Validation of Ti(III) as a reducing agent in the chemiluminescent determination of nitrate and nitrite in seawater

Titanium (III) trichloride is validated here for the quantitative conversion of all nitrate plus nitrite in seawater to nitric oxide gas, thereby providing an alternative to the typically used reducing agent, ferrous ammonium sulfate plus ammonium molybdate, in the chemiluminescent detection of nitrate plus nitrite at the nanomolar level. We find that both Fe(II) + Mo(VI) and Ti(III) methods yield identical results for standards and seawater samples over a validated concentration range of 1 to 1000 nM, and are both in agreement with traditional colorimetric results. Benefits of the Ti(III) reduction chemistry are: simpler preparation, decreased ammonium contamination in a laboratory that measures low-level nutrients, 30% reduction of the sulfuric acid catalyst, and a higher sample through-put. Most importantly, though, this work can be considered the first step on a path toward a much-needed, direct measurement of dissolved organic nitrogen concentrations, as has already been achieved for dissolved organic carbon.