Chromotropic acid, a fluorogenic chelating agent for aluminium(III).

Area of Science:

• Analytical Chemistry
• Spectroscopy

Background:

• Aluminium(III) complexation with chromotropic acid is a known reaction.
• Enhancing fluorescence intensity offers a potential analytical tool for aluminium detection.

Purpose of the Study:

• To revisit the complexation of aluminium(III) with chromotropic acid.
• To utilize the fluorescence enhancement for analytical determination of aluminium.
• To investigate and optimize conditions for selective and sensitive aluminium measurement.

Main Methods:

• Complexation of aluminium(III) with chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulfonic acid).
• Investigation of fluorescence enhancement at varying pH and excitation wavelengths.
• Determination of stability constants and interfering species.
• Development of a calibration plot and calculation of detection limits.
• Application to real-world samples (tap water) and comparison with Atomic Absorption Spectroscopy (AAS).

Main Results:

• A 1:1 complex formed at pH ~4 with a stability constant log beta110 = 18.4 ± 0.7.
• Selective excitation of the aluminium chelate achieved at wavelengths > 360 nm.
• Gallium(III) identified as the primary interfering ion; citric acid as the strongest competing ligand.
• A 10⁻² mol L⁻¹ formic acid buffer demonstrated suitability.
• Linear response up to 500 µg L⁻¹ Al(III) with a detection limit of 0.65 µg L⁻¹.
• Successful application to tap water samples, showing good agreement with AAS results.

Conclusions:

• The fluorescence enhancement method provides a sensitive and selective analytical tool for aluminium determination.
• Optimized conditions and buffer systems minimize interference and enhance accuracy.
• The developed method is reliable for analyzing aluminium in environmental samples like tap water.