ISOLATION OF CHLOROPHYLL AND CAROTENOID PIGMENTS FROM SPINACH:
What would happen to the Rf values of the pigments if you were to increase the relative concentration of acetone in the developing solvent ?
I said the Rf values would be higher because Acetone is more polar than hexane ... so the components would move faster across the TLC plate. We used 70%hexane-30% acetone for preparing our development chamber. ... I would like to know if my answer is right and if not what's the right answer please. Thanks
I'm pretty sure pigments travel further when they are less polar. Since acetone is more polar then the rf values would be less.
I'm no TLC man but my thinking is the same as yours.
Thanks
Your answer is partially correct. Let me explain it in more detail.
In thin layer chromatography (TLC), Rf value is a measure of how far a particular pigment travels on a TLC plate relative to the solvent front. Rf value is calculated by dividing the distance traveled by the pigment by the distance traveled by the solvent front.
When you increase the relative concentration of acetone in the developing solvent, the polarity of the solvent increases. Acetone is more polar than hexane, so the overall polarity of the solvent mixture increases with an increase in acetone concentration.
In general, polar compounds have a stronger affinity for the stationary phase (usually a silica gel plate in TLC) and tend to move slower on the plate. On the other hand, non-polar compounds have a weaker affinity for the stationary phase and tend to move faster.
Since acetone is more polar than hexane, an increase in the acetone concentration will make the developing solvent overall more polar. This change in polarity will affect the movement of the pigments on the TLC plate.
Chlorophyll pigments are generally more polar than carotenoid pigments. Therefore, an increase in the acetone concentration will result in a larger change in the Rf values of chlorophyll pigments compared to carotenoid pigments. With a more polar solvent, chlorophyll pigments would typically have lower Rf values and move slower on the TLC plate, while carotenoid pigments may have slightly higher Rf values and move faster.
So, to summarize, your answer is partially correct. Increasing the relative concentration of acetone in the developing solvent would generally result in lower Rf values for chlorophyll pigments and slightly higher Rf values for carotenoid pigments.
However, it's important to note that the specific impact on Rf values may vary depending on the exact composition of the pigments and the concentration of acetone. It is always a good practice to perform control experiments and compare the results to understand the effect of changes in the developing solvent on the Rf values.