A general approach to the speciation of metals present in mixed oxidation states is described. It employs the use of sequential spectrophotometric and atomic-absorption detectors in a flow injection system.The application of this approach is illustrated by two examples.(1) The determination of chromium(V1) and total chromium in corrosion test sea water: this system can operate at up to 120 injections per hour with an injected sample volume of 30yl. The working ranges are 1-50 p.p.m. of total chromium and 0.1-20 p.p.m. of chromium(V1). ( 2) The determination of iron(l1) and total iron in mineral process solutions: this system can also operate at up to 120 injections per hour using either a 20or a 100-yl sample. A 20-$ sample gave linear working ranges of 5-120 p.p.m. of total iron and 0.5-120 p.p.m. of iron(ll), and a 100-yl sample gave working ranges of 0.5-25 p.p.m. of total iron and 0.2-25 p.p.m. of iron(l1).

An alternative approach to that described in Part 1 for the speciation of mixed oxidation state metals is described. It employs parallel colorimetric flow injection manifolds with simultaneous sample introduction by coupled injection valves, An application of the approach is reported for the determination of iron(l1) and iron(ll1) with particular reference to mineral process liquors.The system can operate at up to 120 injections per hour using injected sample volumes of 20 pl for each manifold. The working ranges are 0.5-180 p.p.m. of iron(ll1) and 0.5-120 p.p.m. of iron(l1). Acid stability and interference studies in relation to mineral samples are reported, and also a novel use of the simplex optimisation procedure to minimise interference from copper(l1) ions.

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