The Method for Cutting Down on PH Meter Measurement Error
The best way to reduce the measurement error of pH meter | acidity meter. The pH meter is one of the common electrochemical analysis instruments in the laboratory. However, users are prone to large errors and failures during use. Anhui Secco Environmental Technology Co., Ltd. elaborates on the problems encountered in the verification as follows. I hope that everyone will collect such articles well, so that the error in future measurements can be smaller and safer.
1 Inspection of pH meter
When the laboratory personnel measure the pH value of the solution with an acidity meter, if they do not trust the measured results, they can use the following methods to judge, that is, to measure one or two pHs standard solutions. If the error of the measured pHs standard solution is very small, it shows that the measurement result of the acidity meter is reliable. Conversely, if the measured pHs standard solution has a large error, it means that some of the electric meter, electrode and pHs standard solution in the pH meter|acidity meter have problems, and check them one by one according to the following methods.
(1) For the electrometer, except for obvious faults, the problems that should be paid attention to: first, the temperature compensator must be placed correctly, and the knob must not be loose; second, the pH meter with slope correction, when measuring the solution by one-point positioning method , the slope should be placed at 100% position; Third, pay attention to whether the glass electrode jack is in good contact.
(2) For the pH glass electrode in the first electrode, check whether the silver-silver chloride internal reference electrode is immersed in the solution in the glass electrode. For the calomel electrode, attention should be paid to whether there are air bubbles in the tube, whether the salt bridge is blocked, and whether the calomel electrode contact sheet is oxidized. It can also be judged by replacing the good electrodes one by one.
(3) For the pHs standard solution, it should be re-prepared, and the calibrated acidity meter can also be used to measure the error of the standard solution. In general, the possibility of large errors in the pHs standard solution is small.
2 Instrument maintenance
Frequent and correct use and maintenance of the instrument can ensure the normal and reliable use of the instrument, especially the instrument such as the pH meter, which has a high input impedance, and the use environment requires frequent contact with chemicals, so reasonable maintenance is required .
(1) The input terminal (measuring electrode socket 6) of the instrument must be kept dry and clean. When the instrument is not in use, insert the Q9 short-circuit plug into the socket to prevent dust and water vapor from entering.
(2) The electrode converter (optional) is specially used for matching with other electrodes, and it should be protected from moisture and dust at ordinary times.
(3) When measuring, the lead wire of the electrode should be kept still, otherwise it will cause unstable measurement.
(4) The power supply used by the instrument should be well grounded.
(5) The instrument uses a MOS integrated circuit, so the circuit iron should be well grounded during maintenance.
(6) When calibrating the instrument with a buffer solution, the reliability of the buffer solution must be ensured, and the wrong buffer solution cannot be mixed, otherwise it will cause errors in the measurement results.
3 Precautions for electrode use and maintenance
(1) The electrode must be calibrated with a standard buffer solution of known pH value before measurement, and the closer the pH value is to the measured pH value, the better.
(2) Before the next operation after each calibration and measurement, the electrode should be fully cleaned with distilled water or deionized water, and then cleaned once with the measured solution.
(3) After removing the electrode sheath, avoid contacting the sensitive glass bubble of the electrode with hard objects, because any damage or rubbing will invalidate the electrode.
(4) After the measurement, put the electrode protective cover on in time, and put a small amount of external reference replenishment solution in the electrode cover to keep the electrode bulb moist, and do not soak in distilled water.
(5) The supplementary liquid for the external reference of the composite electrode is 3mol/L potassium chloride solution. The supplementary liquid can be added from the small hole on the upper end of the electrode. When the composite electrode is not in use, pull up the rubber cover to prevent the supplementary liquid from drying up.
(6) The leading end of the electrode must be kept clean to prevent short circuit at both ends of the output, otherwise it will cause measurement inaccuracy or failure.
(7) The electrode should be matched with a pH meter with high input impedance (≥1012Ω) to maintain good characteristics.
(8) The electrode should avoid long-term immersion in distilled water, protein solution and acidic fluoride solution.
(9) Avoid contacting the electrode with silicone oil.
(10) After long-term use of the electrode, if the slope is found to decrease slightly, the lower end can be soaked in 4% HF (hydrogen acid) for 3 to 5 s, washed with distilled water, and then soaked in 0.11mol/L hydrochloric acid solution , to restore it.
(11) If the solution to be tested contains special technology that is easy to contaminate the sensitive bulb or block the junction of the solution to passivate the pole, the slope will decrease and the display will be inaccurate. If this phenomenon occurs, it should be cleaned with an appropriate solution according to the nature of the pollutant to renew the electrode.
