pH Meter
What are they and why do we use them? What types are there?
A pH meter measures the pH of a liquid, in short: How acidic or basic it is. A lot of synthetic biology requires buffered solutions - solutions that maintain a consistent pH despite external variables. These are mixed from a weak acid and a strong conjugate base (or vice-versa). When mixing a buffered solution, you will absolutely need a well calibrated pH meter.
There are two general types of pH meter;
Portable - small pen-like device that has an onboard battery. These are much more convenient but less accurate unless you spend a lot of money.
Desktop - larger machine, plugged into the wall. Generally considered more accurate, but also significantly more expensive. A cheap desktop pH meter will probably perform worse than an expensive portable pH meter.
That said, perfect accuracy isn’t much needed for the mixing of buffered solutions - so this is an area where you can afford to be cheap. I’ve seen some excellent DIY pH meters, made from a few standard parts. If I ever make one of my own, I’ll include pictures here.
When do you use?
During protocols such as buffer mixing, or when attempting to make pH-specific media. Some researchers like to buffer their LB liquid media at pH 8, but I’ve never found this to make much of a difference.
How do you use?
Calibrate: Using the instructions in the manual, calibrate your pH meter with the three buffered solutions provided. When they run out, you can order more ‘pH calibration solution’ for a refill.
Hold the end of the meter fully submerged in the liquid and wait until the number on the readout steadies. As a quick refresher;
pH < 7 = Acidic
pH = 7 = Neutral
pH > 7 = Basic/Alkaline