Related Experiment Video
Updated: Jun 15, 2026
05:52
Measuring the Induced Membrane Voltage with Di-8-ANEPPS
Published on: November 19, 2009
Donnan membrane technique (DMT) for anion measurement.
Flora Alonso Vega1, Liping Weng, Erwin J M Temminghoff
1Department of Soil Quality, Wageningen University, P.O. Box 47, 6700 AA, Wageningen, The Netherlands.
Analytical Chemistry
|March 13, 2010
Summary
The Donnan membrane technique (DMT) accurately determines free anion concentrations. Equilibrium times vary by ion type and ionic strength, with organic acids not crossing the membrane.
Area of Science:
- Environmental Chemistry
- Analytical Chemistry
- Physical Chemistry
Background:
- The Donnan membrane technique (DMT) is a method for determining ion concentrations.
- Understanding free anion concentrations is crucial in various environmental and chemical analyses.
- Previous work focused on cation DMT, necessitating adaptation for anion analysis.
Purpose of the Study:
- To develop and test the Donnan membrane technique for determining free anion concentrations.
- To investigate the influence of ion type and background ionic strength on equilibrium times.
- To explore methods for differentiating anion species of the same element using DMT.
Main Methods:
- Application of the Donnan membrane technique (DMT) with various anions (Cl-, NO3-, SO4(2-), SeO4(2-), H2PO4(-)).
- Monitoring equilibrium times under different ionic strengths (2-200 mM KCl or K2SO4).
- Utilizing a previously developed transport model for cation DMT to analyze anion transport kinetics.
Main Results:
- Equilibrium times ranged from 1 day (Cl-) to 14 days (H2PO4(-)), influenced by ion type and ionic strength.
- Ionic strength had the strongest effect on H2PO4(-) equilibrium time, followed by SO4(2-)/SeO4(2-), then Cl-/NO3(-).
- Negatively charged organic particles (fulvic/humic acids) were retained by the membrane.
- Two novel approaches were tested for measuring different anion species (e.g., SeO4(2-) vs. HSeO3(-)) based on kinetics and ionic strength response.
Conclusions:
- DMT is effective for measuring free anion concentrations, with predictable equilibrium times.
- Transport is diffusion-controlled in solution at low ionic strength and in the membrane at high ionic strength.
- The technique shows promise for distinguishing between different oxidation states or species of the same element.
Related Concept Videos
01:15Dialysis
Dialysis is a diffusion-based purification process that separates analyte molecules from a complex matrix. This is accomplished by allowing molecules in the solution to pass through a semipermeable membrane into a liquid on the other side. The membrane is usually made of cellulose acetate or cellulose nitrate, and the second liquid must be miscible with the solution. Ions (e.g., chloride or sodium) or organic molecules (e.g., glucose) can pass through the membrane pores, which generally have...
01:23EDTA: Indirect and Alkalimetric Titration
Unlike direct titration, back-titration, and displacement titration, indirect titration is an EDTA titration method for quantifying anions. In the indirect titration method, anions are precipitated as their insoluble salts with excess metal ions. The filtrate containing the excess metal ions is directly titrated with standard EDTA until the endpoint is achieved. Another approach involves extracting the metal ion and back-titrating with standard EDTA to obtain the endpoint. In this way, the...