For medicinal chemists, maximizing the synthetic yield of their newly created intermediate compound is their priority. More times than not, flash chromatography is used to purify these intermediate compounds to at least 80% purity. Final compounds, however, not only require high yield but maximum attainable purity, typically in excess of 95%. For this purity level, chemists will either send the reaction mixture to an in-house prep HPLC lab or perform their own preparative HPLC compound purification, if it is available in the lab.
In my previous post, I talked about the "Chemistry Behind Normal-phase Flash Chromatography", the most common form of liquid-solid chromatography. In this post, I focus on reversed-phase flash chromatography and how it differs from normal-phase.
I am often asked why reversed-phase TLC data does not translate well to reversed-phase flash column chromatography. There are several reasons for this and in this post I will attempt to explain the challenges associated with reverse-phase TLC as a method development tool for reversed-phase flash chromatography.
Choosing a good purification strategy is an important for successful crude compound purification. A major factor in your strategy is choosing between normal-phase or reversed-phase chromatography. How do you choose?
In this post, I will provide some simple guidance on helping determine which route to take.
When it comes to the purification of polar, water-soluble compounds reversed-phase chromatography is the most commonly used approach. However, because of strong stationary phase – mobile phase repulsion forces, the use of highly aqueous (90-100% water) solvent systems has been shown to provide less retention than needed. This issue has led to the development of “aqueous compatible” reversed-phase media.
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 how 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.
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.
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.
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.