Z8

Fe-EDTA solution for Z8 — stock solution "A" (iron)

per 100 mL · storage at 4 °C in dark glass, 6 months

Fe-EDTA solution for Z8 — stock solution "B" (EDTA)

per 100 mL · storage at 4 °C, 6 months

Fe-EDTA solution for Z8 — working solution

per 1 L · usage rate 10 mL per 1 L of medium · storage at 4 °C, 3 months

Gaffron trace element solution

per 100 mL of solution · usage rate 1 mL per 1 L of medium · storage at 4 °C, 12 months

Prepared from two stock solutions. Stock solution 1 (per 1 L): NaNO₃ 46.7 g + Ca(NO₃)₂·4H₂O 5.9 g + MgSO₄·7H₂O 2.5 g. Stock solution 2 (per 1 L): K₂HPO₄ 3.1 g + Na₂CO₃ 2.1 g. To 900 mL of water add 10 mL of stock solution 2 → 10 mL of the Fe-EDTA working solution → 1 mL of Gaffron solution → last of all 10 mL of stock solution 1 (it contains the calcium) → make up to 1000 mL.

• Stock solutions 1 and 2 must be stored strictly separately: mixing the concentrates directly causes CaCO₃ to precipitate instantly.
• The Fe-EDTA solution is prepared in three steps — two stock solutions, "A" in acid and "B" in alkali, and then a dilute working solution. This is the only way to obtain a stable complex without iron hydroxide precipitating.
• Nitrogen-free variant Z8₀ (Z8X): omit NaNO₃ and Ca(NO₃)₂·4H₂O and replace the calcium nitrate with CaCl₂·2H₂O at 0.036 g/L (an equimolar substitution with respect to calcium).
• Its low ionic strength makes Z8 convenient for isolating strains from oligotrophic water bodies and soil samples, where cultures tolerate the rich BG-11 poorly.
• Prepared in dilute hydrochloric acid rather than in water: at neutral pH FeCl₃ hydrolyses and Fe(OH)₃ precipitates.
• Prepared in dilute alkali: EDTA is poorly soluble under acidic conditions. Stock solutions "A" and "B" are stored separately and are never mixed in concentrated form.
• Stock solution "A" is poured into the water first, then stock solution "B" is added with stirring — complex formation proceeds in dilute solution without any precipitate forming. The finished solution is clear and straw-yellow. The appearance of brown Fe(OH)₃ flocs means the solution is unusable.
• V₂O₅ is insoluble in water — dissolve it beforehand in 0.2–0.3 mL of warm 1 M NaOH and only then add it. Store KI in the dark: in the light it is oxidised to I₂ and the solution turns yellow. The solution contains cadmium salts — work in a fume hood and send spent solutions for proper disposal.