Which chromogen will not produce a colored complex with iron for spectrophotometric measurement?

• A. Bathophenanthroline
• B. B-Hydroxyquinoline
• C. Tripyridyltriazine
• D. Ferrozine

Answer: (B)

In spectrophotometric measurement of iron, you rely on a chromogen that forms a strongly colored and stable complex with iron under the assay conditions. This colored complex provides the signal you quantify with a visible light spectrophotometer, so the key requirement is a reagent that produces a vivid color when bound to iron, allowing sensitive and reliable detection.

Bathophenanthroline, ferrozine, and tripyridyltriazine are classic chromogens for iron because they form intense, well-defined colored complexes with iron ions (Fe2+ or Fe3+ after reduction), yielding clear absorbance peaks in the visible spectrum. This makes them highly suitable for accurate measurement.

B-Hydroxyquinoline, on the other hand, can chelate iron but does not produce a strongly colored complex in the visible range under typical assay conditions. Its iron complex tends to have weak absorption or falls outside the convenient detection wavelengths, limiting sensitivity and reliability for routine spectrophotometric iron assays. Hence, it is not used as the chromogen for this purpose.