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A method for the direct determination of dissolved silica in seawater by ion chromatography (ion-exclusion mode) in combination with inductively coupled plasma mass spectrometry is described. This method (ICE-ICPMS) was developed as a second, independent method to complement the usual colorimetric procedure in the determination of a certified value of dissolved silica concentration in a planned seawater reference material. Ion exclusion affords a separation of the dissolved silica not only from the major seawater cations but also from potentially interfering anions (chloride, sulfate, carbonate, bicarbonate, and borate). The detection limit, conservatively estimated at 2.3 ng/g as Si in seawater (0.08 muM), is superior to that achievable by direct analysis by inductively coupled plasma atomic emission spectrometry. A comparison of results of six pairs of determinations by the ICE-ICPMS method and the standard colorimetric method is shown in Table 1.
