EGTA Solution (100 mm)

• 1. Add 3.804 g of EGTA (e.g., Sigma-Aldrich >99%) to 50 mL ultrapure water in a plastic beaker.

• 2. Add 20 mL KOH (make fresh from KOH concentrate, e.g., Fluka).

• 3. Add 0.238 g HEPES free-acid form (e.g., Sigma-Aldrich ≥99.5%; 25 mm final concentration).

• 4. Stir solution; add KOH slowly until pH remains stable at 7.0.

• 5. Store at 4°C. (This solution is good for up to 3 mo.)

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