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Well, acutally what you said is indeed always the case, because practically TLC plate is mainly used to separate organic compounds whose polarities are usually not as high. We seldom use high-polar solvent like methanol alone for compound separation. But what I said is based on a wider perspect. It\’s like a universal law. In pratical use, we find the best solvent mixture through continuous adjustment of the ratio of polar and non-polar solvents.
