Test strips or test strips for measuring pH are inexpensive and easy to use. So, why use a pH meter? pH meters are more expensive and last longer?
1. Resolution
Resolution refers to the smallest measurable change in the quantity being measured. For pH strips or digital pH meters, this refers to the interval at which readings are given. For most pH meters, the resolution is at least 0.1 pH units, and resolutions are usually 0.01 and 0.001 units.
For test strips, the resolution is much lower. Typical pH test strips covering a wide pH range have color intervals of 0.5 or 1.0 pH units. Special pH test strips that cover a narrow range have color scales down to 0.2-0.4 pH units. It is possible to interpolate between colors, but even the lowest resolution pH meter will usually have higher resolution than the highest resolution pH bar.
2. Accuracy
Precision refers to the repeatability of measurements. That is, as measurements are repeatedly made, more accurate measurement techniques will produce measurements that are closer to each other. Since the resolution forms the upper limit of accuracy, low-resolution measurement technologies such as test strips are less precise than high-resolution technologies such as pH meters. Although higher resolution does not necessarily mean greater accuracy, pH meters are generally more accurate than pH strips.
Precision refers to the uncertainty in a measurement, so a more precise technique will produce a measurement with less uncertainty. Accurate measurement techniques will produce measurements that are close to true values. In terms of accuracy, test strips have lower accuracy compared to pH meters because of their relatively low resolution.
In conclusion, pH meters are usually more accurate than test strips.
3. Objectivity and consistency
As the test strip is used, it changes color and is compared to the color chart. The problem with this is that different people see colors differently and may tend to interpret color comparisons differently. So two different people may report two different pH values when shown the same test strip. Besides that, the colors look different under different lighting conditions. Unless the lighting conditions are consistent, it may increase the uncertainty of the test strip measurement.
Also, the interpretation of test strips requires some judgment, especially when it comes to interpolating between scales. For example, if it is not clear which color on the chart is appropriate for the test strip, it is a matter of deciding whether to choose one color or report another intermediate value. Therefore, individual operators may not be completely consistent in making a measurement-to-measurement judgment. Even the same operator may report different pH values at different times, even if the color does not change.
The results of the test strips can also vary due to the way the test strips are processed. For example, the length of time the strip was exposed to the solution, how the strip was handled after it was removed from the solution, and the length of time between removing the strip and comparing the colors can all affect the final result. If all these conditions are inconsistent, some other variation may appear in the results.
The subjectivity of the test strip can be partially removed by scanning the test strip and analyzing the color by a computer, but this needs to be done with care to ensure consistent user handling and scanning/lighting conditions. Digital pH meters, on the other hand, produce a well-defined digital output, and the measurement protocol for using a pH meter is relatively easy to keep consistent.
4. Shelf life
The reagents contained in the test strips will deteriorate over time. A set of test strips will remain in good condition for about a year if stored properly under satisfactory conditions. However, exposure to moisture, sunlight, and high or low temperatures will tend to degrade the reagents in the test strips, affecting their performance. Degraded test strips may become unacceptable.
That said, pH meters also need attention. pH electrodes require proper care and storage, and the calibration solutions themselves have a limited shelf life.
5. Continuous measurement
In some applications, such as acid-base titrations, it is necessary to monitor the pH over time in order to detect or document changes. Among other limitations, test strips are less suitable for this than pH meters because each test strip can only be used for one measurement. Digital pH meters, on the other hand, can report pH continuously and even log measurements automatically.
in conclusion
In applications where lower resolution and accuracy are acceptable, pH test strips may be a good choice because they are inexpensive and easy to use, as long as the strips are relatively new and kept in good condition.
Where moderate to high levels of resolution and accuracy are required, pH meters are likely to be good choices, even though they require more upfront investment and more skill to use. When choosing a measurement technique, the potential for error should be taken into account: inaccurate measurements, such as adding too much material to correct pH, suboptimal growing conditions, or loss of final product quality.
