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 determination of molybdenum in seawater and bovine liver samples by reversed-phase liquid chromatography (LC) using a C18 column. The method was based on chelation of the metal with 8-hydroxyquinoline by on-column or precolumn derivatization followed by LC elution with acetonitrile-0.02M acetate buffer (3 + 2; pH 4.1) and 1 x 10(-3)M of the ligand as the mobile phase. The spectrophotometric detection was made at 390 nm. Data obtained from the 2 derivatizations (on- and precolumn chelation) were compared in terms of detection limit, precision, accuracy, and ease of LC determination of molybdenum. No significant difference exists in the detection limit and the sensitivity of the 2 methods. However, the on-column chelation method, that is, the direct injection of aqueous samples onto the column, showed relatively less interference from manganese and greater simplicity in operation compared with precolumn chelation; therefore, on-column chelation is preferable for routine analyses. The on-column method produced mean levels of 9.6 +/- 0.4 micrograms/L for the seawater sample and 3.6 +/- 0.2 microgram/g (certified value, 3.5 +/- 0.5 microgram/g) for bovine liver.