&lt;p style="margin: 0px; text-align: justify; text-indent: 0.5in; text-justify: inter-ideograph;"&gt;&lt;font color="#000000" face="Times New Roman" size="3"&gt;Understanding the chemistry of metal-loaded ligand species used in extraction of lanthanides and actinides from used nuclear fuel requires that the complexation kinetics of the ligand with the metal be quantitatively established. To date, studies measuring the complexation kinetics of the aminopolycarboxylic acid DTPA (diethylenetriaminepentaacetic acid) with lanthanides (and actinides) have used a dye probe molecule, which creates a colored complex when combined with the metal ion. The probe dye is displaced during the reaction with the complexing agent with the change in UV-visible absorbance measured in a stopped-flow instrument. For this approach to give accurate information about the kinetics of the complexing agent it is essential that the dye has a negligible influence on the reaction to be investigated, i.e. that the probe is weakly bound and can be quickly removed from the metal ion. However, in our investigations the results show that the influence of the dye is significant, and distorts the DTPA complexation. This is demonstrated by the differences in complexation rate constants measured while using a more weakly bound dye such as xylenol orange in contrast to the more strongly bound arsenazo III dye. Xylenol orange gives much faster kinetics for europium complexation with DTPA than arsenazo III. Stronger bound dyes are seen to give even slower kinetics. &lt;/font&gt;&lt;span style="margin:0px"&gt;&lt;font color="#000000" face="Times New Roman" size="3"&gt;Under the assumption of no dye-metal interaction (a perfect probe) the system should be easily interpreted using pseudo-first order kinetics when DTPA is in excess. However, to achieve a reasonable fit on these dye-based experimental data we require a dual exponential model, further indicating that the lanthanide ion interacts significantly with the dye. Consequently, in this study we have re-examined the complexation kinetics for lanthanides under a variety of conditions to elucidate the true, absolute, complexation and decomplexation kinetics.&lt;/font&gt;&lt;/span&gt;&lt;span style="font-size:4pt; margin:0px"&gt;&lt;font color="#000000" face="Times New Roman"&gt; &lt;/font&gt;&lt;span style="margin:0px"&gt;&lt;font color="#000000" face="Times New Roman"&gt; &lt;/font&gt;&lt;/span&gt;&lt;/span&gt;&lt;/p&gt;

Determining DTPA complexation kinetics

253rd National Meeting (2017)

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