Troubles with press fit connectors...can't connect...

[Tommy Krak]

Good day All,

If you can spare the time and if you have some guidance for me.

I have tried many time over to make a good connection. I am monitoring for argon (high res. mass spec.) it looks like my connection is good and then I cycle the oven and the argon peak intensity increases significantly.

In my opinion my column cutting is really good. I am trying to use the Siltek connectors.

Does anyone have any tips for using glass connectors?

Cheers,

Tom

[chromatographer1]

www.chromtech.com.au/pdf/Siltek%20Deactivation-2001.pdf

The press-on connectors seal by using the polyimide coating on your column.

You must first soften and make this coating 'sticky'.

Make a clean cut.

With a Chemwipe or other clean paper or cloth, wipe down the last inch or two of the column with methanol or acetone toward the end of the tube.

Soak the last inch or so of the tube in methanol or acetone.

Using one steady for firm motion, push the tip of the tube into the connector and hold for several seconds, continuing to put gentle pressure into the connector with the tube.

You should see a ring appear around the inside of the connector where the polyimide has 'melted' onto the interior surface of the connector. DO NOT TUG on the tube in a direction away from the connector. Allow to dry for several minutes. If you have polyimide glue available from sundry vendors, push glue down into the connector around the column/tube and allow to dry. Once heated the polyimide seal (ring) will become fixed and you should have no other issues, especially if you additionally use the glue to hold the tube in place.

best wishes,

Rod

[Tommy Krak]

Thank you very kindly Rod for your response.

I believe that I am doing everything as you have outlined, this is why I am so baffled by my lack of success. I have read that these connectors can be difficult to use.

Cheers,

Tom

[chromatographer1]

The polyimide glue should not be permeable.

Perhaps there is another leak in the system?

There are other connectors you can try. From Restek, Supelco, and VICI, which use graphite ferrules to seal using metal unions. Restek's can be purchased deactivated and whatever size of column they can be butt-connected without metal narrowing of the bore.

While not for MS use, with the press-connects I have had great success. The other kind should be good for any purpose, even Mass Spec.

best wishes,

Rod

[Peter Apps]

Hi Tom

As I am sure you know, the most critical step is to get a clean square cut at the end of the column, which can be tricky. Are you inspecting the cut ends with a magnifier ?

How are you doing the cut - ceramic wafer, fancy rotating cutter, some other way ?

When you say that you are monitoring argon, are you spraying argon around the connectors, or is argon one of your analytes ?. If you are using helium or hydrogen as carrier can you detect leaks with a leak seeker ?.

How hot does the oven get when you cycle it ?

Peter

[Don_Hilton]

Manufacturer of press fit and of columns makes a difference. I have encountered some brands of press fit that do not seem to work well and I have found one or two columns that just do not make a seal. The column you may have to deal with, even if it is the problem. But you can try pressfits from a different manufacturer and see if they work better for you.

There is a company out there than makes a fitting that you melt onto the column joint. This is a bit of a step up in cost, but looks lie a good solution. Goodgle meltfit and you will find leads to NLISIS.

[DR]

I agree w/ most of what Rod has to say on this...
Personally, I never resorted to using glue. Warming both the glass union and column tips can be helpful.

Super Helpful: A 10x jeweler's loupe.
Use this little magnifying glass to inspect your cuts before trying to press-fit anything. I bet you find that not all of your cuts are equal.
Once you think you have made a connection, use it again to check the seal all the way around.
Also - I find that the cheap (or free, depending on who your column vendors are) ceramic wafers are far better for cutting columns than nippers, diamond tipped pencils etc.

[chromatographer1]

I agree with DR about the cutting and inspecting.

The sapphire stone cutters that Supelco offers, and the wafer cutters that Restek has are the best options IMHO. Supelco also has the wafers but I can never find them in their catalog, but that is my problem, your mileage may vary. The sapphire gemstone pens last a long time, the wafers not as long, but they are cheaper. take your pick. The wafers are also great to cut tiny 1mm and <1mm SS tubing.

best wishes,

Rod

[jdezeeuw]

When cutting, use your nail as a fixed point on the fused silica where you want to cut, approximate 2 cm from the end. Slide the ceramic wafer gently in one direction making an angle of proximate 45 degr. with the fused silica. Touch the end gently down and the column will break.

"wetting" the polyimide is very important and will sure help. My colleague, Jack Cochran uses the PressFits problemfree for MS -work and and even for vacuum MS connections (Restriction in front, 0.53mm into the MS) they work fine.

Despite it is possible to make these connections work, not everybody is succesful.

The MeltFit is a nice idea, though a little expensive. As far as I know activity issues have not been adressed. Also I have not seen any data with vacuum GC, which is the most challenging test for any connection.

[AICMM]

Mr. Krak,

The one thing I do (maybe a bit different than the other suggestions) is that I turn the gases off when I do my press-fits. I haven't used them for any MS work but I find that when I do dual column configuration that having the injector pressure off really helps getting that initial seal. Once well sealed I generally don't have problems although I like to use glue simply to prevent my gorilla hands from beating up the fitting too much.

Best regards,

AICMM

[chromatographer1]

Oh, YES by golly gosh.

The flow MUST be turned off. No pressure on the seal until it is installed and heated in the oven after drying.

Good point you caught there AICMM. Sorry I missed stating it, but I thought it was obvious.

Silly me.

Rod

[BZK]

Hi, I am using press-fit since 1985. No absolute solution I have found to tight "all the times" the connections.
All previous post correctly underline the good operation for the best connections.

From my point of view and in order of importance :

1- Perfect cut of column and is mandatory the use of magnifier to verify the correct cutting

2- No carrier must be present. If MS is connected and vacuum too some 5-10 psi must be used to avoid negative pressure into connection.

3-Heat to some 200-300°C the press-fit by iron solder or other device before column connection, push firmely the columns and, important, do not move by turning the connected columns

4- Not all press-fit/tight are equivalent. The best way is the use of target connectors instead of universal; the problem is that only one firm produce target connector, all other on the market are universal. From the point of view of universal connector the best connection are obtained with less conical device (more long) due to increase of ring connection. On the other hand, anyway, more long glass connections increase activity and this is not good.

5-Use of polymide glue surely help but only if the connection is well performed.

Roberto Barcarolo, Italy