Low iron concentration (as low as 0.02 nM) in the open ocean limits phytoplankto
ID: 920067 • Letter: L
Question
Low iron concentration (as low as 0.02 nM) in the open ocean limits phytoplankton growth. Preconcentration is required to determine such low concentrations. Trace Fe^3+ from a large volume of seawater is concentrated onto a 1.2-mL chelating resin column. The column is then rinsed with 30 mL of high-purity water and eluted with 10 mL of 1.5 M high-purity HN0_3. For each sample, seawater is passed through the column for 17 hours at 10 mL/min. How much is the concentration of Fe^3+ in the 10 mL of HN0_3 eluate increased by this preconcentration procedure?Explanation / Answer
Sample volume V= 10 mL/min x 17 h x 60 min/h / 1000 mL/L = 10.2 L
10200 mL (sample volum) / 10 mL (eluted sample) = 1020 times.
Ignoring this is reagent impurity and calculating for sea water
190 ppb /1020 = 0.186 ppb = 0.186 x 10-9g/mL = 0.186 x 10-6g/L =
0.186 x 10-6g/L / 56 g/mol = 0.003 x10-6 M = 3 nM
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