Chromatography Forum

what is the best conditioning procedure for a varian ultimetal column, 15 m, .53 mm, with a 5% phenyl in dimethyl polysiloxane, for a column with a maximum operating temperature of 400 deg. C, and a maximum temperature for our method of 380 deg. C?

according to the manufacturer, they told me to condition at 385-390 deg. C for 4 hours.

however, the last column we had, which was a restek mxt-tg column, we were told to condition 1 hr at 400 deg. C. aside from manufacturer names, they were pretty much identical columns (same length, diameter, stat. phase) . the only difference was resteks' max. oper. temp. was 430 deg. C.

why the difference in conditioning times? i have always heard to condition either overnight or for 2 hours minimum. what is best? do i just do it for a couple of hours, hook it up to the detector, and keep going until the baseline goes down?

Capillary columns are pre-run by most manufacturers, who include a real chromatogram with the column. And there's much less total phase than in packed columns. And they're bonded phases. That said, if you still want to condition the new column, leave the detector end un-attached and most heat maybe 10 degrees above the maximum temperature at which you will use that column.

You should condition only as much as you need and no more.

Not a simple rule but a good one.

If you are going to use the column at a maximum temperature of 380°C then condition at that temperature for an hour. If that is not enough conditioning you will find out quickly. I suspect you need even less than one hour.

Why would you want to over-condition a column?

But at those temperatures make sure your carrier gas is pure and you have no leaks in your system. Oxygen will destroy a column quickly at those temperatures.

best wishes,

Rod

But at those temperatures make sure your carrier gas is pure and you have no leaks in your system. Oxygen will destroy a column quickly at those temperatures.

i realize this is probably the most noteworthy theme underlying capillary gas chromatography, as it seems to be on repeat. which indicates to me that this must be a fairly common problem for chromatographers...

am i doing enough by leak checking all the helium fittings, valves, OMI purifying tubes (oxygen/moisture traps), inlet, outlet, guard/column connections, all while heated and cooled? is it enough to assume that we don't have contamination in our helium lines as long as the traps are not yet spent (they change color when this happens)? if i'm not doing enough in this area, what are some more steps i can take to ensure an oxygen/moisture free column conditions?

thanks again for the support

em

Some biodiesel columns use a union to connect the 0.53mm ID retention gap to the 0.32mm ID analytical column. If this leaks, then the column can be destroyed in a few minutes.

It has happened to me.

best wishes,

Rod

Leaks hardly ever just appear unless a change is made to a system. Once all the plumbing upstream of the inlet is installed and leak checked it should be OK until you next change a gas purifier. Once a column is installed and the ferrules bedded in - run a couple of temperature cycles and re-check and tighten after each one - it can be expected to be OK.

Which leaves the inlet - especially the septum, which gets holes stabbed through it while it is exposed to high temperatures. This is by far the most likely place for a leak that can let oxygen into the system. The septum purge helps a bit - make sure that it is flowing, if your inlet operation allows it turn it up a bit. The best thing is to use very high quality dome tipped or side-hole needles and pre-drilled septa, be very careful about tightening the septum nut enough but not too much, and change the septum after every batch of samples, or once a day.

Peter