Appropriate bottles for storing seawater samples for dissolved organic phosphorus (DOP) analysis: A step toward the development of DOP reference materials

Abstract

Reference materials (RMs) are essential to ensure comparability of oceanographic chemical measurements. Since dissolved organic matter (DOM) plays a significant role in bioactive element cycles such as carbon (C), nitrogen (N), and phosphorus (P), measurements of dissolved organic C, N, and P (DOC, DON, and DOP) have been paid much attention. Although RMs that target DOC and DON analyses have been developed, no comparable studies have been conducted for DOP analysis. This study examined the selection of the most appropriate bottle to store DOP samples to develop an RM for DOP. Natural seawater samples were stored in bottles made from various plastic materials and glass, and the temporal change in DOP and DOC concentrations were measured during a storage period of months to a year in the dark under 25°C. I found that severe contaminations of DOP and/or DOC occurred in some bottle types. Whereas DOP concentrations were unchanged in many bottle types, the concentrations of both DOP and DOC were stable only in glass and perfluoroalkoxy (PFA) bottles. I conclude that these two bottle types have potential as an appropriate sample bottle for RMs of DOP, this is because colloids formed via DOC contamination during storage can potentially bond with phosphate in the sample and thus inorganic phosphate may be measured as DOP contamination.