This article touches on the latest development in purification, ACI™ Accelerated Chromatographic Isolation, and how future needs of the typical Flash user will be met; way past the current limits of traditional flash. Flash evolved.
Flash purification is a chromatographic technique developed with one goal in mind – to deliver the maximum amount of purified product in the minimum amount of time. Many different scientists use Flash, but if there was to be a ‘standard’ user of Flash it would be a synthesis chemist who measures success on the basis of the number of pure compounds they can synthesise in a given time period. This runs at odds to the majority of users of chromatography, who are developing methods to allow them to identify trace amounts of specific compounds in complex matrices.
Flash Chromatography Versus HPLC
Every chemist leaves University with an understanding of HPLC (and its newer cousin UPLC), and this technique has become ubiquitous in analytical laboratories around the globe. HPLC is a technique that allows the resolution and quantitation of complex mixtures into component parts, and with the aid of information-rich detectors such as mass spectrometers allow the identification of resolved species.
In an analytical environment, the key parameters for users of HPLC are resolution and peak shape – analysts need to know that they have separated each component of their mixture, and sharp peak shapes help them to feel confident they have done so. In contrast, Flash chromatography is a purification technique. Users are attempting to isolate typically a single reaction product from a synthesis at the expense of other species present. For these chemists, the key drivers are loading and speed – they want to maximise the amount of their target compound they can isolate, and perform that isolation in the shortest time possible.
Unlike their analytical counterparts, instruments for synthesis chemists are merely tools that allow them to get back to doing what they do best – making compounds – as soon as possible. For the analytical chemist, the technique of chromatography is a discipline in itself. Although Flash and HPLC are both forms of chromatography, the key parameters and ultimately the aims of the processes are quite different.
ACI: The Future of Flash Purification
ACI™ Accelerated Chromatographic Isolation, developed by Biotage, is an advancement which converts regular flash from simple purification to a fast, green, and economical way to reliably isolate pure compounds for organic synthesis. ACI is up to three times faster than standard flash chromatography, more efficient, and processes 1000 times the typical capacity of preparative HPLC.
It is important to understand that ACI is not just a speed setting on an instrument panel; it is rather the sum of a number of factors which embrace higher system flow rates and the use of smaller particles in chromatography. ACI also makes use of intelligent solvent gradients, a patented TLC-to-step gradient procedure and an intelligent patent pending algorithm to allow equilibration of highly polar solvents.
Accelerated Chromatographic Isolation itself is a new concept in purification – combining the high flow rates that can be achieved with modern, well-packed columns and a proprietary equilibration procedure. Using ACI, flow rates are up to three times as fast as traditional flash, greatly reducing the time taken for a separation. Thus an ACI system could be made to run flash, but a regular flash system cannot be an ACI system.
Increased flow rates of ACI compared to flash across the Biotage cartridge range
For example, 250 mg of a compound can be purified on a 10 g column in three minutes. The new equilibration procedure perfectly wets the column even at very high polar solvent content, reducing heat of hydration issues that affect many flash equilibrations under these conditions.
Cartridge Performance is Key
In developing ACI, many important changes were needed to the framework and flash system design. It was also clear that not all flash cartridges will be able to support all of the features of ACI. Since cartridge performance is key to the result in ACI, Biotage® SNAP Ultra was developed a while ago with the longer term strategy of ACI in mind.
SNAP Ultra is packed with Biotage’s 25 um spherical flash silica, a low particle size packing that has superior resolution to conventional silica. This material is suitable for Flash as the lack of fines results in a very uniform packing giving a stable, low-pressure bed, and so – unlike low quality silica – despite the reduced particle size, high pressures are not required to run the column. But as we have discussed, for your average flash user resolution is not always of paramount importance. So, SNAP Ultra conveys another advantage over columns packed with standard irregular silica – almost twice the surface area, which equates to almost twice the loading of a more conventional material.
The real benefit of SNAP Ultra is that you can achieve the same purification loading and performance using a column half the size and at twice the speed. For example if a user had optimised a flash purification on a 50 g irregular cartridge, the same results would be obtained on a 25 g SNAP Ultra. Half the column size means that half the volume of solvent is required, which lowers the cost of purchasing and disposing of the solvent and also results in more concentrated fractions, meaning less time in sample work up.
Increased capacity of the SNAP Ultra columns means lower solvent consumption and less fractions.
SNAP Ultra is a key step in the process of maximising the potential of purifications by pushing the loading that is possible on a column to the limit, meeting a key driver of flash users. Both SNAP Ultra and ACI represent major advances in compound isolation, and significantly improve the speed and capacity of purification, the graph below shows just how much better ACI can be compared to regular flash purification.
Conversion of a Flash method to ACI results in drastically reduced purification time with no loss of resolution.