Effect of (De-)protonation on the UV Spectra of Sodium Oleate: Experimental and Electronic Structure Investigation
Bibliographic record
Abstract
Sodium oleate (NaOL), an anionic surfactant used in mineral processing, is challenging to quantify in aqueous solutions using UV spectroscopy. This study examined ultraviolet spectral shifts of sodium oleate with and without common pH regulators. Experimental results were supported by quantum chemical calculations at the CAM-B3LYP//6–31++G(d,p) level of theory. Two main absorbance peaks appeared in sequence, at 190 and 232 nm, corresponding to the π → π* and the n → π* electronic transitions of the C═C double bond and COO – functional group, respectively. Under the typical concentration range used in adsorption and flotation studies, the first peak redshifted to reach λ max = 203 nm at 2 mM NaOL, while both solution deprotonation and protonation resulted in hypo/hyperchromicity. By influencing the electronic environment, acidic and alkaline treatments triggered a broadening and narrowing of the NaOL UV spectra. This difference in behavior was associated with the dissociative equilibrium of oleic acid, where protonation was favorable to molecular species, whereas deprotonation favored the ionic oleate species. The HOMO-LUMO excitation energies were higher in the protonated than in the deprotonated environment, explaining the broader spectra obtained experimentally in the former and higher reactivity in the latter. The peak disruptions give rise to significant discrepancies during quantitative measurements of NaOL in aqueous solutions, which may be managed by appropriate precautions and corrective techniques. These findings can be extended to systems similar to the oleate system and may guide experimental and data-processing procedures in UV spectrometry.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".