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.
I have recently posted on how solvent choice influences the separation of hard to resolve compounds using normal-phase flash chromatography. As a chemist with an inquiring mind, I thought I would expand my research beyond normal-phase and see what happens in reversed-phase.
In this post, I share my results.
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.
Acetone, as you know, is a terrific solvent. It dissolves many organic molecules, evaporates easily, is both water and organic soluble, and is cheap (relatively). These attributes tell me it should be a good polar modifier for normal-phase flash chromatography.
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?
In this post I will discuss using normal-phase flash chromatography with aqueous solvents, a form of HILIC (hydrophilic interaction liquid chromatography), to purify those compounds that just will not stick well enough on reversed-phase media.
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.
For most synthesis and natural product chemists, flash chromatography is the primary tool for purification and isolation of compounds of interest. Purification methods include flash system defaulted linear gradients (e.g. 0-100%), active gradient modification (on-the-fly) during purification, and unique method creation based one either the chemist’s experience or TLC data (typically a linear gradient). Rarely do chemists work to optimize the purification to maximize target compound purity by employing a step gradient. In this post, I discuss the value optimized step gradients provide chemists.