Chromatography Forum

Hi,

We have a student wanting to analyze Tinosorb M (UV absorber in sunscreens), and it appears as though we may not be able to avoid the use of THF.

I've read of the compatibility issues with PEEK tubing and how it is best to re-plumb with stainless steel tubing. As we won't be running the Tinosorb M method often, I wondered if we would be able to get away with replacing the PEEK tubing at various time intervals rather than replacing it with stainless? It is the flexibility of PEEK that appeals. I'm concerned especially with the tubing-to-flow cell connection. If (more rigid) stainless were substituted for the PEEK, there would be increased force at that connection when the column is moved. Could the flow cell connection crack, or am I just being paranoid?

Thanks!

Flow cell bulk head fittings are usually pretty robust.
If you are just using a small percentage of THF in the MP, you can probably get away with it, after all - if it goes wrong, replacing some PEEK is not a big deal. Also, as long as you're using it in low pressure areas, you should be OK.

There's more on PEEK in John Dolan's "HPLC Solutions" blog:
http://tinyurl.com/6o6pok9

Thanks guys!

We could be running up to 20% THF and all connections between modules (pump, detector, autosampler etc) are PEEK. If it weren't for the difficulties with stainless tubing I wouldn't be thinking twice about the conversion, which says to me I must do it.

Have been also reading about stainless steel tubing cutters, and people's comments about buying precut lengths. Some companies offer cutters for "non-critical connections" but don't explain what that means. Is it babble for cutter can cause some burring, or does it mean it can be used for connections that use a ferrule?

Stainless steel is not all that bad to work with. Precut lengths are *definitely* the best.

The conventional rotary cutters and the "nippers" both leave some roughness at the end and don't necessarily make a clean perpendicular cut. For "conventional" HPLC columns with id's in the 4 mm range, a microliter or so of extra-column dead volume isn't really a big deal but for "UHPLC" columns with id in the 2 mm (or lower) range, even that small a cavity can have an impact on efficiency.

The high-speed rotary cutters like this one make a nice perpendicular cut, but you have to go back and ream out the internal diameter. I like it, but the price tag is hard to justify unless you're cutting a *lot* of tubing!