One of the more challenging purifications is that of water-soluble, ionizable compounds. Typically, normal-phase with silica is not used because of the probable non-reversible interactions, especially between the ionized amines interacting and the ionizable silanols.  With normal-phase out of the purification solution that leaves ion exchange and reversed-phase as chromatographic options.

In this post I will discuss the use of reversed-phase and the influence pH and buffers have on the chromatography of some ionic, water soluble compounds.

This question is one that is increasing in frequency. Over the past 10 or so years reversed-phase flash chromatography use has increased dramatically. Likewise, reversed-phase preparative HPLC (RP pHPLC) use has also increased. Chemists need to know when to choose between the speed and low solvent use of flash column chromatography and the ultimate purification of RP pHPLC. With this as the backdrop, let me give you my thoughts on hot to choose between flash chromatography and when it is best to use RP pHPLC.

How to choose between normal- and reversed-phase flash column chromatography is an excellent question and one that my readers often ask.  Those who use column chromatography know that as long as the reaction products or compounds are fairly non-polar and near neutral pH they will have successful purifications.  However, when your mixture's chemical characteristics are more challenging (polar, non-polar, basic, acidic) there are other options that are available to successfully separate pure compounds.

In this post, I will discuss the criteria you can use to guide your choice between normal- or reversed-phase flash chromatography.

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.

Tetrahydrocannabinol, aka THC, is a hallucinogen found in cannabis and, to a lesser degree, in hemp.  Though THC is legal in some locations in the US and Canada, there is a growing market for its non-hallucinogenic cousin, cannabidiol (CBD), which has purported medical benefits.

The problem with isolating CBD from cannabis and hemp is contamination from THC, which is typically present at a moderate to high percentage. In this post, I will provide some insight into rapidly purifying CBD to remove THC.

Using a “dry” loading technique with flash chromatography typically improves compound purity and overall separation quality compared to liquid loading. The reasons for this I have prophesized previously and include:

For chemists, flash chromatography is part of their everyday synthesis workflow. For most syntheses, crude reaction mixtures are purified by normal-phase (aka adsorption) chromatography.  There are times, however, where the crude mixture’s complexity and polarity make normal-phase chromatography very challenging.  For these situations, reversed-phase (aka partition) chromatography may be a preferred option.

But, if you have only one flash system available, can you, should you, and how do you efficiently switch from non-polar, normal-phase solvents to polar, reversed-phase solvents – and back again without issues? In this post I'll attempt to shed some light on the topic.

The answer to this question is yes, reversed-phase can sometimes provide a better separation and thus better purification than normal-phase.  When is reversed-phase likely to be the better choice is a different, and likely better, question.

In this post I will try to demonstrate when reversed-phase is likely the better purification mode.

Reversed-phase flash chromatography usage is increasing rapidly. In fact, over the past 10 or so years, reversed-phase flash chromatography use has increased a dramatic 650%! This is amazing growth despite the fact that reversed-phase flash columns are considerably more expensive than silica columns and you need to evaporate water from your fractions. So, what’s driving this change in chemists’ modus operandi?

In this post, I will explain why chemists are increasingly using reversed-phase flash chromatography for routine, intermediate, and final compound purification and provide and example as well.