As synthetic chemistry has evolved, so has flash chromatography. Target molecule synthesis is becoming more complicated and the synthetic products more polar. This shift in compound polarity has changed purification strategy from almost entirely normal-phase flash chromatography using silica to a significant percentage of flash chromatography now being reversed-phase during the past 9 or so years.
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.
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.
The newly released Biotage® Selekt flash chromatography instrument can be run at a maximum flow-rate of 300 mL/min or a maximum pressure of 30 bar. These high flowrates and pressures enable a user to perform chromatography using not only dry-packed, single-use plastic flash columns containing small (≥20 μm) spherical silica particles, but also semi-preparative, slurry-packed
HPLC columns for multiple use with smaller (≤20 μm) spherical silica particles.
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.
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.
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:
Method transfer from reversed-phase TLC (thin layer chromatography) to reversed-phase flash column chromatography can be very challenging. Because of this, I often recommend using HPLC for reversed-phase flash chromatography method development. This really is a straight-forward process if you start with the right HPLC column and know a little about your HPLC system's detector.
In this post, I will share some tips on how to develop a reversed-phase flash purification method using HPLC.
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.