what is a ph meter and why is ph meter calibation important?
What is a pH Meter and Why is pH Meter Calibration Important? – There are many methods used to measure pH levels, including litmus paper tests, indicator dyes and pH electrodes or meters, but pH meters are commonly used for most applications today. Let’s look at these devices in a little more detail, and understand why it’s important to perform equipment calibration for them.
pH is defined as an estimate of hydrogen ion activity in a substance, or simply how acidic ( a majority of hydrogen ions) or basic ( a majority of hydroxyl ions) it is. This characteristic is measured on a scale of 0-14, with 0 the most acidic and 14 the most basic. A pH of 7 is neutral, i.e. neither acidic nor basic.
While pH meters weren’t easily available a few decades ago, a huge variety of these instruments are now used for testing soil, water, food items, skin and more, by hobbyists and professionals alike. These devices are designed with two electrodes, one for sensing hydrogen ions and one for reference.
The sensing electrode detects changes in voltage based on hydrogen ion activity, while the reference electrode provides a constant voltage for comparison. The difference between the two voltages is displayed as a pH value by the meter, with higher voltages signaling acidic pH levels and lower voltages signaling basic.
To be certain of accurate and reliable measurements, you need to perform pH meter calibration. This is generally done by measuring different buffer solutions with standardized, well-defined values, and then adjusting the pH meter based on any deviations from the buffer’s known pH value.
Instrument calibration for pH meters is generally conducted in two ways:
1. Two-Point Calibration – In this method, a microprocessor-based pH meter calculates the real slope and offset error for the pH electrode. Based on this information, the meter’s mV/pH-equation is then adjusted to match the characteristics of the pH electrode in use.
The two calibration points bracket the range of values to be measured, so this method is also known as bracketing calibration. Readings that go past the calibrated range may be displayed with slight deviations from the true value, since they are extrapolated by the pH meter assuming linearity.
2. Multi-Point Calibration – With some pH meters, calibration can be performed for more than two pH values on both sides of the zero point, which in this case is pH 7.00.
Calibration at three or more pH values increases the measurement range of the device without recalibration being required.
Here’s why you need to perform pH meter calibration:
Changing Characteristics – Over time, aging and coating of pH electrodes can cause changes in their characteristics, and even the most stable electrodes cannot be produced with exactly the same characteristics. Calibration helps to match the current characteristics of the pH meter with the pH sensor in use, compensating for any difference between a pH electrode’s behavior in theory and reality.
Higher Accuracy – A minimum of three standards are required for a calibration curve, and a pH meter cannot be calibrated without a standardized buffer. If pH meter calibration has not been performed properly, the resulting measurements are likely to be inaccurate.
Reduced Drift – Measurement drift is a common issue with pH meters, as with any other instruments using electrodes. While drift from calibrated settings can’t be eliminated or prevented, regular equipment calibration helps you maintain accuracy in measurement results.
Sample Differences – Multiple samples of the same substance can have different characteristics, and calibrating pH meters against standardized buffers helps to prevent membrane-related issues such as differences in ionic strength.
Changes in pH affect the chemical nature of substances, and correct measurements are often crucial in industries such as agriculture, food and pharma. If you want to know more about the effects of changes in characteristics or why you need regular calibration services, contact us today!