Leaky connections: what am I doing wrong?!

[Amesy]

I've been running HPLC off and on for awhile now, and I have a persistent problem that I'm hoping someone can give me some tips about: Every time I change columns, guard columns, or whatnot, at least one of the connections leaks. Usually it takes several attempts to assemble everything so that it doesn't drip. The system uses Peek tubing with the exception of the connection between the column and the detector, which is made of stainless steel. Any tips or tricks are appreciated!

[zokitano]

Which connection mostly appears to leak? The PEEK precolumn connections or the stainless steel postcolumn connection?
Which brand of HPLC system you're using? And which brands of HPLC columns?
I had a problem with leaks particularly with the stainless steel tubing of the HPLC Agilent 1100 when I tried to connect it on Waters column. It seemed that the stainless fitting was to short to enter the inlet holder of the column. That's why I changed the stainless tubing with finger-tight PEEK tubing and the problem was gone.

Best regards

[DR]

I have found that with most any finger-tight fitting, an 1100's column inlet tube is too well polished to maintain a seal above ~120Bar, so I use a file to rough up the outer surface of them just a little bit (be very gentle). It has helped a lot.

In general, if you find that new PEEK fittings are not a problem the first time you use them but leak thereafter, you're probably overtightening them. They should be made good and snug, but no tighter than the lab's 98lb weakling could make them.

[Amesy]

Which connection mostly appears to leak? The PEEK precolumn connections or the stainless steel postcolumn connection?
Which brand of HPLC system you're using? And which brands of HPLC columns?

The stainless steel connection between the column and detector is the biggest headache.... But, occasionally the PEEK precolumn connection into the guard column is also prone to leak (ugh!). We're using a Waters HPLC system with either Alltima or Agilent RP columns (column brand doesn't seem to matter -- the postcolumn connection always leaks the first time I attach it!)

[Consumer Products Guy]

Make sure when using hand-tight/fingertight fittings that the tubing is pushed through the ferrule sufficient distance, and push the tubing into the fitting and hold it there while you tighten it. It seems like it takes three hands, but you can do it. When replace one of the lines (Agilent), we use fingertights instead of the supplied metal ferrules/nuts on the end that attaches to the column. I believe we mostly use Upchurch Fingertight II, from Grace-Alltech, which uses a separate nut and ferrule.

[Consumer Products Guy]

And we can go up to 300+ bar, no problem.

[zokitano]

Dear Amesy,

If you have persistent problem with your stainless steel postcolumn connection, than I would suggest you to change it with PEEK finger-tight connection. Finger-tight fittings are suitable for use with different columns and different column holders. As DR previously said try not to overtighten the fittings.

Regarding your precolumn connection (tubing), see if its fittings are well and not deformed. If there is a problem with them also try to change them with new, or if they seem to be ok, try the suggestion from DR.

Good luck

[LC_labrat]

I've had problems with the peek fittings if they aren't centered correctly and tightened. This causes the threading on one side to be crushed. And inevitably leaks. Over-tightening can do the same thing.

[Dan]

Amesy,

When changing columns there are two concerns for avoiding leaks: having the correct fittings and keeping the fingertight fitting seated properly.

CPG already mentioned about using the fingertight fittings seated. I agree, sometimes it seems like you need three hands to get it right, but it can be done.

Using fingertight fittings helps to avoid the problem of mis-matched fittings. Some fittings are longer with more threads and they will work for most any column. However, the shorter fittings with fewer threads will not seat properly in some columns. It is all a bit of matching things up to the column end-fitting design to avoid leaks. Column end fittings vary by manufacturer.

A picture is worth a thousand words. So contact Upchurch for the great fittings guides that they give out free of charge. This info will give you the complete story (with pictures). These guides have helped me out over the years.

Regards,
Dan

[Amesy]

Thanks for all the helpful responses!