Silicon concentration is one of the key issues to be studied for seawater, specially attentions paid for marginal sea samples, too. The concentration of total silicon can be determined by inductively coupled plasma mass spectrometry (ICP-MS), which is the most powerful instrument for elelmental analysis. However, the measurement of silicon isotopes by ICP-MS suffers spectral interferences from polyatomic ions such as N₂⁺, N₂H⁺, and NO+, making it challenging for seawater specially for low silicon samples. Separation of silicon from the sample matrix is ofen required for measuring silicon isotopes and limits the efficiency of application. In the present work the capability of tandem quadrupole ICP-MS for suppressing spectral interferences was investigated in detail to acheive a set of optimum operating conditions for measuring silicon isotopes. The best performance can be acheived with oxygen-hydrogen and ozone-hydrogen as the reaction cell gases, respectively. Both sets of operating conditions provide background equivalent conentrations and limit detections under 0.3 ng/g for the full set of silicon stable isotopes, i.e. ²⁸Si, ²⁹Si, and ³⁰Si.  Determination of silicon in three seawater certified reference materials (CRMs), i.e. NMIJ CRM 7601-a, 7602-a,  and 7603-a were  conducted. The results for higher Si-concentration CRMs (7602-a and 7603-a) were in agreement  with certified values, while the results for lower Si-concentration CRM (7601-a) was apprently higher than the certified values. Further investigation was conducted to confirm the species of silicon in NMIJ CRM 7601-a. The results indicate that Si-nano-particles contribute to the relative higher Si-concentration observed, since that the CRMs are certifed for dissolved silicon. Details about the experiment will be presented on the conference.  

seawater,SP-ICP-MS,Si,ID-ICP-MS,nano-particle