Chromatography Forum

Good afternoon,
I'm working in an environmental lab that analyzes waste streams for VOCs on an Agilent GCMS (7890A and 5975C, respectively). I've been doing some maintenance that doesn't appear to have been done as often or as recently as it should have, as well as had the AC board replaced last week due to repeatedly blown primary fuses.
While the GCMS was down prior to the service call, I figured it was as good an opportunity as any to change the column for what was labelled as an unused, appropriately stored column. Once everything was running again, however, it became abundantly clear that this column is not only used, but based on the severely noisy baseline and the column bleed, it was not taken care of very well.
So I am accutely aware that the only true solution is a new/maintained column, which I will be installing as soon as my ferrules arrive.

Now, my question to you all, is there any possible way I could squeeze whatever life is left out of this column while waiting for the ferrules? I baked it out once and am baking it out again, but it does almost nothing to subdue the rising baseline. Would solvent rinsing help ease the bleed or is this column DOA?

Thanks for your time, this was my first topic on this forum, but I've been reading along for a while now.
Alyssa

Several times I backflushed bonded capillary columns with solvent such as methylene chloride, helped. We had purchased a little apparatus to do this, and then dried out the methylene chloride with helium.

I always stocked spare/extra stuff like ferrules around...shaking head right now.....

This month was the first time I've seen of, heard about, or used ferrules, but thanks for the helpful suggestion!

What is the column specifications? Brand, phase, diameter, film thickness? Different columns have different bleed characteristics so if we know more we may be able to suggest if it is good or not.

How will you be doing VOA analysis? Purge and trap, Headspace, other?

Many times for VOA you don't need to go to max temperature to have all the analytes elute so maybe you can get results before the bleed takes over.

I'm home right now, so don't know max temps off-hand, but they're in the 30p-350 range and it is. Restek RXi fused silica 60m column (0.32mm, 1.8um).

We run headspace with a 16 minute run time and, I believe, with a ramped temp maxing out around 225 or 250. The bleed tends to interfere with PCE at about 9 5 minutes. Bleed begins to become apparent at 8 minutes when m/z 207 starts bumping up and rises.

What is the carrier flow rate into the MS?

A 0.32 column is not going to perform well at the 2ml/min or less that should be going into the MS. If the flow is down at 1-1.5 ml/min where most run MS flows then it could be causing some of the extra bleed.

If the column ever had oxygen get into it while at elevated temperatures it can start to bleed and not much way to fix that without replacement.

For volatiles analysis I run a 40m 0.18mm 1um Rtx 502 or Rxi 624MS, depending on what I need to separate(acetonitrile will co-elute with an interfering peak on the 624). I also like the 60m 0.25mm 1.4um columns of the same phases.

The only other option is to take it up to maximum isothermal temp overnight and see if that cooks off the bleeding stationary phase and lets you have good baseline to the lower max temp you are running normally.