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Nothing Ever Lasts Forever
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We all know that nothing ever lasts forever. However, in chromatography terms, there are a number of ways that the life of a column may be shortened through unnecessary or accidental deterioration.
In this article I am going to briefly cover the most common causes of damage and what you can do to avoid them, possible restorative actions, and discuss a robust column type that you may be able to use in your analyses.
So, let's identify the five most common things that can lead to column deterioration:
- dirty samples - matrix contamination can deposit on the injector or on the front-end of the column and lead to tailing peaks and poor quantitative transfer
- very acidic or basic samples may damage the phase
- poor gas management - oxygen can degrade polar phases very quickly, especially traditional wax (or polyethylene glycol) phases
- incorrect storage - make sure the column ends are sealed and that the column is stored in such a way that the fused silica can't be damaged by contact with sharp edges
- overheating
Leading on directly from this, I have six tips to avoid damaging your column:
- do not heat the column until it is purged with oxygen-free gas (10 volumes - approx. 20 minutes)
- always note the injector and detector ends so that you do not accidentally connect the 'dirty' injector end to the detector, which would quickly transfer the built-up non-volatile material to the detector and lead to an increase in noise
- keep in mind the column phase and dimensions you are using as thicker films and more polar phases generally have lower maximum temperature limits
- do not overheat the column unnecessarily as this will shorten its life
- consider using a guard column and/or quartz wool in the liner, in order to trap any non-volatile material before it gets on to the column.
- support the column cage in the oven to reduce the possibility of column fracture
If you believe that your column has suffered some damage, there are a number of simple ways in which its performance may be restored. Firstly, try removing a small amount (50-100cm) of the column from the end nearest the injection port and then trying the column again. Secondly, try turning the column around, re-connecting it tot he injector but not the detector, and re-conditioning it overnight. Lastly, you can try washing the column with 2-3 column volumes worth of solvent. Go from a polar to a non-polar solvent (e.g.. methanol to acetone to hexane, etc.) but take care to ensure that all of the solvent has been removed from the column before reconnecting it to the detector. Be especially careful when washing wax columns with polar solvents, as this can wash some of the phase out of the column.
As an example of how re-conditioning a column can help restore it's performance, Figure 1 shows three chromatograms of a TRF C test mix on a BPX5 column. The first is a reference run, whereas the second demonstrates the effect that turning off the carrier gas and leaving the column for 2 hours at 300°C has. Note the disappearance of the decyclamine peak and the loss of phase evident in the reduced retention time. The third run is after a further 2 hours reconditioning at 370°C. Note the partial return of decyclamine and the noisier baseline due to silica deposits on the FID
After a further 6 hours reconditioning at 370°C, the decyclamine peak is back and we have a reasonable separation. However, the decreased retention times show that some of the stationary phase has been lost.
Conventional wax, or polyethylene glycol columns are easily damaged by exposure to oxygen at even moderate oven temperatures. In fact, all it takes is for the carrier gas cylinder to run out over lunch time and you will lose most of the phase, leading to very short retention times and very little resolution. Figure 3 shows the effect of turning off the carrier gas at 250°C on a SolGel-Wax column and leaving it to bake for 1 hour. As you can see, the SolGel-Wax column stands up very well to this maltreatment and, although some phase is lost, useful separation is still occurring.
If you have further questions, please send me an email or phone me on 01908 568844 quoting "0402".
Happy Chromatographing!
Anthony Addinall
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