Low iron concentration (as low as 0.02 nM 0.02 nM) in the open ocean limits phytoplankton growth. Preconcentration is required to determine such low concentrations. Trace Fe3+Fe³⁺ from a large volume of seawater is concentrated onto a 1.2-mL1.2-mL chelating resin column. The column is then rinsed with 30mL 30mL of high-purity water and eluted with 10 mL 10mL of 1.5 M 1.5 M high-purity HNO₃.HN0₃.

a. For each sample, seawater is passed through the column for 17 h 17 h at 10 mL/min.10 mL/min. How much is the concentration of Fe3+Fe³⁺ in the 10 mL 10 mL of HNO₃HNO₃ eluate increased by this Preconcentration procedure?

b. What is the concentration of Fe3+Fe³⁺ in the seawater when 57 nM 57 nM Fe3+Fe³⁺ is found in the nitric acid eluate?

c. Reagent-grade concentrated nitric acid is 15.7 M 15.7 M and contains ≤ 0.2 ppm ≤ 0.2 ppm iron. What would be the apparent concentration of Fe (nM) Fe (nM) in a seawater blank if reagent-grade acid were used to prepare the 1.5 M 1.5 M HNO3 HNO₃ eluent?