Electrochemical Determination of Dopamine with a Carbon Paste-Lanthanum (III) Oxide Micro-Composite Electrode: Effect of Cetyl Trimethyl Ammonium Bromide Surfactanton Selectivity.

This paper presents a new application of a lanthanum oxide (III)-modified carbon paste electrode (LaOX/CPE) for dopamine (DP) detection in the presence of ascorbic acid (AA). The presence of cetyl trimethyl ammonium bromide (CTAB) facilitated the LaOX/CPE electrode's ability to detect DP amidst AA interference, resulting in a substantial 70.0% increase in the anodic peak current for DP when compared to the unmodified carbon paste electrode (CPE). CTAB enabled clear separation of the anodic peaks for DP and AA by nearly 0.2 V, despite their initially overlapping potential values, through the ion-dipole interaction of AA and CTAB. The electrode was characterized using cyclic voltammetry (CV) and energy-dispersive spectroscopy (EDS). The method demonstrated a detection limit of 0.06 µmol/L with a relative standard deviation (RSD) of 6.0% (n = 15). Accuracy was assessed through the relative error and recovery percent, using urine samples spiked with known quantities of DP.

Investigative Analysis of Lanthanum Oxide Nanoparticles on Elements in Bone of Wistar Rats After 30 Days of Repeated Oral Administration.

Accumulation of lanthanum oxide nanoparticles (La2O3NPs) in the femur bone of rats after 30 days of oral administration was explored. Also, the influence of La2O3NPs on macro and trace elements in the rats' femur bone was assessed. Inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical spectrometry (ICP OES) were used for total element determination in the bone after decomposition while laser ablation-ICP-MS (LA-ICP-MS) was used to investigate element distribution (bio-imaging) in the bone. Some differences in element concentrations in the bone between the rats treated with La2O3NPs at 1.0 mg kg-1 (T1), 10.0 mg kg-1 (T2), and 100 mg kg-1 (T3) body weight (bw) and the control rats (CTR) were observed. More differences were observed in the bone of rat treated with 10.0 mg kg-1 La2O3NPs bw. However, the highest change observed was for Mg, which concentration ranged from 5230 ± 12 µg kg-1 for the CTR group to 4130 ± 138 µg kg-1 for the T3 group. Minor changes were observed for Ba, Ca, Cr, Cu, Fe, Mg, Na, Pb, Sr, and Zn between CTR and animals treated with La2O3NPs at the different levels of concentration. It was possible to observe from LA-ICP-MS analysis that La2O3NPs were accumulated only on the surface of the bone, not deeper than about 5 µm. LA-ICP-MS allowed also to investigate the distribution of La and the other elements in a cross section of the femur bone head, where higher amounts of the elements are present at the external part of the bone. Therefore, it was demonstrated that La2O3NPs are incorporated on the surface of the bone and it has a small influence on some of the other elements evaluated.

Rare Earth-Based Compounds as Inhibitors of Hot-Corrosion Induced by Vanadium Salts.

In this study, the performance evaluation of lanthanum compounds as corrosion inhibitors of vanadium salts was performed. The inhibitors tested were lanthanum acetate and La2O3. The performance of the inhibitors was tested using sodium metavanadate (NaVO3) as a corrosive medium at 700, 800, and 900 °C. The corrosion inhibitory effect was evaluated on the corrosion process of 304H stainless steel. The corrosion rate of the steel was determined by the mass loss technique after 100 h of immersion in the corrosive salt with and without the addition of the corrosion inhibitor. The results show that lanthanum compounds act as corrosion inhibitors of vanadium salts. The inhibitory effect increases by increasing the concentration and tends to decrease when increasing the test temperature. Lanthanum compounds act as excellent corrosion inhibitors due to their ability to stabilize vanadium cations. Vanadium is stabilized by forming a new compound, lanthanum vanadate (LaVO4), with a melting point much higher than the compounds formed when Mg or Ni compounds are used as corrosion inhibitors.

Fabrication of Sputtered Ce/La, La/Ce Oxide Bilayers on AA6061 and AA7075 Aluminum Alloys for the Development of Corrosion Protective Coatings.

This work provides a comparative study on the corrosion protection efficiency of Ce, La films as well as Ce/La and La/Ce oxide bilayered coatings deposited onto AA7075 and AA6061 substrates by the radio frequency (RF) magnetron sputtering technique. The coating thickness ranged approximately from 12 to 835 nm, which changed with the deposition parameters and substrate composition. The relationship between microstructure, roughness and electrochemical performance is examined. The reactivity and crystallinity of rare earth (RE) films can be tailored by adjusting the sputtering parameters. Sputtered La films with thickness ca. 390 nm and average roughness of 66 nm showed the best corrosion protection properties in chloride medium as determined by potentiodynamic curves and electrochemical impedance spectroscopy (EIS). The method to obtain RE bilayered coatings, i.e., La/Ce or Ce/La as well as the substrate composition and applied power conditioned their inhibition properties. The RE bilayered coatings displayed better barrier properties than Ce films, which were poorer than those featured by La films.