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.
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.
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.
Biotage has developed ACI™ Accelerated Chromatographic Isolation, a revolutionary advancement, converting regular flash from simple purification to the fastest, greenest, and most economical way to reliably isolate pure compounds for organic synthesis. ACI is 2–3 times faster than flash, more efficient than flash and with 100–1000 times the typical capacity of preparative HPLC. ACI is not just a speed setting on an instrument panel; ACI embraces higher system flow rates and the use of smaller particles in chromatography. ACI also makes use of intelligent gradients, patented TLC-to-step gradient procedures and an intelligent patent pending algorithm to allow equilibration of highly polar solvents.
To support this, many important changes were needed to the framework and thinking behind a regular flash system. It was also clear that not just any flash cartridge will be able to provide all of the features of ACI. SNAP Ultra was developed a while ago with the longer term strategy of ACI in mind.
SNAP is the name of Biotage’s proprietary plastic column, containing a removable plastic insert that can be used to dry load the column or as a void ready for liquid loading. 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 with 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 column, 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.
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 between twice and 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.
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.
Biotage’s focus and commitment to flash purification and the needs of the synthetic chemist have helped us to develop tools that maximise the power of chromatographic purification and focus on the key drivers for purification chemists.