Effecten van EDTA op eindpuntdetectiemethoden

End-point detection in EDTA titration includes visual and instrumental methods.

A visual metal-ion indicator, which forms a stable complex with a metal ion to signal the end point by a color change, is also called a metallochromic indicator.

Metallochromic indicators are usually organic dyes and are useful if the indicator forms an intensely colored complex with the metal ion in a different color from the free indicator.

This metal–indicator complex must be weaker than the metal–EDTA complex, but the reversible shift of the reaction must be rapid to see an abrupt color change.

Since metallochromic indicators are usually acid–base indicators, the free indicator color changes with the pH of the solution. So, titration with a metallochromic indicator requires suitable pH ranges.

If the color change at the end point is difficult to detect visually, spectrophotometric methods can monitor the absorbance to identify the equivalence point.

Alternatively, with some metal ions indicator electrodes can be used to measure the change in potential signaling the end point.