Determination of Trace Potassium Permanganate in Tap Water by TMB Method
This protocol is adapted from research data and provided for reference only. Adjustments may be necessary based on specific experimental requirements.
(1) Reagent Preparation: Dissolve TMB in dimethyl sulfoxide (DMSO) to prepare a 0.10mol/L stock solution, which is further diluted to working concentration (e.g., 5mmol/L) before use; Prepare 10mmol/L HCl solution; Prepare a series of KMnO₄ standard working solutions using deionized water.
(2) Solid Phase Extraction Column Preparation: Pack 50mg of 200-400 mesh polyamide 6 (PA-6) powder into a 2mL polypropylene empty column tube (inner diameter 9mm) using the dry method. Fix both ends of the column tube with polyethylene sieve plates to ensure the adsorbent surface is flat and compact. Before use, sequentially wash and activate the column tube with 1mL DMSO and 2mL deionized water.
(3) Sample Pretreatment: Tap water samples need to be vacuum filtered through a 0.15μm polytetrafluoroethylene (PTFE) microporous membrane to remove particulate matter.
(4) Enrichment and Detection of Potassium Permanganate: Take 100mL water sample (pH=6-8) and vacuum filter it through the PA-6 solid phase extraction column at a flow rate of 30mL/min. Permanganate ions (MnO₄⁻) are selectively adsorbed onto the adsorbent through hydrogen bonding. Wash the column tube with 2mL deionized water to remove unadsorbed substances. Add 1mL of mixed solution consisting of 10mmol/L HCl and 5mmol/L TMB working solution to the column. Push the solution into the column using a plunger to contact with the adsorbent, and let it react for 3 minutes. During this process, the adsorbed MnO₄⁻ oxidizes TMB to produce blue oxidation products (ox-TMB), while itself is reduced to Mn²⁺. Push the blue reaction solution out of the column tube and measure its absorbance at 370nm wavelength using a spectrophotometer.
Precautions:
(1) This method shows good linearity in the concentration range of 0.01-1μmol/L, with a detection limit for MnO₄⁻ in deionized water as low as 5.1nmol/L.
(2) The TMB oxidation product maintains good stability within 30 minutes, which is beneficial for detection.
(3) For your safety and health, please wear a lab coat and disposable gloves during operation.
References:
[1] Hao L, Qi Y, Wu Y, et al. Determination of trace potassium permanganate in tap water by solid phase extraction combined with spectrophotometry. Heliyon. 2023 Feb 8;9(3):e13587. |
