How to Make SPE Work Properly
Many labs struggle to get Solid Phase Extraction to give decent results.
So when the time comes to re-develop a method, they often decide to try-out SPE instead.
SPE promises lower solvent consumption. Also, one analyst and a vacuum manifold can process a whole batch of samples in parallel, so it should be much more efficient. The snag is that whereas LLE is relatively easy to get right, SPE is a multi-stage technique, many of these steps are critical and unless every sample is treated exactly the same, results will vary.
So, often, after much effort and frustration, the analyst returns to LLE because, despite its drawbacks, LLE does a pretty good job. Solvents like dichloromethane are very efficient extraction media and the technique is simple to master.
There is, of course, nothing inherently wrong with SPE.
It can be made to work well provided you…
- Throw the vacuum manifold in the bin.
- Take the trouble to lock down the critical parameters.
Automate the whole process.
SPE isn’t the problem – Humans are.
Here in the Anatune applications lab, we have just completed a project to develop a fully automated method for the solid phase extraction and analysis of NDMA and metaldehyde in potable water. This has been a tough nut to crack, but with the project complete, I have just had the chance to read through the final application note and one thing that stands-out a mile. The data is very good indeed.
If you follow this link to the application note you will see what I mean.
So what’s special about this approach?
1. The whole preparation and analysis is automated from end-to-end.
2. We are using an Agilent 7000 GC-triple quad. For our target analytes, this gives excellent S/N.
3. This, in turn, enables us to miniaturise the SPE.
4. Scaling down the SPE means it works faster.
5. This in turn means that we can prepare one sample while the previous sample is being analysed.
6. This means every sample is treated exactly the same.
7. This means the results are very consistent.
8. No humans are used in the process.
The final point I want to make is this:
The instrumental configuration we have assembled here has the potential to be a general purpose tool for the automated SPE-GC-QQQ analysis of lots of different suites of compounds in water. We can do a lot more useful work with this set-up.
What application can we investigate for you?
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