The regulations for ion selective electrodes cover key steps such as electrode preparation, installation and connection, pretreatment, calibration, sample measurement, electrode maintenance, and troubleshooting, ensuring the accuracy of measurement results and the long-term reliability of electrodes. The following is a detailed introduction to the protocol for ion selective electrodes:
1、 Electrode preparation and inspection
Appearance inspection: Before use, the ion selective electrode needs to be visually inspected to ensure that the electrode surface is free of cracks and contamination. At the same time, check whether the filling liquid inside the electrode is sufficient. If it is insufficient, it needs to be replenished.
Electrode activation: Soak the electrode in deionized water for several hours to activate the electrode and clean the surface. During the soaking process, the electrode can be gently stirred or shaken to accelerate the activation process.
2、 Electrode installation and connection
Electrode socket selection: Choose the appropriate electrode socket based on the type of electrode. For example, the ELIT ion selective electrode needs to be inserted into the ELIT electrode combination socket and used together with a suitable reference electrode.
Electrode connection: Fix the electrode socket on a standard electrode bracket with adjustable extension range, and connect the wire with BNC interface to the BNC socket of the ion analyzer or pH/millivolt/ion meter.
3、 Electrode pretreatment
Soak pretreatment: Soak the electrode in a suitable ionic solution (usually 1000ppm, but not strictly specified, within the range of 500 to 5000ppm is convenient), soak for at least 5 minutes (stirring should be done from time to time during the soaking process) or soak until a stable reading is obtained.
Repeated rinsing: In order to obtain high-precision results, it is recommended to repeat the steps of removing the electrode, cleaning, drying, and immersing it in the solution until a difference of 1mV is maintained between three consecutive readings to ensure that the electrode receives appropriate rinsing and pretreatment.
4、 Electrode calibration
Standard solution preparation: Prepare at least two standard solutions with concentrations within the estimated concentration range of the sample to be tested (such as 1 and 10 ppm, or 10 and 100 ppm, or 100 and 500 ppm).
Measure standard solutions: Insert electrodes into these standard solutions in sequence and record the electromotive force values at each concentration. Draw the E-logC standard curve based on the Nernst equation, and determine the actual slope and detection limit of the electrode from the curve.
5、 Sample measurement
Sample pretreatment: Proper pretreatment of the sample is carried out based on its properties and analytical requirements. For example, for samples containing suspended solids, filtration or centrifugation is required; For samples with complex matrices, dilution or extraction may be necessary.
Sample measurement: Pour the pre treated sample solution into a beaker and place it in a stirrer. Insert the ion selective electrode and reference electrode into the sample solution, and turn on the electromagnetic stirrer for stirring. After the reading stabilizes, record the electromotive force value. To improve the accuracy of the measurement, multiple measurements can be taken and the average value taken.
6、 Electrode maintenance and upkeep
Electrode cleaning: After the measurement is completed, the electrode should be cleaned promptly. Rinse the electrode tip and opening with deionized water to prevent contamination of the ion selective electrode, which may affect its performance and lifespan.
Electrode storage: The electrode should be stored in a dry and cool place to avoid prolonged exposure to air or immersion in solution. For electrodes that are not used for a long time, they can be soaked in appropriate filling solution and covered with electrode protection caps.
7、 Precautions and troubleshooting
Avoid interference: Ion selective electrodes have varying degrees of interference with certain ions. Therefore, it is necessary to avoid the presence of these interfering substances during the measurement process, or to remove them through preprocessing methods.
Temperature compensation: Due to the significant influence of temperature on the response signal of the electrode, temperature compensation is required during the measurement process. Most ion meters have temperature compensation function, which can set the temperature value of the sample before measurement, and the instrument will automatically correct the measurement results based on temperature changes.
Troubleshooting: If there are issues such as unstable signals or longer response times during the measurement process, it may be a problem with the electrode or reference electrode. At this time, it is necessary to check whether the electrolyte is sufficient, whether the electrode cable is correctly inserted and screwed on, whether the electrode surface is damaged, etc., and take corresponding measures according to the specific situation.