Potentiometric dissolution assay for lead
Potentiometric dissolution assay for lead
This experiment is from the official website of College of Chemistry, Qingdao University of Science and Technology.
Operation method
Potentiometric dissolution assay for lead
Principle
The potentiodynamic dissolution method is divided into two processes: enrichment and dissolution. Enrichment process: The ions to be measured are first electrolyzed and enriched on the electrode at a certain potential to produce amalgam. Dissolution process: After electrolytic enrichment, disconnect the constant current circuit. With the oxidizing effect of the oxidizing agent, the amalgamated metal on the surface of the electrode is oxidized into ions, which enter into the solution, i.e. the dissolution process. The change curve of the working electrode was recorded at the same time. In this experiment, lead was enriched by electrolysis at -1.0 V. After enrichment, the constant-current power supply was disconnected, and oxygen was used as an oxidizing agent to dissolve lead. At the time of dissolution, the electrode potential was constant. The type and concentration of the oxidizing agent, the electrolytic potential, the electrolytic enrichment time and the electrode rotation speed were maintained under the same experimental conditions. The dissolution time is proportional to the concentration of Pb2+ in the solution. This is the basis of the potentiodynamic dissolution analysis method.
Materials and Instruments
DPSA-1 Miniature Potentiometric Dissolution Analyzer Model MP-1 Dissolution Analyzer Glassy Carbon Pre-Plated Mercury Film Electrode Mercury Plating Solution Move 1. Turn on the instrument and warm it up for 5 minutes For more product details, please visit Aladdin Scientific website.
2. Take 20 mL of the mercury plating solution into a 50 mL beaker. Wash the platinum electrode. Wash and connect the electrode to the instrument, and insert the electrode into the mercury plating solution.
3. Pre-mercury film conditions: electrolysis potential -1 V; recording upper limit -0.9 V; recording lower limit -0.2 V (all relative to SCE), stirring electrolysis 40 s, sensitivity 20, stop 30 s after dissolution, repeated plating and dissolution of mercury 4 times.
4. After the mercury film is plated, remove the electrode from the solution, wash it, and absorb the solution with filter paper. Take 20 mL of water sample, add 2 drops of 1:1 HNO3 in a 50 mL beaker, shake well, immerse the electrode in the solution, electrolysis potential -1.0 V, record the upper limit -0.9 V; record the lower limit -0.2 V, stirring time of 120 s, the sensitivity of 10 under the conditions of electrolytic dissolution, record the E-t curve, read the wave height on the E-t curve, repeat 3 times to see whether it is reproducible.
5. Add appropriate amount of Pb2+ standard solution to the above solution, which can increase the wave height by two times. Electrolyze the solution under the same conditions as above, record the E-t curve, read the wave height and repeat 3 times.
6. Add the same amount of Pb2+ standard solution into the above solution and measure the wave height under the same conditions as above. Based on the wave heights measured in the three times, use the extrapolation method to find out the concentration of Pb2+ in the original water samples, and calculate it in μl/L.