWATER AND BOVINE LIVER

A rapid, accurate, and sensitive method was developed for the determin ation of molybdenum in seawater and bovine liver-samples by reversed-p hase liquid chromatography (LC) using a C-18 column, The method was;ba sed on chelation of the metal with 8-hydroxyquinoline by on-column or precolumn derivatization followed by LC elution with acetonitrile-0.02 M acetate buffer (3 + 2; pH 4.7) and 1 x 10-(3)M of the ligand as the mobile phase. The spectrophotometric detection was made at 390 nm. Dat a obtained from the 2 derivatizations (on- and precolumn chelation) we re compared in terms of detection limit, precision, accuracy, and ease of LC determination of molybdenum. No significant difference exists i n the detection limit and the sensitivity of the 2 methods. However, t he on-column chelation method, that is, the direct injection of aqueou s samples onto the column, showed relatively less interference from ma nganese and greater simplicity in operation compared with precolumn ch elation; therefore, on-column chelation is preferable for routine anal yses. The on-column method produced mean levels of 9.6 +/- 0.4 mu g/L for the seawater sample and 3.6 +/- 0.2 mu g/g (certified value, 3.5 /- 0.5 mu g/g) for bovine liver.