In previous posts I have touched upon various sample loading options and how they impact flash chromatographic performance, primarily in normal-phase flash purification. As the use of reversed-phase flash chromatography has steadily increased over the past few years I thought it would be a good idea to discuss one of the most important factors impacting its success.

In this post I discuss the results of some of my original research studying the impact of injection solvent choice on reversed-phase flash separations.

TLC is the tool most used for normal-phase flash chromatography method development. For many chemists, a solvent system of hexane (or heptane) + ethyl acetate is the first, and sometimes only, solvent system evaluated. Though often useful, ethyl acetate may not always provide the optimal purification conditions.

For most organic and medicinal chemists flash chromatography is just another step in the synthesis work flow - react, analyze, purify, react, analyze, purify... until the final product is made. The desired product of each reaction, and the mixture of other species present are, of course, different with each cycle.  Separating the desired compound efficiently without a lot of hassle is something I have written about in this post as well as in others in this series.

In this post, I've written about how that TLC (thin layer chromatography) plate you use for monitoring your reaction can be used to create reliable, efficient, effective gradients.

Purifying polar organic compounds can be very challenging. In a previous post I have discussed using reversed-phase flash chromatography to retain and purify ionizable and ionic compounds.  My colleague, Dr. Elizabeth Denton, has also posted a blog on purifying very polar peptides as well.  Sometimes, however, despite all your efforts with reversed-phase, success is elusive. When this happens, what do you do?

Your choice of sample loading technique can, and likely will, affect the separation and purity of your targeted compound. While liquid loading is easy and often fit for purpose, it can provide some issues especially if large sample volumes are required relative to column size (> 1% of a column volume) or the dissolution solvent is too strong for the chosen purification method (e.g. injecting a methanol-solvated sample into a hexane/ethyl acetate mobile phase).