Development of an analytical protocol for the determination of V (IV) and V (V) in seawater: Application to coastal environments

A new method was developed for determining vanadium [V (IV) and V (V)] species in seawater by using a solid-phase extraction at pH 4.5 with Chelex-100 resin. Vanadium (V) was eluted with 0.1 M ammonium hydroxide and V (IV) was eluted with 0.2 N perchloric acid. The recovery of V species in synthetic seawater was > 95% for V (V) and 92% for V (IV) at a concentration of 40 nM, typical of open ocean waters. Stability experiments showed V (IV) was relatively stable for over 24 h. The detection limit for V (IV) and V (V) was on the order of 0.5 nM. The analytical precision was ~ 10% in the concentration range of 10 nM. The speciation method was applied to coastal water samples collected at the head of the Peconic River Estuary and in the Long Island Sound (LIS) during the Spring and Summer of 2005. Concentrations of dissolved total V ranged from 6.0 to 35 nM in both coastal environments. Consistent with thermodynamic considerations, the dominant V form in the study areas was V (V). However, V speciation varied seasonally and spatially in response to redox changes. Reduced V (IV) accounted for 5–20% of the total dissolved pool in coastal waters of LIS and about 40% of total V at the head of the Peconic River Estuary.