Why does my silica flash chromatography column get hot?

Silica is the most commonly used sorbent for flash column chromatography. When solvent is pumped through a column packed with dry silica you may notice it gets warm and sometimes down right hot!

In this post I will attempt to explain why this phenomena occurs. Continue reading Why does my silica flash chromatography column get hot?

Why is TLC Rf important for flash column chromatography optimization?

Many chemists I talk to understand that TLC data is useful for flash chromatography method development. Most also know that they should try to get their target compound to elute with an Rf between 0.15 and 0.4 by adjusting TLC solvent strength. Have you ever wondered why this is important and how Rf values impact flash chromatography results?

In this post I will explain the relationship between TLC Rf and flash elution volumes (CV) and why having your target compound elute in the Rf range is needed. Continue reading Why is TLC Rf important for flash column chromatography optimization?

Determining solvent strength in flash column chromatography

Recently, one of our readers wrote and asked how to determine solvent strength in normal-phase flash chromatography. This is an excellent question because solvent strength is one of several factors impacting flash chromatography performance.

In this post I will explain how solvent strength can easily be determined. Continue reading Determining solvent strength in flash column chromatography

Are reversed-phase flash chromatography columns designed for aqueous solvents necessary?

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.

In this post I explore if these types of phases are actually needed by looking at the separation of some very polar and low log P compounds using a “traditional” C18-bonded silica.

Continue reading Are reversed-phase flash chromatography columns designed for aqueous solvents necessary?

How does solvent choice impact flash column chromatography performance?

Selectivity and solvent strength are the most important factors that determine success or failure of a chromatographic separation. These two independent dynamics apply to both normal- and reversed-phase chromatography and should be optimized, especially when high fraction purity is needed.

In this post I will discuss the impact that elution solvent choice has on both normal- and reversed-phase purification. Continue reading How does solvent choice impact flash column chromatography performance?

Are there advantages to stacking flash chromatography columns?

When it comes to isolating a compound from a mixture at maximum purity there are many options available through flash column chromatography. In previous posts I have addressed using smaller particle media, higher surface area media, and step gradients to achieve this goal.

In this post I will discuss how stacking columns in series may help improve separation quality. Continue reading Are there advantages to stacking flash chromatography columns?

How does media pore size impact peptide resolving power?

Purification by reversed-phase chromatography relies primarily on a hydrophobic interaction of the molecule with the alkyl chains bonded to the stationary phase for column retention and elution through a partitioning mechanism.  While this is certainly true for purification of peptides, surface area accessibility and media particle size also play critical roles in the resolving power of a particular stationary phase.  The particle size influences the loading capacity, however pore size greatly influences molecular accessibility and therefore resolving power.

In today’s post, I will demonstrate how pore size can impact your peptide purification using flash column chromatography.

Continue reading How does media pore size impact peptide resolving power?

In-line mass detection to find the undetectable in flash column chromatography

In previous posts I have discussed some options and techniques to improve detection of poorly absorbing or UV-transparent compounds – by wavelength focusing and by evaporative light-scattering (ELS).

In this post I will talk about a third alternative technique – using an in-line mass detector. Continue reading In-line mass detection to find the undetectable in flash column chromatography

Benefits of acetonitrile over methanol in normal-phase flash column chromatography

When it comes to the purification of polar organic compounds many chemists turn to normal-phase flash chromatography with dichloromethane and methanol as the mobile phase. This solvent system often can be challenging to optimize due to methanol’s high polarity and protic chemistry.

I have found that acetonitrile can often replace methanol as the polar modifier in DCM-based solvent systems.  In this post I will show an example where this is true. Continue reading Benefits of acetonitrile over methanol in normal-phase flash column chromatography

Pushing flash column chromatography loading limits

A question I hear a lot from chemists is “how much can I load”. The answer is always “it depends on your separation quality”.  At that point I begin asking about the TLC data and purification goals. Purification goal setting should be your first step and the question to answer is – what do I need this purification to achieve? Is the goal high purity, high yield, or some combination.  Remember, you will typically sacrifice purity for high yield and yield for high purity so optimization is an important consideration.

In this post I will discuss the results of a study I conducted where I continually increased the crude sample load until my target compound purity fell below specific targeted levels to understand the real loading limitation. Continue reading Pushing flash column chromatography loading limits