Direct Determination of Dissolved Phosphate and Silicate in Seawater by Ion Exclusion Chromatography Sector Field Inductively Coupled Plasma Mass Spectrometry

A method is described for the direct determination of dissolved phosphate and silicate in seawater using ion exclusion chromatography (IEC) coupled with sector field inductively coupled plasma mass spectrometry (SF-ICPMS). Dissolved silicate was determined by double isotope dilution using a (29)Si spike, whereas one point gravimetric standard addition with internal standard of the same (29)Si spike was employed to quantitate dissolved phosphate. Medium resolution was used for all measurements in order to resolve polyatomic interferences on Si and P isotopes. Concentrations of 1.670 ± 0.008 and 30.20 ± 0.09 μM (SD, n = 6) with precisions of 0.47 and 0.31% for the dissolved phosphate and silicate, respectively, were obtained in National Research Council Canada certified reference material MOOS-3 seawater, in good agreement with certified values of 1.60 ± 0.15 and 30.5 ± 0.8 μM (U, k = 2), respectively. The reported method is a rapid (10 min per run), simple, and accurate online technique that requires no sample pretreatment. Moreover, this procedure achieves <0.5% precision (at above analyte concentrations) and method detection limits of 0.006 and 0.004 μM (0.18 as P and 0.11 ng g(-1) as Si), respectively, using a of 100 μL injection of seawater. The proposed technique is robust and well-suited for the determination of dissolved phosphate and silicate in seawater.