Measuring and controlling pH - it's one of those things that as a biomanufacturing
technician you're going to be doing all the time. Almost every biotech product requires a carefully
maintained pH level in order to get the results you're after. If a solution becomes too acidic
or too basic - well the product is ruined. So how do we prevent that from happening?
We use buffers. Buffers are solutions that are good at neutralizing ions. That means they're able
to resist changes in pH even when we add acids or bases. In this experiment, we're going to test a
simple buffer to see how well it maintains its pH by comparing it to deionized water. Always make
sure to wear your PPE - lab coat, gloves, and safety glasses. So let's make our buffer. It's
equal parts acetic acid and sodium acetate. Pour 100 milliliters of the buffer into 150 ml beaker
and label it. Add a stir bar and turn on the stir plate. Over here we have a similar setup, but
this beaker contains our control - the deionized water. Insert a pH meter probe into both beakers
and let's take our initial pH readings. The buffer is 4.44 and the deionized water is 6.73.
We'll need to record these readings in our lab notebook. We're going to do this experiment
twice. First time through we'll add acid to both beakers and compare the change in pH.
The second time through we'll test it with a base. All right - let's go. Pipette one
milliliter of hydrochloric acid into each beaker, and let's watch to see what happens to the pH.
Our buffer just barely drops to 4.45, but look at the deionized water - it dropped all
the way to 1.66. Add another milliliter of hydrochloric acid to each beaker.
The buffer continues to neutralize the acid. Its pH is 4.30. The deionized water drops to 1.38.
Repeat these steps eight more times. Add one milliliter of acid to each beaker and record
the change in pH until you've added a total of 10 milliliters. Let's look at the final results.
By adding acid we've dropped the pH of the water from 6.31 to 0.43,
but the buffer it held pretty steady and only dropped from 4.66 to 3.24.
Let's do the experiment again, but this time we'll add one milliliter of a base - six molar
sodium hydroxide. With two clean beakers add 100 milliliters of buffer to one and a hundred
milliliters of deionized water to the other. Just like before, take and record the initial pH.
Pipette one milliliter of our base, the sodium hydroxide, into each beaker. The buffer resists
the change in pH much better than the deionized water. The water's pH goes all the way to 12.55.
Continue adding one milliliter of base to each beaker and record the change in pH.
Eventually after adding seven milliliters of base,
the buffer can no longer keep up, but it maintains its stability far better than the water.
So there you have it...a quick demo of how buffers can help us maintain a stable pH.
You'll be using buffers to do just that in many of the activities in this course
and throughout your career. A lot of biotech products are very sensitive to
pH like vaccines and medicines, so storing them in a buffer during production or even
while they're transported to patients helps keep a stable pH. Thanks for watching.