User:Jacob Esenther/Notebook/Chem 571/2014/09/02

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  1. Create the Stock NaOH Solution
  2. Select 5 Amino Acids
  3. Standardization by Simple Titration
  4. Titration of Amino Acids


  1. Create the Stock NaOH solution
    1. Create 500 mL of 0.15M NaOH stock solution
    2. Calculations show that the solution will require 3.0772g of NaOH
  2. Select Amino Acids
    1. The five amino acids selected were Cysteine, L-Glutamine, Glycine, Lysine, and Tryptophan
  3. Standardization performed by simple titration with potassium hydrogen phthalate (KHPhth)
    1. Obtain a clean buret
    2. Rinse the buret with about 10 mL of your NaOH solution. Be sure to drain some through the tip. You may use a funnel to fill.
    3. Empty completely and repeat 1 - 2 times.
    4. Fill completely with NaOH and drain some through the tip. Tap to remove all air bubbles. Remove the funnel.
    5. Record the initial volume. It does not have to equal one, but you need at least 25 mL of titrant. Remember, top line reads 0 mL.
    6. Transfer about 0.5 g of KHPhth to an Erlenmeyer flask and add 15 - 30 mL of water.
    7. Or, transfer 20 mL of 0.2 mM KHPhth that you have prepared (or 1 mL of 4 mM if you needed higher mass for accuracy)
    8. Add a few drops of methyl red phenolphthalein solution
    9. Titrate until the solution turns orange pink. If it is yellow dark red, you overshot. You can periodically rinse sides with wash bottle.
    10. Repeat at least twice
  4. Titration of Amino Acids
    1. Use the actual concentration of the NaOH stock solution to calculate the amount of AA needed to titrate with 20mL of stock solution
    2. Transfer the solid amino acid to a clean and dry 100 mL beaker.
    3. Add 10mL of 20mM HCl and 10mL water
    4. insert the pH probe and record the initial value
    5. Titrate each AA twice and take periodic measurements of the pH
      1. The first run should be general to find where the titration point is
      2. The second run should use smaller increments around the predicted titration point.
    6. From the recorded pH valued, create a titration curve for the five AAs.
    7. Add titrant in 4 mL intervals. Swirl gently, being careful not to splash. Record the pH.
    8. Continue until the pH reaches at least 10 or 11.
    9. For the first trial, you will likely skip past the inflection points. On 2nd & 3rd trials, slow addition to 0.2 or 0.1 mL near inflections.
    10. Repeat for all 5 amino acids

NaOH Stock Solution Data

NaOH Stock Solutions

NaOH solution concentration.jpg

Amino Acid Titration Data

  • Note - The first calibration of the pH detector did not register. These are single calibration titrations.
  • Note - All 2nd trials were preformed with 1mL 1M HCl rather than the original 10mL.

Cysteine pH table.jpg

  • During the second titration, 15mL of DI water was used

Glutamine pH table.jpg

  • During the second titration, 20mL of DI water was used

Glycine Table.png

Lysine pH table.jpg

Tryptophan pH table.jpg

  • During the first titration, 2mL of 1M HCl and 20mL of DI water was used
    • There is no pH data for the first titration because too much HCl was added
  • During the second titration, the mass of Tryptophan was cut from 0.6044g to 0.2015g to make dissolving in solution more practical
    • 1mL of HCl and 27mL of DI water were used

Creation of Amino Acid Stock Solutions

Stock solutions of the amino acids mentioned above were made for use in UV-Vis analysis, and fluorimetric analysis. Stock solutions were made using the specifications from the chart below.

Uv-vis prep chart.jpg