pH electrode daily maintenance for basic fermentation knowledge

The fermentation process is usually performed using a compound pH electrode directly inserted into the vessel fermentation broth for real-time monitoring of pH. The sterilization operation at high pressure and high temperature and the physical and chemical properties of the fermentation liquid will affect the pH electrode measurement, so the correct method of use and daily maintenance is especially critical.

# 1
Ready to install and use

1. When opening the package, carefully check whether there is mechanical damage to the PH sensitive membrane glass, diaphragm (plain fired ceramic core) and vitreous body of the electrode.
2. Remove the drip set and clean the top of the electrode with pure water, and then gently wipe dry with wet paper towel or absorbent paper. Be careful not to rub the PH sensitive membrane to increase response time.
3. Move the pH electrode to the vertical position to prevent bubbles in the memory of the PH-sensitive membrane glass bulb. If no wave body is filled or there are bubbles, gently shake the electrode to fill the bulb with liquid until there are no bubbles.
4. The electrode can be soaked in acid buffer (pH4.01) for several minutes before use, rinse the glass bulb part with pure water, and then gently blot the glass bulb part with absorbent paper, and then in neutral buffer (pH6.86 or 7.00 etc.) for a few minutes to activate the electrode before starting the calibration.

# 2
pH electrode two-point calibration operation

The pH electrode was soaked in standard buffer for 10min, and the first point calibration and the second point calibration of pH electrode were carried out successively after the determination value was stabilized for 1min.

Take the HOLVES fermenter as an example:

1. Before calibration, select parameters according to the buffer light type:
   ● [GB] refers to the use of the view in accordance with GB/T 27501-2011 standard buffer, generally used several buffer pH values of 4.00, 6.86 and 9.18. Its corresponding "stability", that is, the uncertainty of buffer is usually selected, ±0.02pH
   ● Holves generally uses METTLER TOLEDO InPro3030 series pH electrodes. The common number IMT9 corresponds to its brand of buffer solution, and the buffer wave pH value is 401, 7.00 and 9.21. The "stability" should be selected according to the type of buffer used.
2. Connect the electrode, rinse the electrode with pure water, and then gently blot the water on the probe with absorbent paper.
3. Partially immerse the glass bulb in the first buffer (e.g.: pH =401) (the diaphragm should be completely immersed in the suitizer). After the standard value is stable (30 seconds to 60 seconds), click the first point to confirm, then the first point calibration is finished.
4. Remove the electrode from the first buffer and rinse the electrode with pure water. After rinsing, gently blot the water on the probe with absorbent paper.
5. Put the glass bulb is partially submerged in the second flush solution (e.g.: pH=9.18)(the diaphragm should be completely immersed in the buffer). After the standard value is stable (30 seconds to 60 seconds), click the second point to confirm. The second point calibration is finished, and wait for use (not too long).

# 3
Precautions for electrode calibration

1. Please pay attention to the use of fresh buffer during calibration.
2. place the electrode in buffer for 1min before the subsequent operation.
3. After rinsing the electrode, only soft absorbent paper can be used to blot the water. Do not rub pH sensitive membrane.
4. Electrode calibration cycle according to different use environment and accuracy requirements, please determine the appropriate calibration cycle on the premise of ensuring accuracy.
5. Due to the Ph electrode probe is extremely fragile, so do not knock in the process in use.

# 4
pH electrode performance test

The pH electrode method is based on the principle of Nernst equation. The electromotive force of the electrode has a linear relationship with the pH value. Generally, two different pH buffer are used for calibration. To determine the slope of the curve. The commonly referred to as the pH electrode response slope, refers to the pH electrode used to convert the millivolt (mV) signal into pH value, it is measured by different buffer voltage difference, divided by the buffer difference value. This slope is an important indicator to determine whether the life of the plate is exhausted.

It should be noted that because the oblique home is proportional to the temperature star. When the temperature of the solution occurs. According to the Nernst equation, the AE of the solution will vary linearly with temperature T. The electrode is changed according to the detected solution electromotive force energy. It is calculated as a pH value, so temperature compensation must be performed to offset the effect of temperature on the measurement results.

The so-called temperature compensation is to convert the slope of the electrode at the calibrated temperature (generally 25°C) to the slope at the current temperature according to Nernst formula, so as to obtain the correct pH value at the current temperature. It is mainly used to correct the deviation caused by the difference between the temperature of standard sample and the actual sample solution during calibration.

HOLVES products can measure the current liquid temperature through the temperature electrode of the device, and then calculate the pH value through the software to display the temperature compensation. So, whether it's calibration or performance testing. It is necessary to ensure that the temperature electrode of the device is in working condition.

Specific operation method of slope test:

1. Clean the electrode after two points calibration with pure water, and dry the well with soft absorbent paper.
2. Adjust route parameters and stability according to the method used in the calibration above. The following takes MT standard as an example.
3. First, the pH-7.00 buffer was used to measure the zero point, and the MV value was read out on the display screen. The pH electrode zero of HOLVES standard configuration is within 6.5~7.5 fan, and the installed electrode is normal.
4. After cleaning the electrode, insert it into the standard buffer solution of pH=4.01 (denoted as pH1), read mV value (denoted as mV1) on the display screen.
5. After cleaning the electrode, insert it into the standard buffer solution with pH=9.21 (denoted as pH2), and read mV value (denoted as mV2) on the display screen.
6. Calculate the slope of the electrode, i.e. (mV1-mV2)/(pH1-pH2).
7. According to Nernst equation, the ideal slope is 59mV/pH in the ideal state (25°C). That is, for every change in pH of the solution, the electrode generates a potential change of 59mv. The slope should be around 59mV/pH with ideal correction. If the slope is less than 53mV/pH or greater than 63mV/pH, replace the pH electrode with a new one. So when the correction the results are credible for positive slopes in the 53-63mV/pH range.

HOLVES series fermenter can directly read out the voltage signal of the liquid measured by the electrode. In addition, if the electrode is faulty or incorrectly installed or used, the red message "Electrode is unavailable" will pop up at the bottom of the pH calibration interface, so that customers can know the use status of the electrode.

# 5
Cleaning of electrode

1. Generally polluted water, 0.1mol/L NaOH or 0.1mol/L HCl, clean the electrode for several minutes.
2. Grease or organic contamination clean the electrode with acetone or ethanol for a few seconds.
3. Sulfide contamination (blackening of the diaphragm) is treated with sulfuric acid/HCl, and the glass bulb is partially immersed in the solution (the diaphragm should be submerged in the solution) until the diaphragm is colorless (at least 1 hour), and then soaked in 3mol/L At least 12 hours in KCI, fully flushed wells can be used after recalibration.
4. Protein contamination (yellowing of diaphragm) Treat with gastrin/HCl, place glass bulb part in solution, make sure the membrane is submerged in solution (at least 1 hour), then rinse with distilled water, recalibrate.

# 6
Preservation of electrode

1. After the end of each production cycle. Rinse the electrode head and diaphragm carefully with deionized water. Never dry out the measuring solution on these parts.
2. Electrodes should not be stored in steam road water. When not used for a long time, it should be fully immersed in 3mol/L KCI or 9816 /viscolytTM electrolyte together with the electrode head and diaphragm.
3. The electrode can not be dry for a long time, can not be stored on the surface with dry medium. If the electrode has been dried for several days due to an error, soak it in the normal storage electrolyte for several hours before use.
4. Always check the connector for signs of moisture. If necessary, wash thoroughly with deionized water or alcohol, then dry it carefully.