Solid Phase Extraction of Molybdenum on Modified Octadecyl Silica Sorbents in the Presence of Cationic Surfactants and on Silica-Based Anionic Exchanger and its Determination by Inductively Coupled Plasma Emission Spectrometry

Molybdenum was separated and preconcentrated as molybdate on microcolumns of octadecyl silica sorbents and silica-based strongly basic anion exchanger prior to its determination by ICP-AES. With octadecyl silica Separon SGX C18 and Separon SGX RPS, the retention of 0.01–0.4µg·mL^–1 Mo from 50–1000mL sample solutions was quantitative in the presence of the cationic surfactants carbethoxypentadecyltrimethylammonium bromide (Septonex^®), dodecylbenzyldimethylammonium bromide (Ajatin^®) or tetradecylbenzyldimethylammonium chloride (Zephyramine^®) at pH 6–8. 96% ethanol was the most suitable eluent of the molybdate/surfactant associate. For the strongly basic anion exchanger Separon SGX AX, the optimal conditions for sorption of 5–20µg Mo from 50–250mL sample solutions were at pH 2 in the presence of 0.05M ascorbic acid and ammonium citrate. 3M HNO₃ was a satisfactory eluent in this case. Organic solvents and excess of acids were removed by evaporation prior to the determination of Mo by ICP-AES in eluates. Both procedures can be used for the determination of ion-level molybdenum in waters.