A pH meter is a small type of testing equipment commonly found in laboratories. For the use and maintenance of the ph meter, most people will say that it is very simple and easy. But in fact, do you really know how to use, maintain, and maintain the ph meter? Do you want to make a small "?" “Sheng Aohua†has been focusing on the environmental water quality testing instrument industry for more than 20 years, providing many quality water quality monitoring solutions for new and old customers and friends. Customer satisfaction is our greatest reward and our pursuit. "Sheng Aohua" has a wide range of water quality testing instruments, including desktop, portable, handheld, push-button, touch-screen and so on. First of all, for the simple science popularization of "Sheng Aohua" independently developed two pH meters: desktop PHS-300, hand-held PHB-9. As shown below: Figure 1: Benchtop pH meter: PHS-300 ◇ Full touch screen benchtop pH meter, personalized touch button ◇Automatic identification of standard buffer function, three-point calibration ◇Automatic identification of temperature compensation Figure 2: Handheld pH Meter: PHB-9 ◇Backlit LCD display (can be turned off) ◇Shows pH, temperature or mV (ORP), temperature simultaneously ◇With manual temperature compensation, support two-point calibration, three-point calibration ◇Small shape, easy to carry, easy to operate The following focuses on this! This article mainly from three aspects: the principle, maintenance, common problems and solutions of the ph meter, for everyone to elaborate on all aspects of the pH meter. The principle of a pH meter By measuring the potential difference measured by the working battery composed of the electrode and the reference electrode in the solution, and using the linear relationship between the pH value of the solution to be tested and the potential of the working battery, and then converting the value into a pH unit value by the ammeter. Achieve the measurement. 2. Maintenance of pH meter 1. pH meter glass electrode storage When the pH meter is not used for a short period of time, it can be fully immersed in a saturated potassium chloride solution. However, if it is not used for a long time, it should be dried and should not be washed with washing liquid or other water-absorbing reagents. 2. pH glass electrode cleaning Contamination of the glass electrode bulb may lengthen the electrode response time. Decontaminate can be removed with CCl4 or soap, then immersed in distilled water for a day and night to continue use. When the pollution is serious, immerse in 5% HF solution for 10-20 minutes, rinse immediately with water, then immerse in 0.1N HCl solution for a day and night and continue to use. 3. Treatment of glass electrode aging The aging of the glass electrode is related to the gradual change of the rubber layer structure. The old electrode has a slow response, high membrane resistance, and low slope. Etching the outer layer with hydrofluoric acid often improves electrode performance. If this method is used to periodically remove the inner and outer layers, the life of the electrode is almost unlimited. 4. Reference electrode storage The best storage solution for the silver-silver chloride electrode is a saturated potassium chloride solution. The high concentration potassium chloride solution prevents the precipitation of silver chloride at the liquid junction and maintains the liquid junction in a working state. This method is also applicable to the storage of composite electrodes. Three. Common problems and solutions 1. For the same sample, the pH measured twice is different? A change in temperature or a chemical reaction in the sample itself causes a change in pH. Therefore, try to keep the temperature consistent and avoid chemical reactions. 2. The same sample, measured on two pH meters at the same time, the readings are inconsistent? Since the calibration conditions of the two pH meters are different (for example, corrections made at different times), the measured values ​​are different. Therefore, the pH meter should be calibrated at the same time with the same buffer, and then measured simultaneously. 3. Why is the buffer deteriorated within the validity period and cannot be used? The expiration date of the buffer refers to the shelf life in the unopened state of use. Once opened for use, the buffer is more susceptible to deterioration due to the action of various molds in the air. Note: The used buffer must not be returned to the original bottle! 4. How often does the electrode need to be calibrated? The calibration frequency of the electrode depends on the specific conditions of the electrode's use, maintenance, sample properties, and measurement accuracy. It is recommended to calibrate once a day, up to a maximum of one week. Replace the electrode and do not use it for a long time. It must be calibrated before use. 5. How to maintain the pH electrode? After using the electrode for a period of time, if the slope is low and the response speed is slow, try the following methods: 1 If the sample contains protein, the electrode film can be washed with a pepsin/hydrochloric acid wash. 2 If the measurement sample is an oily/organic liquid, it can be washed with acetone or ethanol. 3 If the electrode junction is found to be dirty and black, the thiol cleaning solution can be used to clean the junction. 4 Activate the electrode film, the activation method: the electrode regeneration solution is immersed for 30 seconds, and then immersed in a 3 mol/L KCl solution for 5 hours. 6. The sample temperature is 10 ° C. At this time, the meter shows the pH value at 10 ° C or 25 ° C? The pH meter shows the pH of the solution at the current temperature. If measured at 10 ° C, the meter shows the value of the solution at 10 ° C. If you need to obtain a pH of 25 ° C, the solution temperature must be raised / lowered to 25 ° C, and then Make measurements. The temperature compensation of the acidity meter refers to the effect of the compensation temperature on the pH electrode, but the pH value at any temperature cannot be compensated to 25 °C. 7. Why is the electrode displayed as 7.02 after being calibrated in a buffer of pH 7.00? At this time, the buffer temperature is about 20 °C. Since the pH of the buffer will vary slightly with temperature, 7.00 is only the value of the buffer at 25 ° C, and the buffer should be 7.02 at 20 ° C. The pH meter automatically compensates for the effect of temperature on the buffer to ensure measurement accuracy. 8. How long is the pH electrode life? The life of the pH electrode is related to the nature of the sample being measured, the temperature of the sample and the frequency of use, and maintenance. The pH electrode has a life of 1 to 2 years under normal use and proper maintenance. 9. Is the pH meter inaccurate? The pH meter is not accurate. The only reliable and simplest method is to use a pH standard buffer solution for verification. Take three pH standard buffer solutions: pH 6.86, pH 4.00, pH 9.18 (preferably freshly prepared and at the same temperature), position calibration at pH 6.86, slope calibration at pH 4.00, and then test pH 9. 18 See if the pH meter is accurate, and whether it is qualified or not. If the accuracy is not acceptable, it can be further judged whether there is a problem with the pH meter or a problem with the pH electrode. 10. Summary of the reasons for the digital instability of the pH meter: 1 Check if the electrode is damaged; 2 should be the electrode used for too long, first check to see if it is effective; 3 can try to soak the probe with 2.5mmoL / L KCL solution; 4 cleaning the glass ball, is it a long time, some organic matter is attached to it, resulting in insensitive reaction; 5 There is a chemical flat CO2+H2O→H++HCO3- in the water. Since the general pure water or surface water is weakly alkaline, the equilibrium will move in the positive reaction direction, so the pH will rise all the time; 6 Add a neutral salt (such as KCl) as an ionic strength modifier to the water sample to change the total ion intensity in the solution, increase the conductivity, and make the measurement fast and stable. The national standard GB/T6P04.3-93 of this method stipulates: “In order to reduce the influence of the liquid junction potential and quickly reach stability when measuring the water sample, a drop of neutral 0.1 mol/L KCl solution is added to each 50 mL water sample.†The method changed the ionic strength in the water sample, which caused the pH value to change to some extent, but it was experimentally proved that the change only changed the value of 0.01 pH, which is completely acceptable. However, when using this method, it must be noted that the added KCL solution should not contain any alkaline or acidic impurities. Therefore, the KCl reagent should be of high purity, and the water quality of the solution should be high purity neutral water quality. Lipstick Case,Color Changing Lip Gloss,Lip Gloss Gel,Lip Gloss For Kids Guangzhou Shishi Daily Chemical Co.,Ltd. , https://www.cosmeticok.com
