Very polar compound purification using aqueous normal-phase flash column 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. Continue reading Very polar compound purification using aqueous normal-phase flash column chromatography

When should I choose APCI or ESI for my flash column chromatography?

Mass spectrometers today are typically available with either Electrospray Ionization (ESI) or APCI (Atmospheric Pressure Chemical Ionization) sources.  That’s really nice but, how do you know which source will work best when purifying your sample?

In this post I attempt to provide some guidance to selecting the ionization source best suited to your sample types. Continue reading When should I choose APCI or ESI for my flash column chromatography?

5 Tips on extending reversed-phase flash chromatography cartridge life

With reversed-phase flash column chromatography becoming increasingly popular for routine purification, understanding how to make the cartridges last (since they cost more) is important to know. 

In this post I will mention a few tips to prolong reversed-phase cartridge life.

Continue reading 5 Tips on extending reversed-phase flash chromatography cartridge life

Does high performance flash column chromatography require high performance TLC for method development?

Higher performance flash cartridges are becoming all the rage these days.   Chemists are using them for challenging as well as for routine purification.   As a result, I am often asked, “do I need high-performance TLC plates for method development?”

In this post I will explain why the answer is no.

Continue reading Does high performance flash column chromatography require high performance TLC for method development?

How do I decide between normal- or reversed-phase flash column 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.

Continue reading How do I decide between normal- or reversed-phase flash column chromatography?

How does media pore size impact small-molecule flash column chromatography?

For most chemists, flash purification is a means to an end. In other words, it is a tool needed to purify and isolate one compound from a mixture of compounds so that the next reaction can occur with reduced by-product formation. Other than choosing between normal– or reversed-phase, there typically is not much thought put into cartridge selection, especially not related to stationary phase media porosity.

For most small molecules, this approach makes sense, but for larger molecules and very lipophilic compounds, factoring for media porosity should be included.  In this post, I will discuss the impact media porosity can have on chromatographic performance.

Continue reading How does media pore size impact small-molecule flash column chromatography?

How to prevent compound precipitation during flash column chromatography

Compounds precipitating during flash chromatography is at best an inconvenience when working up your crude reaction mixture.  Precipitation during purification typically happens in the column or in the tubing exiting the cartridge.

In this post, I will propose a strategy that can minimize and perhaps prevent this issue from occurring.

Continue reading How to prevent compound precipitation during flash column chromatography

When should I use a pH modifier in flash column chromatography gradient?

Have you ever experienced compound tailing or streaking on your TLC plate or flash chromatography results and wondered what in the world is going on here? Well, there can be multiple reasons for this problem including poor mass-transfer kinetics, secondary solute-sorbent interactions, or unstable compound chemistry.

In this post, I will discuss one technique that has been shown to work time and time again to address the issue.

Continue reading When should I use a pH modifier in flash column chromatography gradient?

When should I use a “high-performance” flash chromatography column?

The evolution of flash column chromatography has brought chemists many new and exciting options for crude mixture purification. Among them are so-called high-performance flash columns or cartridges.  These high-performance purification tools are typically filled with silica or other media 15 to 30 microns in particle diameter (versus 40-63 micron for standard flash media) and provide the expectation of better separations and higher purity fractions.  That’s really enticing but how often do you need these types of columns especially since they are, of course, more expensive?  Well, that question is what I address below. Continue reading When should I use a “high-performance” flash chromatography column?

So, how does an ELSD work?

Evaporative Light-Scattering Detection, or ELSD for short, is a technology used with liquid chromatography to see UV-transparent (and UV-absorbing) compounds. In a previous post I talked about some applications where ELSD is not only useful, but required.

In this post, I will explain how an ELSD is configured and functions. Continue reading So, how does an ELSD work?