Dissolved oxygen refers to molecular oxygen dissolved in water or liquid phase, and it is represented by DO. Dissolved oxygen analyzer is an instrument used to measure molecular oxygen dissolved in water or liquid phase. It is widely used in environmental monitoring, aquaculture, sewage treatment and other departments. Frequent and correct maintenance of the dissolved oxygen analyzer is essential to ensure the measurement accuracy of the instrument and to extend the life of the instrument, especially the electrode. Pay attention to the following items in the daily maintenance and use of the dissolved oxygen analyzer.
(1) Calibrate once a day before use, you can use the water saturated air method.
(2) The temperature during calibration and measurement should be as consistent as possible, and the difference should not be too large, thereby affecting the accuracy of the measurement.
(3) The dissolved oxygen analyzer should regularly replace the dissolved oxygen membrane and electrolyte, and regularly clean and regenerate the electrode. In the process of use, the dissolved oxygen membrane will be contaminated, causing the electrode reading to drop and the response time to slow down, especially under the conditions of sewage measurement, the situation is more serious. In this case, the dissolved oxygen membrane should be cleaned and replaced frequently. The dissolved oxygen membrane can be cleaned with clean water, or use cotton dipped in alcohol to gently wipe off the dirt.
If there is any leakage during the measurement, the test liquid will immerse into the electrode and contaminate the electrode. Therefore, the dissolved oxygen membrane should be checked frequently. If the dissolved oxygen membrane is found to be broken, the dissolved oxygen membrane and electrolyte should be replaced in time. During the use of the instrument, if the reading of the instrument is found to be abnormal (for example, the reading is very unstable after turning on or the reading is not stable from high to low), the electrode should be taken out for inspection in time, and the dissolved oxygen membrane and electrolyte should be replaced.
The electrolyte must be replaced with a new dissolved oxygen membrane in time when the electrolyte is dry.
When replacing the dissolved oxygen membrane, first rinse off the old and remaining electrolyte with deionized water or distilled water, add 2, 3 drops of new electrolyte and spin dry. Then drip the new electrolyte* and the liquid surface will bulge, press on the dissolved oxygen film without leaving bubbles, and the dissolved oxygen film must be flat and not wrinkled. After replacing the dissolved oxygen membrane, it should be placed overnight, at least one hour to allow the membrane and electrolyte to balance and ensure the stability of the instrument. After the electrode is used for a long time, the silver anode turns dark or completely black. This is mainly due to the precipitation of silver chloride on the anode, which requires regeneration of the electrode. Pour out the electrolyte, turn the electrode upside down, and inject concentrated ammonium hydroxide (aqueous ammonia) into the electrode cavity until the anode turns silver gray. Pour out the ammonia solution, clean the electrode cavity with deionized water or distilled water. The cleaned electrode should not smell of ammonia, and then install the electrode. The electrode sensitivity of the dissolved oxygen analyzer is affected by the flow rate. Therefore, when measuring dissolved oxygen, the most taboo is to measure in a static state, that is, there should be relative movement between the measured water sample and the electrode.
Motor stirring or electromagnetic stirring can be used in the laboratory. The electrode can be gently shaken during on-site measurement, but attention should be paid to avoid oxygenating the water sample with air, especially when measuring hypoxic water samples. Dissolved oxygen online analyzer, it is best to recalibrate zero oxygen after it is put into operation for about half a month, because the residual current of the oxygen electrode will decrease after working in the trace dissolved oxygen water sample for a period of time, and it will be close to its true value. The dissolved oxygen analyzer can not be stored dry when not in use, because the electrolyte water vapor in the chamber will evaporate when the oxygen electrode is dry, causing bubbles inside the electrode, which affects the performance of the electrode, especially the residual current performance of the electrode.
The dissolved oxygen analyzer should be sealed and stored in water when not in use for the oxygen electrode for trace measurement. For the galvanic cell type electrode, it should be stored in a short circuit, so that the zero oxygen calibration can be carried out quickly and the reading can quickly return to zero. Pay attention to the influence of dry air. N2, O2, NH3, CO2, H2S and other gases can diffuse and penetrate the film. N2 is an inert gas and does not react, CO2 gas will make the electrolyte more acidic, and NH3 gas will make the electrolyte more alkaline. On the other hand, NH3 can form Ag+(NH3) 2 with Ag+, thus affecting the measurement. If the sensor is exposed to CO2 gas for a long time, CO2 gas will cause the electrolyte pH value to drift towards acidity and cause the reading to increase. The hydrogen sulfide gas will poison the oxygen electrode and affect the accuracy of the dissolved oxygen analyzer measurement results and the service life of the oxygen electrode. Therefore, the contact of the oxygen electrode to these gases should be minimized.