Determination of nanomolar levels of nutrients in seawater

Nutrients (phosphate, nitrate, nitrite, ammonium and silicate) exert strong controls on oceanic primary productivity. In oligotrophic areas, which cover approximately 40% of the world's oceans, nutrient concentrations can drop to nanomolar levels or lower due to biological uptake, so highly sensitive methods and technologies are urgently needed for nutrient measurements in such areas. In this work, we review procedures for phosphate and nitrite/nitrate analyses published since the review of Patey et al. [32], and procedures for analysis of ammonium and silicate at nanomolar levels. Our review includes aspects of measurement protocols that bear strongly on the quality of analyses of trace nutrients, including contamination of reagents, sample storage, and preparation of nutrient-free seawater. This review excludes methods that have limits of detection greater than 1 mu M, and methods that are not specific to seawater. (C) 2014 Elsevier B.V. All rights reserved.