AOAC Official Method 941.03 Zinc in Plants

Mixed Color Method
First Action 1941
Final Action
A. Reagents
(Redistil all H2O from Pyrex. Treat all glassware with HNO3 [1 +1] or fresh chromic acid cleaning solution. Rinse repeatedly with ordinary distilled H2O and finally with Zn-free H2O.)
(a) Carbon tetrachloride.—UseACSgrade without purification.If technical grade is used, dry with anhydrous CaCl2 and redistil in presence of small amount CaO. (Used CCl4 may be reclaimed by distillation in presence of NaOH [1 + 100] containing small amounts of Na2S2O3, followed by drying with anhydrous CaCl2 and fractional distillation in presence of small amounts of CaO.) (Caution: See Appendix
B, safety notes on distillation and carbon tetrachloride.) (b) Zinc standard solutions.—(1) Stock solution.—1 mg/mL.
Place 0.25 g pure Zn in 250mLvolumetric flask. Add ca 50mLH2O and1mLH2SO4; heat on steam bath until all Zn dissolves. Dilute to
volume and store in Pyrex vessel. (2) Working solution.—10mg/mL. Dilute 10 mL stock solution to 1 L. Store in Pyrex vessel.
(c) Ammonium hydroxide solution.—1M. With all-Pyrex apparatus distil NH4OH into H2O, stopping distillation when half has distilled.Dilute distillate to proper concentration. Store in glass-stoppered Pyrex vessel.