Step 1: Cleaning Fig. A: pH reading from a properly cleaned electrode in pH 7 solution. Fig. B: pH reading from a dirty electrode in pH 7 solution. pH 7 pH 7 Average: pH 6.5 pH 5.5 Fig. B pH 7 pH 7 pH 7 Average: pH 7 Fig. A Just because you can’t see contamination doesn’t mean it isn’t there. An electrode generates a voltage of the average hydrogen ion concentration from the surface area outside the pH bulb tip. Fig. A above shows that the clean electrode is submersed in pH 7 from all areas of the bulb surface. When an electrode becomes dirty from use or neglect, the contaminated surface contributes to a voltage offset based on the surface area exposed to buffer as seen in Fig. B. Now the pH meter is mistakenly reading pH 6.5 instead of the actual pH 7. Always clean your electrode before calibration. If a dirty electrode is used for calibration, all subsequent measurements will be in error. A dirty electrode can contaminate solutions. Always use fresh solutions with each calibration. Buffer solutions can be contaminated by dirty electrodes as in Fig. C. Always clean your electrode before each calibration and measurement, and always use fresh solutions. Contamination can take time to work its way around the beaker. If you notice fluctuations in your readings, it may be time to calibrate with fresh solutions. Fresh Every Time Hanna single-use sachets are a great way to ensure your solution is always fresh. Fig. D shows just how easy it is to tear open the packet and insert the electrode. These opaque sachets are also the ideal size for testers. pH Cleaning Procedure Hanna manufactures a full complement of cleaning solutions formulated to address general and specific cleaning needs. IMPORTANT: After performing any of the cleaning procedures, rinse the electrode thoroughly with purified water (Fig. E) and soak the electrode in HI70300 or HI80300 Storage Solution for at least 1 hour before taking measurements (Fig. F). General Cleaning Soak in Hanna HI7061 or HI8061 General Cleaning Solution for approximately 30 minutes to dissolve mineral deposits and other general coatings. Protein Coating Soak in Hanna HI7073 or HI8073 Protein Cleaning Solution for 15 minutes to enzymatically dissolve deposits from protein sources. Inorganic Soak Soak in Hanna HI7074 Inorganic Cleaning Solution for 15 minutes. This cleaner is especially effective at removal of precipitates caused by reaction with the silver in the filling solution that may form in a ceramic junction. Oil and Grease Rinse Oil and grease removal require the correct chemicals to solubilize the coating, but mild enough to leave the electrode unaffected. Use Hanna HI7077 or HI8077 Oil and Fat Cleaning Solution. Step 2: Calibration Calibration only counts when using fresh solutions and properly cleaned electrodes. A pH electrode that is properly manufactured and kept clean will retain its measuring integrity for a long time. As a result of many factors such as age, use, poor maintenance, or improper handling, any electrode will lose its integrity in time. Fig. C Fig D. Routine maintenance will ensure accurate readings while extending the life of your electrode. Fig E. 1 hour Fig F. Electrode Cleaning, Calibration and Maintenance 2 pH 2.160 | www.hannainst.com solutions
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