Old capillaries

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What happens to capillaries when they are old?

How do we tell when the capillary can no longer be used and should be replaced?
Very good question! What we know in general is that although we like to think of fused silica as inert, it is not. Anything that comes into contact with the capillary surface might leave its traces there. Of course we do anything to prevent that as best we can by proper conditioning procedures but we all know that cleaning is rather difficult (my daughters think so for sure :wink: ). So we generally say that it is good to keep track of the history of capillaries, or at least be aware of them. Long ago when I started to apply CE in industry, I labelled my capillaries, numbered them and kept records, similar as we do for LC and GC columns. I've stopped doing that (it is not so easy to mark a capillary :? ). Now, I stick to one application per capillary and as they are relatively cheap, take a new one in case of doubt.
Of course, during method development you'll have different BGE compositions inside, components that maybe will not stay in the final composition. It is therefore good practice to check the final method on a fresh capillary.

Usually, capillaries break in use before they really get old. As long as the separation looks good and passes the SST, use it. Sometimes you do come over very old stock though, like in my last job when we closed down R&D and had to empty well-hidden cupboards. I found some capillaries of at least 20 years old. Some of them seemed OK, other lengths seemed very brittle. I guess it is the same as for your drinking glasses at home. They're all perfect, and then suddenly one day they seemed to have reached the end of life time and within a short time all break.

The best way to check on capillaries is the SST, which should be appropriate (I saw your other remark and will take it up in a next CE solutions issue, thanks!). If the system suitability test does not pass, and if you have tuned the cause down to the capillary, which is not blocked, try an extended rinse procedure first.
If you want a quick check whether the capillary is blocked, go to a low UV wavelength, where NaOH absorbs. Rinse the capillary with water, autozero, then rinse with NaOH. You should see the UV signal go up 30 - 60 s after you switched from water to NaOH (time depending on length and diameter). If not, the capillary is blocked. Try to rinse it backwards and see if that helps. If not, and if there is sufficient length, cut of a few mm from the end(s) and test again.

And, depending where you work, keep in mind that the capillary is probably much cheaper than your hourly costs to the boss...
/Cari
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