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.
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.
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.
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.
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.
Flash purification is a preparative liquid chromatography technique. As such, it incorporates the same types of components as preparative high-pressure liquid chromatography (pHPLC) – pump, gradient mixer, column, UV detector, and fraction collector. Though all flash chromatography systems are purpose-built and essentially work the same, the one area of difference is in the UV detector design and operation.
Are you observing more chromatographic peaks than you expect compared to TLC or other assessment data? Well, it could be that your method is separating some isomers or, it could be that there is an actual method issue.
In this post I will discuss what could cause a method issue and suggest some ideas as to how to fix it.
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.
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.
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.
In a previous post I talked about column size, specifically long-thin versus short-fat and the impact of the cartridge’s dimensions on purification performance. With that comparison I showed that in preparative chromatography, purification efficiency is more about the amount of silica than column dimensions. Cartridges of different dimensions containing the same amount of the same media will provide the same separation efficiency.
Yes, the title is a bit salacious but it got your attention, didn’t it? I believe this is a topic worthy of discussion as it relates to flash chromatography for purification because many chemists believe longer but thinner columns perform better than short, wide columns. The facts of the matter may surprise you.
In this post I discuss the impact that cartridge dimensions have on purification performed using flash purification.
In my role as senior technical specialist at Biotage I am often asked about compound detection options. For most flash chromatography methods, UV is the default detection tool since many compounds do absorb some UV light.
Diode array UV detectors provide chemists choices in wavelength selection providing the ability to widen or narrow the wavelength range needed to detect specific compounds and enhance their sensitivity.