1. pH Indicators
Biotechnology I

2. Review Question Why is the pH scale logarithmic?
Why do we care about pH in biotechnology?

3. Essential Question(s)
How is pH measured?
What is a pH indicator?
How is it used in pH measurements?

4. pH Measurement pH can be measured several ways pH indicator dyes
pH strips
pH meter/electrode

5. pH indicator dyes
Dyes whose color is pH dependent and whose color changes at specific pH
Example: Phenolphthalein
Changes from colorless to red between pH 8 and 10

6. pH indicators Advantages Disadvantages Inexpensive, simple to use
Show at best pH about 0.3 pH units apart
Allows investigator to quickly evaluate whether solution acidic, basic or neutral
Useful for monitoring pH
Disadvantages
Do not change color sharply at a single pH
Cannot be used in certain types of solutions

7. Types of pH Indicators

8. Examples of Use in Biotechnology
Add nontoxic nonreactive indicator dye to human cell culture media
Provides immediate visible information about the pH status of culture medium
Ex, phenol red
Culture healthy – shade of pink
Culture becoming acidic – yellow tinge
Indicates culture requires attention

9. Possible Errors associated with Indicators
pH indicators- weak acid/bases
If solution not buffered can change pH
Color altered by
High salt >0.2 M
Solvent
Reaction with proteins

10. Lab Instructions