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The precision and the lifetime of the pH meter depends on the pH electrode. Sometimes, the pH measurement is inaccurate when using inappropriately. After a period of use, the membrane of the pH glass electrode may be block or be scratched, causing the potential to shift, and needed to be calibrated for each time of use. In addition, the pH glass electrode needs to be calibrated for the following situations:
pH value test is the measurement of the concentration of the activity of the hydrogen ion which lead to acid, base or neutral of the solution. pH test Using potentiometry to measure the pH value, pH glass electrode is constructed with the glass working electrode and the reference electrode. The glass working electrode is sensitive in potential toward pH value while the reference electrode provides a stable reference potential. By combining these two electrodes together and immersing into the solution, the potential output of the electrode is linear to the pH value at the consistent temperature. Because the situation mentioned above can cause bias of the linearity, the glass electrode needs to be calibrated with standard solution after using a period.
Both these two types of calibration need to start from pH 7 to make the zero potential calibration. Two-point type calibration is sufficient for most situation and three-point type calibration is for more precise measurement.
For precise pH measurement everyday or having no standard solution, there are calibration-free type pH electrode available. The principle of calibration-free pH measurement system is similar to pH glass electrode. By measuring the potential different, the concentration of the hydrogen ion can be measured and transfer to pH value via Nernst Equation. Another feature of calibration-free system is disposable, no cross-contamination for the sample. Through seriously controlling the process of auto manufacturing, the strip electrodes have been calibrated in the factory and the information of calibration is labelled on the package. User only needs to input the information to the pH meter for the first time and needs no calibration afterward. Moreover, strip electrode only needs micro-volume sample to perform the measurement due to its microfluidic design. Many experiments, which have limited amount of sample, can use directly without other procedure, especially in bio-experiment. And the sample will not be contaminated by other sample due to the disposable design. For an outdoor experiment, only the meter and the strip are needed, which is more convenient to operate without carrying the standard solution and other component.
There are different chemical reagents, like Methyl red, change at the range of pH 4.2 (red) – pH 6.2 (yellow), Bromocresol green, change at the range of pH 3.6 (yellow) – pH 5.4 (green), and Thymol blue, change at the range of pH 6.7 (yellow) – pH 7.5 (blue), have different color at different pH range. Immersing white paper into the solution that have a proper ratio of these reagents, the pH test paper is produced. The pH test paper is more convenient to use and the price is lower compare to the glass electrode. But the pH test paper use visualize color to measure the pH which is not accurate because of the personal error. And pH test paper can not be used to constantly monitor and record pH value change .
The pH glass electrode performs an accurate measurement. Because of the character of the glass electrode, it needs to be calibrated with pH 4, 7, 10 standard solution every time before use. The calibration, which takes 5 – 10 minutes, is complicate and needs to be operated with cautions. To maintain the glass electrode, the electrode should be cleaned and dried tenderly and kept in the stock solution after using. Any incorrect operatione can cause the glass membrane being scratched and damaged . In addition, the maintenance and preservation of the glass electrode also has many points need to be noticed. You should avoide the pH glass electrode membrane from dryness. So the pH glass electrode needs to be properly stored in preserving fluid, otherwise it will affect the accuracy and precision of pH test. According to all the procedures mentioned above, the pH glass electrode should be used carfully with the person who has been professionally trained . Moreover, the price of pH glass electrode is between 100 – 1,000 USD, which is higher than other pH measurement method.
The Humming Probe pH measurement system provides by UltraE Co., Ltd. gives user a convenient way to measure and monitor pH value. User only needs to take out the strip electrode from the vial and just few procedures to measure the pH value without calibration and maintaining the electrode. The principle of calibration-free pH measurement system is similar to pH glass electrode. By measuring the potential different, the concentration of the hydrogen ion can be measured and transfer to pH value via Nernst Equation. The feature of calibration-free system is disposable, no cross-contamination for the sample. Through seriously controlling the process of auto manufacturing, the strip electrode is calibrated within the factory and the information of calibration is labelled on the package. User only needs to input the information via the QR code to the meter for the first time and needs no calibration afterward. Moreover, strip electrode only needs micro-volume sample to perform the measurement due to its microfluidic design. Many experiments, which have limited amount of sample, can use directly without other procedure, especially in bio-experiment. And the sample will not be contaminated by other sample due to the disposable design. For an outdoor experiment, only the meter and the strip are needed, which is more convenient to operate without carrying the standard solution and other component. Moreover, the price of the stripe is around 1 USD, much lower than the glass electrode.
| Glass electrode | HUMING PROBE | Test Paper | ||
|---|---|---|---|---|
Product / item |  |  |  | |
| Operability | ||||
| Operability | Difficult | Easy | Easy | |
| Accuracy | ||||
| Accuracy | Heigh | Heigh | Low | |
| calibration | ||||
| calibration | Needed | No Needed | No Needed | |
| Sample volume | ||||
| Sample volume | More(5~10 mL) | Less(1~20 μL) | Less(50~100 mL) | |
| Maintenance | ||||
| Maintenance | Difficult | Easy | Easy | |
| Price | ||||
| Price | Height | Low | Low | |
| Cross-contamination | ||||
| Cross-contamination | Possible | Dispossible | Dispossible | |
