Synthetic chemists continually seek ways to create novel compounds. Along the way they evaluate reagents, solvents, and reaction conditions giving rise to various reaction products and by-products.
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.
Flash chromatography is a standard part of an organic chemist’s workflow. It is utilized after most reaction steps in order to remove most of the generated by-products and excess reagents.
Scaling up reversed-phase flash chromatography methods is often necessary as reaction scale increases. This is especially true when other non-chromatographic purification techniques do not work or meet purity and/or yield needs.
The bane of organic synthesis for most chemists is purification rather than synthesis. Synthetic reaction mixtures are rarely devoid of impurities so some type of purification is necessary. Most often flash chromatography is used but for many chemists, it is less well understood than their chemical reaction and provides some level of anxiety.
In this post, I will summarize the five most important steps to creating a successful flash chromatography method and thus the anxiety associated with it.
This is an interesting question that I am asked from time to time. There does seem to be two camps in which chemists reside – one believing longer and thinner columns provide better separations and the other preferring shorter and fatter columns to do the same chromatography.
Which is right? That is a question I will try to answer based on my own data.
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.
For many chemists using generic linear gradients and even gradients based on TLC the purification results often are not selective enough to separate all of the compounds in their mix. This is especially true if your target has a closely eluting impurity. One method used to try and increase resolution is the use of an isocratic hold or gradient pause during purification.
In this post I examine the use of the isocratic hold to determine how well it works and when/if it should be inserted into a gradient method.
Have you ever run flash column chromatography with mass detection (Flash-MS) and observed the total ion current or TIC increase during the purification only to find that there was no discernible compound contributing to the effect?
In this post I discuss how I came across this issue and the solution I found to work.
Chromatography is a common tool of the chemistry laboratory, and most chemists involved in synthesis have a good idea how automated flash purification system work on the lab bench. However, knowing how to take purifications from the laboratory to a manufacturing environment is a different question altogether.
The products of organic synthesis are designed with specific functional groups in order to possess desired properties. Depending on the compound’s functionality, it can be neutral, acidic, or basic as determined by a compound measurement called pKa or acid dissociation constant. Compounds with low pKa are typically acidic while those with high pKa tend to be basic. Compounds with a pKa near 7 are deemed neutral.
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.
Our clientele at Biotage have interesting and diverse backgrounds from highly skilled synthetic chemists, to experts in natural product chemistry, to those who are just beginning they journey with chemistry. What I have learned over my 40+ year career in the “art” of chromatography is that for many of these fine folks there is a lack of understanding about chromatographic principles. This lack of understanding, I believe, is only due to their core study curriculum where separation science is used as a tool during lab work but the principles behind why a mixture’s components separate (or do not separate) perhaps are not effectively explained, understood, or studied.
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.
The challenges organic, medicinal, and natural product chemists face are many: from designing reactions, to optimizing synthesis, work-up / extraction, and purification / isolation of the desired compound or compounds. Among those issues related to purification / isolation is the common problem of separating compounds with similar chemistry that either co-elute or separate poorly.
In this post I will discuss some tips on how to "resolve" this issue (yes, pun intended).
Usually, a 2-solvent or binary gradient will separate your desired compound from the by-products and impurities. Sometimes though, you can encounter a mixture in which some compounds co-elute and are not separable with any binary gradient you try.
I encountered this situation recently while trying to purify a lavender essential oil and have dedicated this post to how I solved the problem.