With acid-base titrations the response time of an electrode determines how quickly it reacts to a pH change of the sample solution and again reaches a stable reading
The Solvotrode combined glass electrode has been developed for non-aqueous acid-base titrations and can be used for applications ranging from acid value titrations in the biodiesel industry, TAN/TBN determinations in the petrochemical industry to perchloric acid titrations in the pharmaceutical industries.
Correct storage and conditioning of the Solvotrode are essential to maintain the performance of this high specification electrode.
The demands placed on a combined pH glass electrode (eg Solvotrode) depend on the particular application.
Various properties such as response time, thermal resistance, chemical stability, shape, size and electrical properties of the electrode have to be taken into account.
The response of a pH electrode is primarily dependent on unhindered contact between the reference electrolyte and the sample solution.
However, it is also influenced by the composition of the pH-sensitive glass membrane of the measuring electrode and by the storage conditions.
The longer the electrode is stored in an aqueous solution, the thicker the solvated layer at the outside of the membrane becomes.
Protons and - to a lesser extent - alkali ions (eg sodium and potassium ions that account for the alkali error at pH values above 11...12) penetrate into the solvated layer.
The thicker this layer, the longer the adjustment time and the poorer the response of the glass membrane.
Long adjustment times also result from excessive dehydration of the solvated layer, for example, when the electrode dries out as a result of incorrect storage or during titration in anhydrous solvents.
In order to obtain reliable results at any time, the response of pH electrodes must be regularly checked.
The amount of cleaning and maintenance work can be considerably reduced by choosing the correct pH electrode and thus the optimal type of diaphragm.
Measuring problems are primarily caused by contamination of the reference electrode diaphragm.
Therefore, maintenance of pH electrodes concentrates on the diaphragm with the pH membrane being of secondary importance.
When in doubt, the reference electrode should be cleaned/regenerated first and the very sensitive measuring electrode second.
Solvotrode for non-aqueous media.
The Solvotrode is the optimal choice for acid-base titrations in non-aqueous media such as oils, dimethylformamide, ethanol, glacial acetic acid and isopropanol.
For example, it can be used in the pharmaceutical industry for the titration of amino acids or amino hydrochlorides in non-aqueous media, in the petrochemical industry for determining the acid or base number in crude oil products or in the food industry for determining saponification or hydroxyl numbers.
It has a robust ground-joint diaphragm made of PCTFE (polychlorotrifluoroethylene) that guarantees a constant flow of electrolyte (usually 2mol/L LiCl in ethanol) and can be easily cleaned.
Together with the electrical shielding of the measuring electrode this largely prevents interference from electrostatic charges and results in low noise titration curves.
In poorly-conducting organic solvents the Solvotrode has a rapid response and provides stable readings.
If you observe a few basic rules before, during and after a titration, your Solvotrode will have a long working life, will not require complicated regeneration procedures and always provide precise results.
These rules are based on the physicochemical properties of the Solvotrode and the above-mentioned requirements for error-free measurements.
Preparing the Solvotrode for a titration:.
Immerse the pH-sensitive glass membrane (but not the ground-joint diaphragm) in distilled water for one minute to hydrate it.
Then, open the filling opening for the reference electrolyte.
Slightly lift the ring-shaped sleeve of the ground-joint diaphragm and allow a little electrolyte to flow out.
Carefully slide the sleeve back into its original position without exerting too much pressure.
Rinse the Solvotrode with distilled water without letting any water enter it's interior.
Fill up the reference electrode to the correct level with electrolyte.
Immediately before the titration rinse the Solvotrode with the solvent used to dissolve the substance to be titrated.
Between titrations:.
Rinse the Solvotrode with the solvent used to dissolve the substance to be titrated.
Rinse the Solvotrode with distilled water.
Check whether the ground-joint diaphragm is blocked, i.e.
whether you can see any deposits in the ground joint.
Rinse the Solvotrode again with the solvent used to dissolve the substance to be titrated.
The solvated layer of the pH-sensitive membrane must be intact.
Non-aqueous solvents dehydrate the glass membrane and as a result increasingly longer response times and flatter titration curves are obtained, i.e.
the pH jumps become less pronounced.
The precision and reproducibility of the results also decrease.
If necessary, the steps mentioned above for preparing the Solvotrode for the titration can be repeated at any time between titrations.
Cleaning after the end of the titration:.
Loosen the ring-shaped sleeve of the ground-joint diaphragm of the Solvotrode.
Remove any contamination of the Solvotrode caused by the sample with a suitable solvent.
Rinse the Solvotrode with distilled water.
Fill up the reference electrode to the correct level with electrolyte.
Titrations in completely anhydrous solvents as well as long storage times can cause the ground-joint sleeve to seize up.
In this case you should immerse the ground-joint diaphragm in hot water for about one minute before you again very carefully try to loosen the sleeve.
Storing the Solvotrode Storage periods of several days: Close the electrolyte filling opening.
Store the electrode in the corresponding reference electrolyte.
Shorter storage periods: Close the electrolyte filling opening.
Immerse the pH-sensitive glass membrane (but not the ground joint diaphragm) in distilled water.
The Solvotrode is the optimal choice for acid-base titrations in non-aqueous media and if you observe a few basic rules before, during and after a titration, your Solvotrode will have a very effective long working life.
