Welcome to the Biotage Flash Purification Blogs.

    Detecting the undetectable in flash column chromatography, part 2

    December 1, 2020 at 2:19 PM / by Bob Bickler posted in Chromatography Fundamentals, Troubleshooting and Optimization, Detector

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    Compound detection challenges are, for many chemists, a part of life. In a previous post I discussed how wavelength focusing can help your flash system detect and fractionate compounds with poor chromophores. However, compounds naked to UV-Vis light,  such as carbohydrates, are impossible to detect by UV when separating by liquid chromatography.

    There are some alternatives, however, and in this post I will discuss the application of evaporative light scattering detection (ELSD) to flash purification.

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

    November 25, 2020 at 4:34 PM / by Bob Bickler posted in Chromatography Fundamentals, TLC

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    Higher performance flash columns 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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    When should I add acid to my detector make-up solvent when using mass-directed flash chromatography?

    November 20, 2020 at 2:57 PM / by Bob Bickler posted in Amine, Chromatography Fundamentals, Reversed-phase, Solvents

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    Increasingly, organic and medicinal chemistry labs use mass-directed flash chromatography to isolate synthesized compounds. Mass-directed flash chromatography benefits are many, including collecting only the targeted molecule(s) in the reaction mixture. This approach simplifies compound purification since you know what you have made and it's associated mass.

    However, there are mass detection nuances that can be challenging. One of these is to know when an acid should be added to the mass detector’s make-up solvent to protonate targeted molecules. In this post, I will provide some insight on this topic.

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    In-line Scavenging Simplifies Flash Column Chromatography Reaction Mixture Purification

    November 20, 2020 at 2:55 PM / by Bob Bickler posted in Scavenger, reaction

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    I am always grateful for the feedback I get from my blog readers.  Today's blog is in response for multiple requests for tips on purifying complex mixtures and suggestions for alternative sample loading techniques.

    In this post, I will attempt to address both, to some degree anyway, with a single example using a scavenger resin.

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    Can reversed-phase chromatography compound elution volume/time be predicted?

    November 18, 2020 at 9:26 PM / by Bob Bickler posted in Chromatography Fundamentals, Reversed-phase, Method development

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    When developing reversed-phase flash chromatography methods it is important to understand the impact that a change in solvent ratio has on compound retention and, therefore, separation performance. Unlike normal-phase chromatography where you can optimize separations using TLC and a wide variety of solvents and solvent ratios, reversed-phase limits you to 3 to 4 solvents, including water, using either HPLC or small flash columns for method development. Those solvents include:

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    Invest 10 minutes on TLC and save a day of grief

    November 13, 2020 at 1:17 PM / by Bob Bickler posted in Chromatography Fundamentals, Green, TLC

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    Flash column chromatography is used by between 20 and 40 thousand organic synthesis chemists worldwide, an amazing number. For most of these chemists flash chromatography is an important part of their daily workflow but allocating time for good method development is often not considered, which can lead to less than ideal purification results.

    In this post I focus on how allocating just 10 minutes on thin-layer chromatography (TLC) for method development can save you a lot of grief later on.

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    Why is my UV baseline changing during flash column chromatography?

    November 6, 2020 at 8:15 AM / by Bob Bickler posted in Chromatography Fundamentals, Solvents, Media and Resin

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    A baseline that rises or drops when using flash chromatography with a UV detector can be a problem, especially if you are trying to collect compounds with poor detectability or that exist in low quantities.

    In this post I will talk about the causes and solutions for a rising (or even dropping) baseline.

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

    October 30, 2020 at 6:40 PM / by Bob Bickler posted in Chromatography Fundamentals, Troubleshooting and Optimization, purification

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    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.

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    Non-aqueous (or nearly so) reversed-phase flash column chromatography – a nice alternative for purifying lipophilic compounds

    October 23, 2020 at 5:25 PM / by Bob Bickler posted in Chromatography Fundamentals, Reversed-phase, purification

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    For most organic and medicinal chemists, normal-phase flash chromatography is used to purify and isolate many types of organic compounds, most with some polar functional groups which help them retain on silica. However, some compound mixtures are water insoluble such as lipids, carotenoids, terpenes, tocopherols, polyaromatic and other hydrocarbons with minimal polar functionality.   These lipophilic compounds do not retain well on silica and do not dissolve readily in water making them really difficult to separate.

    In this post I will talk about a technique called non-aqueous reversed-phase chromatography that can be very effective at separating and purifying very lipophilic compounds.

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    How Can I Speed-up My Synthesis Workflow?

    October 20, 2020 at 2:04 PM / by Bob Bickler posted in Scavenger, V-10, Extraction method optimization, microwave, purification

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    Wouldn’t it be nice if your reactions only created your desired product? Of course the answer is yes, but that is not the reality of synthetic chemistry. Because our chemical reactions yield multiple components, they need work-up and purification to isolate the desired compound.

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    Ionizable compound purification using reversed-phase flash column chromatography

    October 16, 2020 at 4:54 PM / by Bob Bickler posted in Chromatography Fundamentals, Solvents, Media and Resin

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    With most chromatographic purifications, only two solvents are needed to adequately separate compounds from each other. Unfortunately, there are instances where the separation is either poor or cannot be accomplished with “normal” elution conditions such as those with ionic or very polar organic molecules.

    In this post I offer some solutions to this issue.

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    How best to extract reaction products from high boiling solvents

    September 22, 2020 at 2:23 PM / by Bob Bickler posted in Solvents, Workflow, Extraction method optimization

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    Organic chemistry syntheses often use polar, high boiling point solvents to facilitate high temperature reactions. However, these solvents also can complicate down-stream compound purification, either by evaporation, crystallization, or even flash chromatography.

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    How can flash chromatography UV absorbance spectra be used to identify purified compounds?

    August 25, 2020 at 1:52 PM / by Bob Bickler posted in Chromatography Fundamentals, UV, Spectra

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    As chemists, our job is to make new molecules. If our synthetic design works as planned, we will have success and the target product made. As we all know, along with our desired compound, by-products are often created as well. To remove the by-products, the reaction mixture requires purification, typically with flash chromatography.

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    How should I purify a complex, polar, amide reaction mixture?

    August 12, 2020 at 1:46 PM / by Bob Bickler posted in Amine, Chromatography Fundamentals, ION exchange

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    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.

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    How do I convert my HPLC method to flash chromatography?

    July 14, 2020 at 2:00 PM / by Bob Bickler posted in Chromatography Fundamentals, Reversed-phase, HPLC

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    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.

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    Can reaction solvent choice impact synthesis results?

    June 30, 2020 at 5:21 PM / by Bob Bickler posted in Synthesis, microwave

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    Most chemical reactions take place in liquid form since compounds in solution are more likely to interact with each other, especially when heated. Reaction solvent choice varies based on reagent solubility and reaction temperature requirements. Because many reactions today require high temperatures, solvents such as dimethylformamide (DMF) and dimethylsulfoxide (DMSO) are frequently used. However, just because a reaction solvent has the proper reagent solubility and/ or a high boiling point does not mean it should be used. Why? Well, as we will show in this post, the solvent itself can alter synthetic efficiency by changing reaction kinetics as well as the number and type of by-products.

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