ADVANCING A NEW METHOD FOR THE DIRECT DETERMINATION OF DISSOLVED ORGANIC NITROGEN (DON) IN SEAWATER
Attempts to establish a method for the direct determination of DON in natural waters have been met with various obstacles, to the point that DON is still typically reported as the difference between total dissolved nitrogen (TDN) and dissolved inorganic nitrogen (DIN: nitrate, nitrite and ammonium). This approach works relatively well in the ocean’s uppermost water column, since TDN is a significantly larger number than DIN (in most cases), leading to tolerable error estimates on DON values. In deep, open-ocean water, DIN accounts for the majority of TDN, resulting in errors of 50% or more on DON values. Therefore, a direct method to quantify DON is needed in order to establish a reliable mass balance of nitrogen in the lower ~80% of the open ocean. The basic, yet historically difficult, goal of a direct DON method is to eliminate DIN while completely preserving, and minimally contaminating, the DON content of the seawater. Through work on the chemiluminescent detection of low-level nitrate plus nitrite, we have recently validated that Ti(III) quantitatively reduces nitrate and nitrite to NO gas (Foreman et al., 2016; Marine Chemistry 186:83–89), which can be easily stripped from solution. As a pre-treatment for DON analysis, we find that only 0.06% (w/v) TiCl3 in solution removes >50 micromolar nitrate from a seawater sample. Following pre-treatment, samples are irradiated in an UV light chamber to photo-oxidize DON to nitrate. Preliminary data shows that we can successfully recover 85% of DON; with additional work, we hope to recover 100% of DON.
Foreman, R. K., University of Hawaii - Manoa, USA, email@example.com
Karl, D. M., University of Hawaii - Manoa, USA, firstname.lastname@example.org
Location: 304 A/B
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