Examination of precipitation chemistry and improvements in precision using the Mg(OH)2 preconcentration inductively coupled plasma mass spectrometry (ICP-MS) method for high-throughput analysis of open-ocean Fe and Mn in seawater

The chemistry of magnesium precipitation preconcentration of Fe, Mn, and Co from seawater was investigated, and this analytical technique was adapted for use with the Element-2 inductively coupled plasma mass spectrometer (E2 ICP-MS). Experiments revealed that the scavenging efficiency of Mn using the precipitation protocol described here was ∼95% and similar to that previously observed with Fe. In contrast, the scavenging efficiency of Co was three-fold lower than that of Fe and Mn, resulting in poor recovery. An increase in sample size to 13 mL led to several desired effects: (1) an increase in the Fe and Mn signals allowing a final dilution of samples to 0.5 mL and the use of an autosampler, (2) an increase in precision to ∼1–2.5% R.S.D., and (3) an increase in signal relative to the blank. Experiments suggest metal concentration from seawater occurs during the formation of Mg(OH)2 precipitate, whereas P was scavenged by adsorption onto the Mg(OH)2 particles. Example vertical profiles are shown for dissolved Fe and Mn from the Equatorial Pacific.