Selectivity enhancement of Arsenazo(III) reagent towards heavier lanthanides using polyaminocarboxylic acids: A spectrophotometric study

• L1/L2/L3/L4 and Arsenazo III with Ce(III)/Nd(III) exhibits 3 absorption bands: 538 nm, 610 nm and 654 nm.
• L1/L2/L3/L4 and Arsenazo III with Dy(III)/Tm(III)/Lu(III) exhibit only one absorption band at 538 nm.
• Nd(III) and heavy lanthanides can be successfully determined with using L1 and L2.
• Effect of EGTA and HEDTA on Arsenzo(III)–Ln(III) complex is very weak.

A new study has been conducted to quantify lanthanide(III) ions using Arsenazo III–polyaminocarboxylic acid (PACA) system. The study disclosed two different analytically important information: (i) λmax of lanthanide–Arsenazo III complexes for lighter lanthanides like Ce(III) and Nd(III) did not shift from its original position on addition of PACA and (ii) for heavier lanthanides like Dy(III), Tm(III) and Lu(III) a new λmax at 538 nm was observed, while wavelengths at 610 nm and 654 nm were disappeared in presence of ethylenediaminetertracetic acid (EDTA) and trans-1,2-Diaminocyclohexane-N,N,N′,N′-tetraacetic acid (DCTA), further the intensity of peak decreased with increase in lanthanide(III) ion concentration. Effect of ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA) and N-(2-hydroxyethyl) ethylenediamine-N,N′,N′-triacetic acid (EDTA-OH) on Arsenzo(III)–Ln(III) complex is very weak and there is no analytically importance of such interaction. Moreover, this work confirms that Nd(III) and heavy lanthanides can be successfully determined with high accuracy in the working range of concentration of these metal ions.

The study reveal two different analytical important behaviours: (i) absorbance of lanthanide–ArsenazoIII complexes for lighter lanthanides like Ce(III) and Nd(III) did not shift λmax from its original position in presence of polyaminocarboxylic acids. (ii) For heavier lanthanides like Dy(III), Tm(III) and Lu(III) a new wavelength maximum at 538 nm was observed, while wavelengths at 610 nm and 654 nm disappeared in presence of ethylenediaminetertracetic acid (EDTA) and trans-1,2-Diaminocyclohexane-N,N,N′,N′-tetraacetic acid (DCTA), further the intensity of peak decreased with increase in lanthanide(III) ion concentration.Figure optionsDownload as PowerPoint slide