Direct determination of P, V, Mn, As, Mo, Ba and U in seawater by SF-ICP-MS

A rapid high-throughput method is presented for the determination of trace elements (P, V, Mn, As, Mo, Ba and U) in seawater with application to tracing ballast water exchange in ocean-going vessels. By employing direct flow injection and methane addition the method is capable of >700 continuous determinations of ten-fold diluted seawater samples in less than 30 h. The utility and resolution of elemental tracers are enhanced when accuracy and precision are sufficient to provide determination errors that are negligible relative to oceanic variations. Here we demonstrate long-term precision <±7% (2-SD) and accuracy within the certified (2-SD) values for NASS-5 (n = 103; ten different analytical dates). Although all our values either agree very well (<5%; V and U) with suggested values or fall within (2-SD; Mn, As and Mo) the certified range of NASS-5, better agreement for Mo is expected. Our determined value of 9.1 μg L^-1 for Mo is more oceanographically consistent and in better agreement with other studies than the certified value (9.6 μg L^-1) and likely represents a more accurate value for NASS-5. We also suggest values of 17.7 μg L^-1 for P and 5.1 μg L^-1 for Ba, two elements that are uncertified and have no listed informative values. The new method could be expanded and applied to other problems in seawater analysis requiring high precision and sample throughput.