Proper use of the pH sensor in the fermenter In use, the PH sensor is usually first added with a stainless steel protective sleeve and then inserted into the fermenter. Most PH sensors have a temperature compensation system. Since the contents of the electrode will change over time or by high temperature sterilization, calibration is required before each batch of fermentation sterilization operation, ie, calibration with standard pH buffer. Generally, the measurement range of the pH sensor is 0 to 14, the accuracy is ± (0.05 to 0.1), the response time is several seconds to several tens of seconds, and the sensitivity is 0.1. Fertigation is using your irrigator to fertilise the plants and soils as you water, which is the most efficient and advanced practice of fertilization. Aid of pressure system (or natural divide terrain), the soluble solid or liquid fertilizer, according to the soil nutrient content and crop fertilizer regularity and characteristics of species, with the fat of with irrigation water, through a controlled water supply pipeline system, supplying, the compatibility, water through the pipe and drop head form drip irrigation, uniform, regular, quantitative, infiltration area crop root growth and development, make the main root soil always stay loose and appropriate moisture content, at the same time according to different crop fertilizer characteristics, environment and soil nutrient content in soil; Crops in different growth phase water requirement, the different development stages of the fertilizer rule is the demand of design, the water and nutrient timing quantitative, provided directly in proportion to the crops. Greenhouse Drip Irrigation System Greenhouse Drip Irrigation System,Greenhouse Micro Irrigation System ,Plant Drip Irrigation JIANGSU SKYPLAN GREENHOUSE TECHNOLOGY CO.,LTD , http://www.spgreenhouse.com
(1) Calibration The sensor must be calibrated prior to use, which is the final step in sterilizing the fermentor. Calibration of the sensor is performed outside the fermentor and the pH electrode is immersed in a suitable container containing one or more standard buffers for calibration. These operations are preferably carried out at the operating temperature of the fermentor. The PH electrode needs to be connected to the pH meter used in the fermentation process. The calibration device of the PH meter can be adjusted according to the conventional pH meter calibration procedure. Since it is difficult or impossible to recalibrate the time during the fermentation process, it is best to fix the calibration control of the pH meter to avoid sporadic shifts in the experiment. Many commercial instruments provide some fixing screws.
(2) After sterilization calibration, the sensor should be inserted into the fermentor and sealed. When the fermenter is sterilized, the connection of the pH meter is generally removed (when sterilized by an autoclave), re-connected after sterilization, and the pH sensor starts to work. There are also experimental operators who use alcohol to sterilize the pH sensor separately (ie, do not put it in a sterilizer), mainly to extend the life of the sensor. The sensor is then immediately inserted and sealed in the can. It must be pointed out that this process may be contaminated. Although some reports claim that this step is used regularly in the study, there is no problem. Here's how: Place the sensor and add a suitable fitting to make the pH probe easy to install from the top of the fermenter, then place it in absolute alcohol for at least 1 hour. The probe and fittings must be very clean and the probe should be submerged above the fitting. Finally, the sensor should be quickly transferred to a pre-sterilized fermenter that is connected to the air supply system and the air has begun to flow.
(3) Calibration check The calibration may be offset during sterilization or use. For a good sensor, this offset will not exceed 0.2 units. However, some researchers still recommend calibration or recalibration after the fermenter has been sterilized. There are currently systems for larger fermenters that can be completely aseptically removed and partially inserted into calibration buffer for calibration. At the laboratory scale, it is necessary to completely remove the sensor and resterilize it using the chemical treatment described above. A good way to check a suspicious calibration in the laboratory is to aseptically sample the fermentation broth and measure the pH as soon as possible outside the fermenter for detection and reading. Because cells undergo continuous metabolism under changing conditions (eg, oxygen and matrix consumption in continuous culture), if the buffering performance of the medium is poor, the pH can change significantly within a few minutes, making it impossible to properly inspect the sensor. calibration.
1. Regular maintenance
The probe needs to be filled or filled with electrolyte from time to time. In fact, this is the electrolyte of the reference electrode, which is slowly lost through the porous plug. Manufacturers provide specialized fluids for their sensors, but many experimenters are willing to formulate their own: concentrated or saturated KCl solutions, sometimes adding certain solutes to increase viscosity (generally when the sensor is autoclaved in situ). In theory, the electrolyte level should be kept high enough to cause the static pressure to exceed the fermentation broth so that the fluid passing through the porous plug tends to flow from the sensor to the fermentation broth, but this is often difficult to achieve in practice. Although the electrolyte level is higher than the fermentation broth, the headspace pressure of the vented fermenter is generally slightly above atmospheric, which is caused by the resistance of the outlet gas filter and the outlet line. The headspace pressure of the probe electrolyte chamber is typically atmospheric during operation. A pressure differential of 103 Pa requires the probe to have a top height of 10 cm, which may be the maximum in practice, which is part of the reason for the fouling of the porous plug. If the pH probe has a sealed jacket, it may be beneficial to maintain a positive gauge pressure during the fermentation process.
2. Problems in use
In actual use, during PH actual use, the PH sensor may have the following problems: sensitivity/slope drop, slow response, noise signal and chemical damage.
(1) Sensitivity/rate skew There is a certain theoretical relationship between the pH and the electrode potential of the probe (see the Nernst equation described above). The new PH probe is close to its theoretical slope (ie, 59mv per PH unit at 25°C), but as the probe ages or breaks, the sensitivity decreases. Most PH meters or amplifiers can control and change the sensitivity (usually labeled as slope or sensitivity) that converts the voltage signal to a pH reading, which can be scaled by mv or temperature (because temperature is the only factor that theoretically affects the slope). It is worth noting that this is different from "buffer setting" or "zero control"
(2) Cleaning When the pH probe exhibits a response delay or a decrease in sensitivity, it needs to be cleaned. The main reason for the deterioration of the PH probe is that the material in the fermentation liquid contaminates the porous plug, and if the porous plug is contaminated, it turns from white to brown or black. To prevent contamination, the pH probe can be immersed in a 10 mmol.L-1 HCl solution so that the pH sensor is not damaged (this can also be used to routinely store the pH probe during the run interval). Sometimes adding pepsin helps remove protein precipitates. If HCl treatment has no effect, try the following two methods, although they have a certain risk of damaging the pH probe, but they also have some effect. Soak the pH probe in about 1% H 2 O 2 solution for about 1 to 2 hours; or gently mechanically clean the porous plug, that is, use a sharp blade to scrape off the deposit on the outer surface.
(3) The high impedance of the electrical interference meter and the amplifier circuit may cause some problems, which makes the PH probe sensitive to the noise caused by the induced voltage of the stray field entrance of other electrical equipment, for the two signals carried by the PH probe. The error response caused by a small current leakage between the terminals is also sensitive. Special shielded conductors and binding posts are available for this manufacturer of PH sensors or PH meters. If there is excessive noise, remove the PH probe wires from other wires to reduce noise. The agitator motor can be a source of interference, which can be checked by turning the motor off for a few seconds. The spike on the PH trace corresponds to the on or off of the heater circuit (the switch can be viewed by the lamp or judged by the sound of the relay switching of the heater control unit). Noise or inaccurate readings after autoclaving can reflect contamination of the terminals and wires caused by vapor condensation during sterilization.
(4) Preventing mechanical damage The pH probe is quite fragile and is easily damaged during the installation and cleaning of the fermenter. It is recommended to insert the PH probe at the end of the fermenter preparation (need to be calibrated here), and remove the PH probe first after use (under can). In many cases, the sensor is damaged because the top cover of the fermenter is lifted directly without removing the sensor. In order to avoid damage to the probe during storage during the run interval, an easy way is to place the sensor in a plastic cylinder with a dedicated solution. Select the appropriate cylinder size so that the wider part of the probe can also be placed. The ball detection area is suspended above the bottom (for example, a cotton can be inserted into the bottom of the cylinder), and the cylinder is preferably clamped.