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Precipitate formation during PH adjustment - (May/03/2009 )

I had posted this question (below) before, the suggestions given were helpful but i am experiencing precipitate formation when i adjust the buffer PH using NaOH.

(ii)Is the Cacl2(0.4M) high for an extraction buffer?

Thank you

I am preparing an extraction buffer for peroxidase assay in plant material. According to the method i should extract in 100ml 0.1M (pH 6.2) citrate buffer containing 5% PVPP and 0.4 M calcium chloride.

I managed to prepare 1 liter of 0.1M (pH 6.2) citrate buffer using citric acid and sodium citrate. Then i dissolved the required concentration of calcium chloride and the pH dropped to 4.6. I feel there is an error in my addition of CaCl2. what should i do to maintain the pH at 6.2?


I do not think you should use NaOH to adjust the pH. How about using Tris-base or other organic buffer?

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The best way to do so will be to cut the citric acid and increase Na citrate.