Selectivity and solvent strength are the most important factors that determine success or failure of a chromatographic separation. These two independent dynamics apply to both normal and reversed-phase chromatography, and should be optimized, especially when high fraction purity is needed.

In this post on the Flash Purification Blog, Bob Bickler discusses the impact of elution solvent choice on both normal and reversed-phase purification. He concludes:

"So, to get the best flash purification results, evaluate various strong solvents and solvent ratios with miscible weak solvents during method development. You may be pleasantly surprised with the results."