pH measurement is a standard application in almost any lab. To help make your job a little easier, below is a list of typical questions asked by you, our customers, in the area of pH. We have, of course, included the answers. If you have additional or more detailed questions about pH measurement or any other laboratory and/or instrument application, we do have trained engineers and technicians on staff ready to take your call and help you with your work. For more information, please call our Customer Service Department at 1-800-528-5114.
Question: If I order a pH meter, what accessories do I need to use with it?
You need a pH electrode and at least two pH buffers, one at pH 7 and your other buffer at pH 4 or 10. Optional accessories that will prolong life of your electrode include: storage solution, soaker bottle, cleaning solution.
Question: How do I measure pH?
Markson offers 2 ways to test for pH:
1. pH strips or indicating paper
2. pH meter and electrodes
Question: Do I need a portable meter or a bench meter?
If you will be transporting the meter from place to place, a battery operated portable meter would be the choice. If the meter will be stationary, as in a lab, choose a bench-top meter.
Question: How should I store my electrode?
The best solution for storage is 4M KCL. pH 4 buffer, pH 7 buffer, or tap water will also work as storage solution. Caution: never store your electrode in distilled water.
Question: How often do I need to calibrate my pH meter?
Before each time you use it or each set of uses.
Question: What is the difference between automatic temperature compensation and manual temperature compensation?
If a meter has manual temperature compensation, it means a separate device is necessary to record the temperature of the buffers and sample solutions. That temperature is then set on the meter temperature dial, thus "manually compensating" for temperature.
A meter with automatic temperature compensation will internally compensate for temperature as long as a temperature probes is connected to the meter. A meter with ATC is much faster to use and ideal when multiple samples are being measured.
Question: Should I stir my sample during pH measurement?
Yes. There are two main advantages to slowly stirring or gently agitating the sample during a pH measurement. First, the increased flow of the sample across the electrode results in a faster response time. Second, the solution is properly homogenated so no areas of increased or decreased pH exist.
Question: When is a pH reading stabilized?
It is difficult to know the exact time to take a pH reading. In general, one minute is required to obtain a stable reading. If a reading is taking an exceptionally long time to stabilize, this can indicate several conditions: a clogged electrode junction, a non-homogeneous solution, a troublesome sample with low ionic strength, or a non-aqueous sample.
Question: How do I take a pH measurement in soil?
Prepare the sample by combining a 5 g soil sample with 5 g of distilled water, mixing thoroughly, and allowing the mixture to settle for 10 minutes. Carefully insert probe so bulb is in the soil part and the junction is in the supernatant. Allow reading to stabilize.
Question: Can I measure the pH of a gas?
The only way to measure the pH of gas is to dissolve it into distilled water and measure the mixture.
Question: Should I use a combination electrode or an electrode pair?
A combination electrode is the most popular type of electrode and is easier to use. It is ideal for most field and lab applications. Electrode pairs are primarily used as ions selective electrodes of for use when measuring colloidal suspensions. When measuring high purity water, a dedicated electrode pair with a special glass bulb is recommended.
Question: What is the difference between a combination electrode and a sensing electrode with a reference cell?
A combination electrode is more convenient and requires a smaller sample container and volume. The sensing electrode with reference cell combination allows you to select the reference cell most compatible with your solution. You can select the double junction, calomel or ROSS Sure Flow half-cell. Most likely, you will get a longer lasting electrode from this combination and can replace each cell individually.
Question: Should I use a double junction or single junction electrode?
Single junction electrodes are the most commonly used electrodes. Double junction electrodes should be used for solutions containing proteins, sulfides, tris buffers or heavy metal ions.
Question: Is a glass body electrode or epoxy body electrode more appropriate?
Glass bodies electrodes can withstand higher temperatures, have minimal sample carry over because of their design, and can withstand highly corrosive material and organic and solvents. Glass electrodes are mainly used in laboratory situations. Epoxy-body electrodes are more rugged than glass electrodes and are the best choice for field, plant, and industrial applications.
Question: When do you use a half-cell?
A half-cell should be used when you are measuring a pressurized flow in a stream or pipe. The reference half-cell would be mounted upstream, the measuring electrode would be mounted down stream.
Question: How can you unclog a pH electrode? How can you restore a refillable pH electrode?
First you should check the interior wire. If corrosion is evident, replace the electrode. If not, then soak the electrode in KCL solution at 50 degrees C for 2 to 4 hours. Restore a refillable electrode by soaking it in pH 4 buffer after rinsing out the refill chamber with distilled water and refilling with the proper solution.
Question: How far can my pH electrode be from my meter? What if it is too far?
100 feet is the maximum distance an electrode can be from a pH meter. If the distance is greater, you will need a pre-amp or an in-line amp. Or, you can purchase an industrial electrode with a built-in pre-amp.