AOAC Official Method 937.03 Iron in Plants
Colorimetric Method
First Action 1937
Final Action
A. Reagents
(a) Acetic acid.—2M.Dilute 120 gCH3COOHto 1LwithH2O.
(b) Ammonium citrate solution.—1%. Dissolve 1 g ammonium citrate in H2O and dilute to 100 mL.
(c) Bromophenol blue indicator.—0.04%. Grind 0.1 g bromophenol blue in mortar with 3 mL 0.05M NaOH, transfer to volumetric flask, and dilute to 250 mL with H2O.
(d) Buffer solutions.—(1) pH 3.5.—Mix 6.4 mL 2M CH3COONa with 93.6 mL 2M CH3COOH and dilute to 1 L. (2) pH 4.5.—Mix 43mL2MCH3COONawith 57mL2MCH3COOHand dilute to 1 L.
(e) Hydroquinone solution.—Dissolve 1 g hydroquinone in 100mLpH 4.5 buffer, (d)(2). Keep in refrigerator, and discard when any color develops.
(f) o-Phenanthroline solution.—Dissolve 1 g o-phenanthroline× H2O in H2O, warming if necessary, and dilute to 400 mL.
(g) Sodium acetate solution.—2M. Dissolve 272 g CH3COONa×3H2O in H2O and dilute to 1 L.
(h) Iron standard solution.—1 mg/mL. Dissolve 1 g electrolytic Fe in 50 mL H2SO4 (1 + 9), warming if necessary to hasten reaction.Cool, and dilute to 1 L with H2O.
