E Medium Salts Stock (50×)
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1. Add about 600 mL of H2O to a 1-L beaker with a 50-mm magnetic stirring bar and place the beaker on a magnetic stirrer.
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2. Add the following, in the order below, waiting for each one to dissolve before adding the next:
| MgSO4-7H2O (Sigma-Aldrich 230391) | 10 g |
| Citric acid-1H2O (Sigma-Aldrich C1909) | 100 g |
| K2HPO4 (Sigma-Aldrich P3786) | 500 g |
| NaNH4HPO4-4H2O (Sigma-Aldrich S4172) | 175 g |
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3. (Optional) Heat to 45°C to facilitate dissolution.
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4. When the solution is at room temperature, adjust the volume to 1 L with H2O and pour the solution into a bottle.
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Do not autoclave.
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5. Add 3–5 mL of chloroform (Sigma-Aldrich 288306).
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The chloroform collects at the bottom of the bottle and keeps the solution sterile.
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6. Store at room temperature.
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This highly concentrated solution is stable for years. Beware not to include chloroform from the bottom when withdrawing liquid.
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