Problems with tubing

[Coffman]

I am a grad student who is trying to learn how to use an HPLC with little help and no service contract.

Currently, I am experiencing some various problems and while getting to know the machine I'm stuck with, I see that one of the SS tubes coming out of the column seems to be in bad shape on the end. While the tube going into the column looks nice and round and flat, the one coming out of the column looks scratched and corroded on its end. From what I can see with a handlens, it doesn't look as if the hole is even, it looks like its smaller than the other one, and doesn't seem to be entirely round. So I am feeling like the tubing needs to be replaced.

So I have a few questions:

1) Is there a way to tell the ID of some tubing other than measuring it under a microscope?

2) What's the best practice on tubing diameter? I seem to have larger ID tubing going into the column and smaller ID tubing coming out of it (though maybe just the end is messed up)

3) We have a SS tubing cutter, but everything I read online says not to cut your own tubing. Is it really so hard?

Thanks,
Clayton

[marc_foster]

by eye under the microscope is probably your best way. You can also buy piano wire that is just under the common ID's.

You can try cutting your own tubing but I doubt you will get a clean cut. You can flatten your cut with some emory cloth.

Smaller ID on the end is useful to preserve your peak shape. Not as critical on the front end but can affect your gradient.
I would suggest 0.010 tubing for a 4.6 mm column.

[tom jupille]

In addition to Marc's suggestions, you might take a look at using PEEK tubing. You can cut it with a razor blade, and it's color-coded so that there is no ambiguity about diameter.

Downsides are that it has some solvent compatibility issues (not recommended for THF, for example), you have to use PEEK nuts and ferrules with it, and you have to be more careful connecting columns (make sure that the tubing is pressed all the way down into the fitting).

[DSP007]

Good afternoon.
Warning.
Before you climb to the technique of the repair. Must be sure that there are all tools and understanding how it should be. It is also important to "hand did not grow out of ass." If you are not sure - ask the elders. Not a fanatism with a wrench - biggest effort to break (destroy) the nut easily. Though it often err woman. If nut do not go, then should not go.

Now on the subject matter.
The smaller the internal volume of the system - the better. From this perspective, thin tubes or short pipelines, well. But all the more difficult to mount neatly. Assembly of the thick tube takes 10-15% efficiency of the column - for many tasks - it does not matter.
Regarding state of the tube is not very critical. If you see rust, and you can unscrew the pipe - try to remove and wash (passivating) tube in 67% nitric acid. Be at the same time careful not to make keratin reaction from your skin.
The tubes are cut a special tool, but with some good skill and finishing bench .

Now about the tubing (fitting) - with the old piping is preferable to use PEEK even steel pipes - they are crimped accurance . Stint with THF was mentioned for you .

Well good luck with your repair.

[lmh]

Get hold of the catalogues from manufacturers such as Phenomenex. Most will advise you on suitable diameters for different flows, and suitable materials for different solvents. For example, then 10/11 catalogue from Phenomenex has a table on page 369 comparing flow-rates, column-dimensions, and most suitable tubing diameter.

Fatter tubing out of the column will lead to peak-broadening and poor resolution (it's easier for material to diffuse further from where it ought to be). Thinner tubing will increase back-pressure at higher flows (so you can't just fit the thinnest you can buy).

Yes, you can use PEEK provided your solvents are compatible with PEEK, and it's easier to cut (though you should use a proper cutter for PEEK, and not a cutter for SS tubing; the two have different cutting tools; incidentally, Tom's suggestion of cutting it with a razor blade: yes, but you need steady hands and a good judgement if you're going to cut it square. Most people use a specially-guided blade tool). Tom's right that you must fit columns to peek with care, making sure that the tube is pushed into the column's seat as far as it can go. However, stainless-steel swaged fittings aren't problem-free either. The geometries of the fittings vary from manufacturer to manufacturer, so if someone swaged your SS fitting for a Waters column, you may get into trouble if you change to using a different manufacturer's column. With Peek there is no such problem.

[Coffman]

Wow all this is great, I'll look into all of it!

[mwoodman]

Let me add a few bits.
You are having some problems and I hope to hear those problems in future posts. Just because your tubing looks ugly does not mean it is part of one of your real problems. It may only be a distraction.
People have cut tubing by hand for years. Circular cutters score the perimeter (perhaps as deep as 20% of the diameter) and then use fingers (for PEEK) or two smooth jaw pliers for stainless. You will get the most square end this way. Nicking one or multiple sides of the ss and bending it to break often creates a crooked end but improves with practice. PEEK sliced through by a blade, guillotine style, is often crooked and/or there is a flap of PEEK crossing the hole that interferes with nice straight flow.
Modern technology for cutting tubing can produce very high quality square end cuts, but at a price and the time required to order and receive the tube. Consider how urgent you need as well.

The i.d. and length of tubing contribute proportionately to the column efficiency. Small columns (2.1x50mm) are 15x more sensitive to tubing and fitting quality than 4.6x150mm columns. Consider that(your column dimensions) as you agonize over exactly what i.d. you should use or if you should stretch a connection to save a few cm of tubing length. Unless you plan to run flow rates over 1.5ml/min there will not be much pressure from "standard" LC tubing. I would say that most LC systems are plumbed with 0.005" i.d. (0.127mm) up to 0.009" (0.22mm). With 0.1mm and smaller i.d. you will experience pressure difficulties anywhere up to 1ml/min. The smaller diameters, often fabricated from PEEK-clad fused silica tubing, are normally reserved for specialized systems like capillary and nano scale separations. The volume saved by extreme choices is rarely justified -- given all other sources of dispersion in the system (flow cell of detector, volume of injection, quality and proper fit of tubing in connectors, number of tubing connections, etc.). And thank you to those who earlier explained that fittings of different vendors make look similar but not be the same. You can find diagrams with dimensions at quite a few web locations. For starters, look at http://www.postnova.com/PDFDocuments/pr ... gsbook.pdf (I do not work for Upchurch).

Good luck.