We did TLC and column chromatography separating methylene blue and fluorescein.

Question

We did TLC and column chromatography separating methylene blue and fluorescein. The solvent contained mostly ethanol but also had NaOH, and this NaOH formed SiO- with the silica (the stationary phase), which is in competition with the solvent for interaction with analyte.

Could someone explain this competition and interaction? I know that chromatography is based on the attraction with the stationary phase or mobile phase. In this experiemnt, the more polar it is, the less Rf value is. I'm just not sure what NaOH does here and how the SiO- ion would interact with the analyte.

Explanation / Answer

Not all analytes re non-polar hydrophobic substance, but even those are detected by allowing them to be bound to beads with which they show affinity. The different weights added by the beads allows to monitor their elution fairly one-at-a-time, necessary for a non-chaotic non-contaminated chromatogram. Substances that are amphoteric like proteins, with one ionizable motif, one polar motif, and one hydrophobic motif are detected by their anion and cation exchange pattern, and so are large molecules that are polar and or ionizable. The different affinity to one ion or the next and their tendency to exchange cations or anions is part of the information. If some of those substances are biologically, they can adopt several conformations. The one they adopt in living systems i usually the active one, and in that conformation they interact in nature with the ions and hydrophylic proteins of our bodies' liquid compartments. Also information is derived from their affinity to the other substances, the beads, the eluents, and the ions, and the overall pH.

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.