Preconcentration of Trivalent Lanthanide Elements on a Mercury Film from Aqueous Solution Using Rotating Disk Electrode Voltammetry

Preconcentration mechanism of trivalent lanthanum on eQCM electrodes in the presence of α-hydroxy isobutyric acid

Electroprecipitation can be used to preconcentrate lanthanum on carbon electrode surfaces. The use of complexing ligands is expected to improve the electroprecipitation of lanthanum by protecting La ions in solution from the alkaline region near the electrode surface. However, the electroprecipitation mechanism of La in the presence of a complexing ligand is not known. The goal of this work is to 1) determine the effect of the complexing ligand, α-hydroxy isobutyric acid (HIBA), on the electroprecipitation of La onto the gold electrodes, and 2) identify the changes in the mechanism of accumulation when preconcentrating in the presence of HIBA. We used an electrochemical quartz crystal microbalance (eQCM) and needle type pH microelectrodes to determine pH near the electrode surface in combination with cyclic voltammetry to understand the electroprecipitation mechanism. We used the bi-dentate ligand HIBA as a ligand and found that lanthanum electroprecipitation is hindered in the presence of HIBA. The presence of HIBA also delayed the onset of film formation during a cyclic voltammetric experiment by ~100 mV compared to experiments performed without HIBA. The shift in onset potential is attributed to the buffering action of HIBA (pK_a = 3.7) since the shift is not present in subsequent scans. The precipitated film was characterized by scanning electron microscopy, X-ray photoelectron spectrometry, and Auger nanoprobe spectrometry. While we found that La(OH)₃ was the predominant chemical state of the film on electrodes in the absence of HIBA, La₂O₃ was found for films created in the presence of HIBA. Our finding demonstrates that La(OH)₃ can be electrodeposited at room temperature.

Optimization of the electrochemical pre-concentration of trivalent lanthanum from aqueous media

Electrochemical pre-concentration has been shown to effectively increase sample sensitivity and decrease processing time; however, the basic mechanism and optimal conditions of the technique remain unknown, specifically for lanthanides. To gain a better understanding of the mechanism of action, the aqueous solution conditions required to maximize the electrochemical pre-concentration of lanthanum (La) were studied. Parameters investigated included pH, applied potential, and ionic strength. To further optimize and elucidate the mechanism of lanthanide pre-concentration, specific interactions of lanthanum with the mercury film electrode were studied. Three possible mechanisms were proposed based on preliminary observations, including ligand bridging, hydroxide formation, and amalgamation.

Central composite design optimization of Ce(iii) ion removal from aqueous solution using modified SBA-15 mesoporous silica

HESI-SBA-15 was used as an effective adsorbent for cerium ion removal in real samples.

Extraction of lanthanides using 1-hydroxy-6-N-octylcarboxamido-2(1H)-pyridinone as an extractant via competitive ligand complexations between aqueous and organic phases

Increased lanthanide extraction by octyl-HOPO improves the TALSPEAK process and allowed for a greater separation of lanthanides from actinides.

Cathodic preconcentration of f-elements on a mercury film carbon fiber disk microelectrode

Field detection and quantification of f-elements is an important problem in radioanalytical chemistry requiring small, portable devices. Here, characterization of a 10 μm Hg film carbon fiber disk microelectrode to accumulate f-elements is described. Accumulation was performed by cathodic deposition and evaluated by anodic stripping and subsequent ICPMS analyses. La(3+) was used as the model element, and subsequent studies were conducted on a 17 element mixture (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Th). In the model studies, La(3+) undergoes a sorption phenomenon, and as in other studies and confirmed by ICPMS, a monolayer of atoms on the electrode surface is formed. Dissolved O(2) was found to have no effect on the cathodic accumulation of La(3+). Consideration of electrode reaction conditions is made, and reactions are hypothesized. The limit of detection (LOD) was found to be 10(-7) M with mass detection of 10(9) atoms, approximately 5 orders of magnitude less than at conventionally sized electrodes. To solve a dilution problem in follow-on analyses, a suggestion to use microelectrode chip-based sensors was made.