# Complexation of Plutonium and Other Actinides in Different Oxidation States with Gluconate at Low pH ValuesA CE-ICP-MS Study

## TL;DR

This study uses CE-ICP-MS to investigate how plutonium and other actinides form complexes with gluconate at low pH, comparing their behavior to redox analogues.

## Contribution

The paper introduces a CE-ICP-MS method to determine complexation constants for plutonium and other actinides in different oxidation states with gluconate.

## Key findings

- Plutonium in oxidation states III, V, and VI behaves similarly to redox analogues in forming gluconate complexes.
- Complex formation constants for Am(III)/Pu(III) and Np(V)/Pu(V) were determined, showing agreement with previous literature.
- Th(IV) forms more binary complexes with gluconate compared to Pu(IV), which forms mixed Pu–OH–GLU complexes.

## Abstract

Using a coupling between capillary electrophoresis and
ICP-MS (CE-ICP-MS),
the gluconate (GLU) complexation of plutonium in the major oxidation
states (III)–(VI) as well as Am­(III), Th­(IV), Np­(V), and U­(VI)
was investigated at pH ≤ 4. CE-ICP-MS enabled the determination
of the Pu oxidation state by comparing its electrophoretic mobility
to that of a redox-analogous actinide (An). For the Am­(III)/Pu­(III)
pair, the complex formation constants of three successive binary [An­(GLU)
x
]3–x
(x = 1–3) complexes could be determined. For Np­(V)/Pu­(V),
the complex formation constants of the first binary [AnO2(GLU)](aq) complex were determined in accordance with
previous literature for Np­(V), and those of the second [AnO2(GLU)2]− complex were estimated. For
U­(VI)/Pu­(VI), the constants of the [AnO2(GLU)]+, [AnO2(GLU–H)](aq), and
[AnO2(GLU–H)­(GLU)]− complexes were also determined in accordance with previous literature
for U­(VI). Plutonium in the oxidation states (III), (V), and (VI)
behaved very similarly to the redox analogues. This was not the case
for Th­(IV)/Pu­(IV). Here, the first five binary [Th­(GLU)
x
]4–x
(x = 1–5) complexes were determined for Th­(IV), whereas
mixed Pu–OH–GLU complexes were proposed for Pu­(IV).
The comparison of the first complex formation constants of the binary
An–GLU complexes suggests a different bonding motif between
An3+/4+ and AnO2
+/2+, with AnO2
+/2+ forming the weaker complexes.