Dataset: La Jolla Nearshore Biogeochemistry

For NO3: Instrument utilizes an analytical method where N-1-N (NEDD) and sulfanilamide are reacted with the sample to form a red dye, which is measured at an absorbance of 520-540 nm. For nitrate analysis, the nitrate is first reduced to nitrite by the sample being mixed with a buffer solution (ie., Ammonium Chloride or Imidazole) and passed over a cadmium column that has been treated with copper sulfate, which catalyzes the reduction reaction. The resulting nitrite is then analyzed and the final output for the ‘nitrate’ channel is a sum of both nitrate and nitrite. It is important therefore to analyze nitrite separately so that nitrate can be determined by subtracting from the total nitrate plus nitrite concentration (Becker et al., 2019).

For analysis of PO4 in seawaters acidic solution of molybdate is added, followed by the addition of a reducing compound (dihydrazine sulfate or ascorbic acid) to form a phospho-molybdenum blue complex with the absorbance measured at approximately 820 or 880nm, depending on the method and availability of filters (Becker et al., 2019).

For analysis of SIL, acidified ammonium molybdate is added to a seawater sample to produce silicomolybdic acid, which is then reduced to a silicomolybdenum blue complex following the addition of stannous chloride or ascorbic acid, and measured at 660nm for stannous chloride or 820nm for ascorbic acid (Becker et al., 2019).

For NO2: Instrument utilizes an analytical method where N-1-N (NEDD) and sulfanilamide are reacted with the sample to form a red dye, which is measured at an absorbance of 520-540 nm. For nitrate analysis, the nitrate is first reduced to nitrite by the sample being mixed with a buffer solution (ie., Ammonium Chloride or Imidazole) and passed over a cadmium column that has been treated with copper sulfate, which catalyzes the reduction reaction. The resulting nitrite is then analyzed and the final output for the ‘nitrate’ channel is a sum of both nitrate and nitrite. It is important therefore to analyze nitrite separately so that nitrate can be determined by subtracting from the total nitrate plus nitrite concentration (Becker et al., 2019).

For NH3: In the fluorometric method, without using any membrane diffusion, the sample is combined with a working reagent made up of OPA, sodium sulfite, a borate buffer, and then heat to 75°C. Fluorescence proportional to the ammonium concentration is measured at 460nm following excitation at 370nm (Becker et al., 2019).