The IONODE make Ionode solid-state Surfactant Electrode indicates the potentiometric endpoint when titrating anionic or cationic surfactants in solution. The specially designed solid-state surfactant electrodes will allow the end user to re-generate the active surface.
Anionic surfactants can be titrated with cationic surfactants and vice versa. In contrast to the classical “two-phase titration” according to Epton, the titration with the anionic and cationic surfactants electrodes can be performed without chloroform.
The surfactant ISE provides help here in many cases and also benefits the environment. It has been specially developed for surfactant determinations using potentiometric indication.
Prior to first usage, or after long term storage, just remove the protection cap from the bottom of the electrode and immerse the electrode in deionized water for thirty minutes.
Remove rubber sleeve placed over the filling hole.
The reference half-cell of the combination electrode (or the reference chamber of the reference electrode) should be filled with 3M KCL filling solution
Connect the electrode to the meter.
CLEANING, RECONDITIONING, AND STORAGE
Acidic (or alkaline) rinse solution should be used to rinse the electrode between measurements.
To recondition an electrode when the response had become noisy, sluggish, or irreproducible, soak in slightly acidic (or alkaline) deionized water for about one hour to clean the membrane.
Surfactant Electrode may be stored in deionized water for short periods of time. For storage over 3 weeks, rinse and dry the membrane element and cover the tip with any protective cap shipped with the electrode(s).
The reference half-cell of the combination electrode (or the reference chamber of the reference electrode) should be drained of filling solution, and the rubber sleeve placed over the filling hole.
The electrode is best conditioned by two to three titrations whose results should be ignored.
Adherent deposits are removed with a lint-free tissue paper, moistened in methanol. In sample changer operation, the electrodes are dipped briefly in methanol, while stirring.
The electrode (PVC membrane) is not resistant towards almost any organic solvents. Chloroform, hydrocarbons, acetone, MIBK, tetrahydrofuran, etc. destroys the electrode. High proportions of methanol (30 – 40%) or ethanol (20%) in the solvent shorten the lifetime of the electrode.
Several thousand titrations can be performed with the electrode under normal conditions. Evidence of a decrease in the responding behaviour of the electrode is shown in flatter titration curves and a shortened potential range. For a short time, such an electrode can be regenerated by submerging it for 30 min. in a sodium dodecyl sulphate solution (0.005 mol/L). If this does not help, the electrode must be re-generated (refer to re-generation section) or replaced.
The surfactant electrode will last six months in normal laboratory use. Continuous titrations on an automatic sample changer might shorten operational lifetime to several months. In time, the response time will increase and the titration endpoint breaks will not be as sharp. At this point, titration is impossible and electrode replacement is required.
ELECTRODE SURFACE RE-GENERATION
To regeneration of the sensitive surface, the regeneration kit is required. Remove the spent membrane by rubbing against P4000 polishing paper supplied until the silverish coloured substrate is fully exposed. Then using a cotton tip soaked with 1 µm micro-polishing agent to rubbing against the surface for around 1 minute. Rinse off with deionised water, wait the surface dry before application of the regeneration solution.
Put the electrode upside down with the polished surface facing up. Pipette 100 µL of the regeneration solution from the vial and drop it onto the silverish surface. Make sure it covers all the metal surface. And let it dry naturally. The electrode will be ready to use the next day.
- Response time
The time for the analysis may vary, depending on the sample, the titrant, the method, and the equipment used. The average time for manual titration of anionic surfactants is 2-5 minutes.
The surfactant electrode should be used in the operating range of 0-40°C. The membrane may be permanently destroyed at other temperatures.
The reproducibility of the surfactant electrode can vary significantly on the good laboratory practices of the technician, but will usually be less than 1% with manual techniques and less than 0.5% with automatic techniques.
- Detection limit
For anionic surfactants, the lower limit of detection is 10 ppm. Good laboratory practice and selection of titrant may allow lower levels of detection for some sample types.
- pH Effects
The surfactant electrode has an operating pH range of 2 – 12. Use at other pH values can adversely affect the membrane.
For anionic, sulphated and sulphonated surfactants, the analysis should take place at a pH between 2.5 and 4.5. For other samples, the pH range may need to be adjusted. Polyacrylates require adjustment to pH 10, for example.
Interferences may be caused by any organic anion or cation which chemically resembles the species of interest.
Minimum level of SLS which can be titrated: 10-5M
Maximum level of SLS which can be titrated with 0.05M Hyamine: 5 x 10-2M
pH Range: 2 – 12
Temperature Range: 0 – 40°C
Resistance: 100 Ohms
Size: 120 mm length
12 mm diameter
Storage: store in deionised water (short term) or store dry