Retention Characteristics of a pH Tunable Water Stationary Phase in Supercritical Fluid Chromatography
Bibliographic record
Abstract
The retention characteristics of a novel pH tunable water stationary phase are presented. The method utilizes a change in mobile phase from N2 to CO2 to acidify the water phase in situ and control the ionization and elution of organic acids. With N2 present the phase pH > 5.4 and the acids are ionized and strongly retained. Conversely, with CO2 present the pH < 3.8 and the acids are neutralized and can elute. This effect is reasonably independent of time. For example, at 80°C hexanoic acid readily elutes from a 10 m column after switching to CO2 at any point over a 1 h period. Beyond this, however, some broadening and peak erosion is noted. Acids are also retained on 10 and 2 m columns similarly, since their elution primarily depends upon the change in stationary phase pH. Altering the CO2 solubility in the water phase alone (i.e., through changing system temperature and pressure without using N2) also produces similar changes in stationary phase acidity. However, this approach yields greater system noise and instability. The N2/CO2 switching mode is used to analyze organic acids in various samples and is found to provide high selectivity for them over other matrix components. Therefore, this approach can potentially simplify the analysis of such acids in complex samples.
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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 | 0.001 | 0.001 |
| 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 | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".