A method of matrix elimination has been developed that facilitates the determination of analytes such as arsenic, chromium, selenium and vanadium in biological matrices by inductively coupled plasma mass spectrometry (ICP-MS) without interference from polyatomic ions. The method involves the retention of the analytes as anions on activated alumina (acidic form) in a microcolumn using an on-line flow injection system, with simultaneous matrix removal. Analysis of certified reference materials [NIES (National Institute of Environmental Studies) 9 Sargasso, Tort-1 Lobster Hepatopancreas, Dorm-1 Dogfish Reference Muscle and Dolt-1 Dogfish Liver Tissue] yielded results in good agreement with the certified values, although a photolysis step was used for determinations of arsenic in animal based samples in order to destroy organoarsenic compounds. Tests showed close to 100% recovery for all analytes. The limits of detection (3σ_n–1) using a 200 µl sample loop were 1.2, 6.0, 9.0 and 65 ng ml^–1 for vanadium, chromium, arsenic and selenium, respectively. A preconcentration system was developed for selenium because of the relative insensitivity of ICP-MS to this element. This yielded a detection limit of 1.0 ng ml^–1 at m/z 78.