Potentiometric titration

Measurements, first and second derivative in a potentiometric titration.

Potentiometric titration is a technique similar to direct titration of a redox reaction. No indicator is used, instead the potential across the analyte, typically an electrolyte solution is measured. To do this, two electrodes are used, an indicator electrode and a reference electrode. The indicator electrode forms an electrochemical half cell with the interested ions in the test solution. The reference electrode forms the other half cell, holding a consistent electrical potential. The overall electric potential is calculated as E_cell = E_ind - E_ref + E_sol. E_sol is the potential drop over the test solution between the two electrodes. E_cell is recorded at intervals as the titrant is added. A graph of potential against volume added can be drawn and the end point of the reaction is half way between the jump in voltage.

E_cell depends on the concentration of the interested ions with which the indicator electrode is in contact. For example, the electrode reaction may be

Mⁿ⁺+ne^------>M

As the concentration of Mⁿ⁺ changes,the E_cell changes correspondingly. Thus the potentiometric titration involve measurement of E_cell with the addition of titrant. types of potentiometric titration: acid-base titration (total alkalinity and total acidity), redox titration (HI/HY and cerate), precipitation titration (halides), and complexometric titration (free EDTA and Antical #5).