Mobile phase was water and ethanol( not a mixture separetely there were 2 TLC pa
ID: 1051321 • Letter: M
Question
Mobile phase was water and ethanol( not a mixture separetely there were 2 TLC paper and 2 eluents) Substances which were spotted were Rhodamine B and Amaranth O. You can see these strucrure at the photo.I did not understand that, water is a polar substances Rhodamine B is also polar. But rhodamine B did not move on the TLC paper. Why?
Also I did not understand that amaranth O and water went together. On the TLC paper, solvent(water) level was the same with Amaranth O. Amaranth O spot was on the solvent level and Rf value of it was approximately 1. Howevet although Rhodomine B is also polar, it did not move with polar molecule,water. Why? Dyes O Nat HO O- COOH Amaranth[5] Rhodamine B [4] B41
Explanation / Answer
Rhodamine B is polar, amino acid type molecule, having amino group and acid group. In TLC the silica gel acts as the stationary phase and the solvent acts as the mobile phase. this bind with silica more and water solubulity is less. Aamaranth O this contain sulfoniac acid salt group and more soluble in water compare to rhodamine B. Rhodamine dyes fluoresce and can thus be detected easily and inexpensively with instruments called fluorometers. When comparing two different compounds run under identical chromatography conditions (same mobile phase) the larger the distance compound travels on the TLC plate, the compound with the larger Rf is less polar because it interacts less strongly with the polar adsorbent on the TLC plate. the smallar distaance traves it strongly bind with silica , this is more polar.