In this post, I will look at how the latest automated features added to certain rotary evaporators simplify time-consuming processes. In particular, I shall look at solid loading, a sample loading technique used in flash chromatography. Solid loading offers higher-resolution chromatograms than liquid loading, but the sample preparation step involving evaporation is time-consuming and involves several manual steps. For these reasons, liquid loading is often preferred as it is the simpler method, even though it lacks resolution compared to solid loading. However, the latest automated features added to rotary evaporators simplify the sample preparation process making solid loading a more viable and promising solution. Read on to find out the benefits solid loading offers and how automation can eliminate the disadvantages often associated with the method.

I recently predicted what 2023 would bring to chemists and the world of laboratories. One of those predictions was increased automation. In the real world, I have had various experiences relating to automation, and my feelings are mixed. I have embraced home automation, and I love the fact that I no longer fumble around in my garage to find the light switch – usually after I’ve banged my head and tripped over a box of discarded videotapes . A motion sensor now detects once I’ve entered the garage, and the light comes on immediately – voila, no more needlessly bumping my head in the dark. There are, however, other automated aspects of modern living that I cannot comprehend and don’t particularly relish; for example, I was doing the weekly shopping the other day, and my wife could not understand why I joined the queue to the checkout when I could use the self-scan machines. I still prefer the human interaction at the checkout and not having to figure out which variety of apples I haphazardly put in my basket! I always found the self-checkout machines to be quite paradoxical. If there is a long queue, you could save time; however, the number of manual steps increases. I would rather wait slightly longer in a queue and have someone far more competent than me handle all the weighing and scanning. When it comes to laboratory equipment, though, my experience with automation has always been positive. The technological advancements have often saved time and improved the accuracy of results, a win-win.

I wrote about the history of chromatography for a recent post celebrating this blog’s fifth birthday. The process has come a long way since its inception, and improvements are still being made to this day. For this post, I would like to focus on the process of solid loading. In liquid chromatography, a sample can be loaded in two different ways: solid or liquid . Liquid loading involves dissolving a sample in a solvent and injecting the solution directly into the cartridge or column. Samples that consist of a solid or crude mixture require solid loading, whereby the sample and support material, such as silica, are placed in front of the separation cartridge. Each technique has its advantages and disadvantages. Liquid loading is fast and relatively easy to perform; however, it only offers a low resolution. Solid loading is a more involved and time-consuming process but offers high-resolution chromatograms. Automation has improved both techniques over the years. Liquid sample injection is now done with a dedicated injection valve, which increases accuracy and safety, reduces the manual steps involved, and reduces the likelihood of contamination. The level of automation used for the solid loading technique has only recently been increased. Finally, the time-consuming sample preparation step can now be automated with the latest instruments , as well as the process of evaporating to dryness.

Solid loading is necessary for large samples that are difficult to dissolve. This approach reduces other methods’ band-broadening and ailing effects, offering improved resolution. Also, as my home automation stops me from bumping my head, automation can prevent bumping during the evaporation process on a rotavapor during the preparation of a solid loading mixture. Bumping, when talking about chemistry, is what occurs when liquids are heated and have their pressure reduced rapidly, causing large vapor bubbles that can cause the rapid expulsion of the boiling liquid. Automation of the pressure control aspect of evaporation helps prevent this phenomenon. Solid loading involves the following steps:

– Dissolving the crude sample in a suitable polar solvent.
– Incubating the mixture in an ultrasonic bath to enhance solubility.
– Filtering the mixture to remove undissolved material.
– Adding silica to the mixture at five times the weight of the crude sample.
– Evaporating the solvent to remove it.
– Packing the solid sample into a pre-column (solid loader).
– Loading the pre-column in front of the separation cartridge into the solvent flow.
– Eluting the components to be separated from the pre-column into the separation cartridge.

Due to the number and complexity of steps involved, solid loading is a prime candidate for increased automation. Thankfully, new features like AutoDest and AutoDry have automated one of these processes. The AutoDest function evaporates solvents automatically without the need to select a suitable system pressure. A sensor monitors the temperature of the inlet and outlet of cooling water to the condenser, and the vacuum pressure is adjusted accordingly. This frees up time for a lab technician like me as the process does not have to be monitored regularly. Nowadays, you can also add an AutoDry valve between the condenser and receiving flask. Whereas AutoDest reduces the evaporation solvent to a minimum, AutoDry evaporates the residual solvent to dryness quickly and without any interference from the user. The combination of these two additions to the traditional rotavapor setup results in the highest levels of automation for preparing samples for solid loading . The graph below shows the system pressure over the course of the automated distillation process.

It starts with a steady gradient to prevent bumping. Once condensation is detected at the cooling coils, the pressure is held stable. After 31 minutes (1860 seconds on the graph), the pressure is further reduced to maintain an ideal condensation level. The evaporation process ends automatically after 54 minutes.

After the automatic distillation process shown in the graph above, the drying process can also be automated. The system is vented to atmospheric pressure to promote condensation of the solvent. The condensation builds on the glass walls and flows into the receiving flask. A drying time is selected, and the automatic process begins, which includes two venting steps, promoting the downflow of the condensed solvent. Automating these processes makes solid loading far more viable, as the sample preparation process has been greatly simplified. As a result, the process is safer, easier, more efficient, more accurate, and more consistent. Although I have focused on how an automated evaporation process helps makes sample preparation for solid loading chromatography more viable, it is worth mentioning that the AutoDest and AutoDry features make all evaporation tasks easier!

I hope this look into the benefits of solid loading and how simplifying the sample preparation step by automating the evaporation process is useful to all those wishing to streamline and improve their workflows.

Till next time,