Welcome to the Biotage Flash Purification Blogs.

    Why Reusing Flash Cartridges is Bad Science

    December 14, 2020 at 10:08 AM / by Bob Bickler posted in Reuse, silica

    0 Comments

    For many chemists lab budgets, especially for consumable items, are limited.  One way of trying to stretch their lab budget is to reuse disposable flash chromatography cartridges.

    In this post I will show how regardless of the cartridge brand used, repeated use of silica flash cartridges results in loss of compound resolution and fraction purity.

    Read More

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

    December 11, 2020 at 2:04 PM / by Bob Bickler posted in mass detection

    2 Comments

    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.

    Read More

    Using pH to optimize reversed-phase flash chromatography separations

    December 8, 2020 at 8:51 PM / by Bob Bickler posted in Chromatography Fundamentals, Reversed-phase, Solvents, Media and Resin, Detector

    0 Comments

    I have previously posted on the topic of normal-phase optimization by evaluating different solvent blends or mixtures. I have also touched on reversed-phase method development as well suggesting chemists use HPLC to optimize their purification.

    In this post, I will look at the impact modifying mobile phase pH can have on reversed-phase separations.

    Read More

    Does mass detection make-up solvent choice matter?

    December 7, 2020 at 4:18 PM / by Bob Bickler posted in Solvents, mass detection

    0 Comments

    An interesting question, at least to me. Depending on the detector brand, some mass spectrometer manufacturers recommend acetonitrile while others recommend methanol. Is there a real difference between these solvents?

    In this post I look at how acetonitrile and methanol compare when used with an APCI source.

    Read More

    Can reversed-phase flash column chromatography be greener?

    December 3, 2020 at 7:24 PM / by Bob Bickler posted in Reversed-phase, Green

    5 Comments

    In previous posts I offered some suggestions to improve the “greenness” of normal-phase flash purification.  As the use of reversed-phase flash purification has increased the past few years I thought I would explore how to potentially make it greener too.

    So, with that in mind, let's take a look at the use of acetone in place of acetonitrile as a reversed-phase flash chromatography solvent.

    Read More

    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

    0 Comments

    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.

    Read More

    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

    3 Comments

    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.

    Read More

    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

    1 Comment

    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.

    Read More

    In-line Scavenging Simplifies Flash Column Chromatography Reaction Mixture Purification

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

    6 Comments

    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.

    Read More

    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

    0 Comments

    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:

    Read More

    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

    0 Comments

    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.

    Read More

    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

    2 Comments

    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.

    Read More

    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

    2 Comments

    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.

    Read More

    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

    1 Comment

    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.

    Read More

    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

    0 Comments

    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.

    Read More

    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

    5 Comments

    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.

    Read More