Chromatography Forum

Hello all; have a problem and am wondering if anyone has any ideas......operating an agilent 5975C-7890A and am experiencing what would seem to be a large leak....cannot pump down and am continuously getting foreline pressure too high....recently (within the last month) we had a service visit where basically every part of the system was serviced and ok'd....since then we have need to change capillary tubing and this is when the problem arose. I have isolated the ms by closing off the interface to the gc which results in the ms being able to pump down....as soon as I reattach the line into the the gc, pressure problems come up again. I've leak checked the gc and have tightened fittings in the inlet, changed the septum...still experience pressure problems.....anyone have any advice?

Welcome to the forum.

A leak big enough to compromise pump down has to be on the MS itself - so do not worry about the GC. When you say that you closed off the interface to the GC did you take out the column and replace the column nut with a seal, or did you remove the transfer line and blank off the hole where it attaches to the MS ?

What column are you using - length and diameter, and what were the dimensions of the column that you removed ?

Peter

your problem is in column connection to transfer line. work on there.

Welcome to the forum.

A leak big enough to compromise pump down has to be on the MS itself - so do not worry about the GC. When you say that you closed off the interface to the GC did you take out the column and replace the column nut with a seal, or did you remove the transfer line and blank off the hole where it attaches to the MS ?

What column are you using - length and diameter, and what were the dimensions of the column that you removed ?

Peter

I closed off the interface to the GC by removing the column and replacing it with a seal cap to the threaded end in the GC.....the fact that the MS can achieve pump down with being sealed leads me to believe the problem is in the connection on the GC side into the interface; I don't disagree because I don't know....but what leads you to believe the problem is still in the MS?

your problem is in column connection to transfer line. work on there.

column connection to the transfer line......gc side?

your problem is in column connection to transfer line. work on there.

column connection to the transfer line......gc side?

yes, the nut that fixes column to transfer line. you assume that it's tight enough but usually it's source of leak. tighten it more and more till you get raid of leak. don't forget to use vespel ferrols there.

Welcome to the forum.

A leak big enough to compromise pump down has to be on the MS itself - so do not worry about the GC. When you say that you closed off the interface to the GC did you take out the column and replace the column nut with a seal, or did you remove the transfer line and blank off the hole where it attaches to the MS ?

What column are you using - length and diameter, and what were the dimensions of the column that you removed ?

Peter

I closed off the interface to the GC by removing the column and replacing it with a seal cap to the threaded end in the GC.....the fact that the MS can achieve pump down with being sealed leads me to believe the problem is in the connection on the GC side into the interface; I don't disagree because I don't know....but what leads you to believe the problem is still in the MS?

The transfer line is part of the MS, and you have almost isolated the problem to the connection of the column to the transfer line. Almost, but not quite, that is why I asked about column dimensions - which you have not answered - a short or wide-bore column properly connected could create the problem that you describe.

Peter

Welcome to the forum.

A leak big enough to compromise pump down has to be on the MS itself - so do not worry about the GC. When you say that you closed off the interface to the GC did you take out the column and replace the column nut with a seal, or did you remove the transfer line and blank off the hole where it attaches to the MS ?

What column are you using - length and diameter, and what were the dimensions of the column that you removed ?

Peter

I closed off the interface to the GC by removing the column and replacing it with a seal cap to the threaded end in the GC.....the fact that the MS can achieve pump down with being sealed leads me to believe the problem is in the connection on the GC side into the interface; I don't disagree because I don't know....but what leads you to believe the problem is still in the MS?

The transfer line is part of the MS, and you have almost isolated the problem to the connection of the column to the transfer line. Almost, but not quite, that is why I asked about column dimensions - which you have not answered - a short or wide-bore column properly connected could create the problem that you describe.

Peter

The column we are using is a DB Petro 100mX.25mmX.5um......at this point I have the MS isolated and pumped down allowing me to run an air/water tune, and in relation to 69; 18 28 and 32 all look ok......I'm wondering if the ferrule to the interface could be the problem.

OK, the column itself is not the problem (unless it is broken close to the downstream end - do a visual check). Remove the exsisting ferrule and nut and start again with a new ferrule. Follow the manufacturer's instructions for column installation. Do not just keep cranking the nut tighter and tighter - you will sooner or later crack the ferrule and drive particles down the transfer line.

Peter

Another problem with continued tightening on a 5975 is you can actually twist off the threaded end of the interface( know this from experience).

Things to check would be the size of the ferrule, for the 0.25 column you should be using a ferrule with a 0.4mm hole, any larger and you will have difficulty with it sealing. Another trick is to bake your ferrules in the oven for a few days at 250-300C to preshrink them so they seal better.

If you tighten the fitting until you can no longer move the column by pulling on it then it should be tight enough to initiate a pump down, but can still leak and you will have to tighten it in small increments of about 1/4 turn until it is completely leak free. Also be sure that the tapered end of the ferrule is into the nut not into the interface, it seems backwards but it is how it is designed.

Just a quick update; we changed out the column and made some interior changes....still had a leak at the ms chamber O-ring but have since been able to get it seated. Air, water, nitrogen all look low and good now. Thanks everyone for the help!

Thanks for the feedback.

Peter