Using adducts and fragments to identify compounds in mass-directed flash chromatography

Over the past several years, automated flash chromatography has evolved to include in-line mass detection.  Typically, these single-quadrupole mass detectors are outfitted with either an atmospheric pressure chemical ionization source (APCI) or an electrospray chemical ionization source (ESI).  While this technical advance in flash chromatography has helped chemists detect and isolate pure compounds with a known molecular weight, verifying the identity of that compound can sometimes be a challenge as the detected mass may not match that which you expect due to fragmentation and/or adduct formation.

In this post I will offer some assistance in determining adducts and fragments.

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What impact do buffers have on APCI mass detection?

APCI (atmospheric pressure chemical ionization) and ESI (electrospray ionization) are the two most frequently utilized mass detection tools for automated flash chromatography.  In a previous post, I discussed differences between the two detectors and the compound types best suited for each source.

Because these two sources ionize differently, there are cases when additives are needed in the make-up solvent and cases when they should not.  In this post, I will show the impact that adding a buffer or acid has on APCI detection.

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Understanding silica – why matching TLC and flash silica is important for good flash column chromatography

Recently, I posted an article explaining why high performance TLC plates are not needed for method development for high-performance flash chromatography.  Based on some excellent feedback, I see a need to discuss silica chemistry and its impact on chromatography. Continue reading Understanding silica – why matching TLC and flash silica is important for good flash column chromatography

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.

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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.

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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