- Create the Stock NaOH Solution
- Select 5 Amino Acids
- Standardization by Simple Titration
- Titration of Amino Acids
- Create the Stock NaOH solution
- Create 500 mL of 0.15M NaOH stock solution
- Calculations show that the solution will require 3.0772g of NaOH
- Select Amino Acids
- The five amino acids selected were Cysteine, L-Glutamine, Glycine, Lysine, and Tryptophan
- Standardization performed by simple titration with potassium hydrogen phthalate (KHPhth)
- Obtain a clean buret
- 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.
- Empty completely and repeat 1 - 2 times.
- Fill completely with NaOH and drain some through the tip. Tap to remove all air bubbles. Remove the funnel.
- 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.
- Transfer about 0.5 g of KHPhth to an Erlenmeyer flask and add 15 - 30 mL of water.
- 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)
- Add a few drops of methyl red phenolphthalein solution
- Titrate until the solution turns orange pink. If it is yellow dark red, you overshot. You can periodically rinse sides with wash bottle.
- Repeat at least twice
- Titration of Amino Acids
- Use the actual concentration of the NaOH stock solution to calculate the amount of AA needed to titrate with 20mL of stock solution
- Transfer the solid amino acid to a clean and dry 100 mL beaker.
- Add 10mL of 20mM HCl and 10mL water
- insert the pH probe and record the initial value
- Titrate each AA twice and take periodic measurements of the pH
- The first run should be general to find where the titration point is
- The second run should use smaller increments around the predicted titration point.
- From the recorded pH valued, create a titration curve for the five AAs.
- Add titrant in 4 mL intervals. Swirl gently, being careful not to splash. Record the pH.
- Continue until the pH reaches at least 10 or 11.
- 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.
- Repeat for all 5 amino acids
NaOH Stock Solution Data
NaOH Stock Solutions
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.
- During the second titration, 15mL of DI water was used
- During the second titration, 20mL of DI water was used
- 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.