Potentiometric Titration of the PC2-Cd2 System and Analysis Using

Potentiometric Titration of the PC2-Cd2+ System and Analysis Using the BEST Program20 21 

Prepare 100 ml of 0.5 M aqueous NaOH using carbonate-free ddH20 and standardize using the primary standard, potassium hydrogen phthalate (MM = 204.22 g mol-1)  

Prepare 25 ml of aqueous 0.4 M glycine (free base, zwitterionic form— +H3NCH2COO ), or 0.4 m cysteine (hydrochloride salt, Cl-+H3NCHCH2 SHCOOH). 

Into a 400 ml beaker, place 100 ml of 0.2 M KNO3 (gly) or 6 M NaCI (cys), 10 ml amino acid, and 90 ml H20. Note that the pH for glycine should be 6. For cysteine, neutralize the C-terminus by adding 1 equiv. of NaOH. Record initial pH and the room temperature. 

Using a burette and with stirring, titrate your amino acid solution with the standardized 0.5 M NaOH solution in 0.5 ml aliquots until pH 12. After each addition, record the exact amount of NaOH added and the corresponding pH. 

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