column bleed

[ece]

I work for a facility that is using a GC to analyze biodiesel for partially reacted and free glyceride content. We have made three sets of all the calibration standards and are analyzing those.

My concern is for what looks to be stationary phase eluting or what I suppose is called column bleed at the termination of the run (380 C according to the ASTM method 6584, held for ten minutes). The column we have is a j&w db-5, part number 123-5711, which my boss has informed me has a max of 350 C. When we purchased it, we were informed that nobody makes a column higher than 350 C.

Although I understand columns will inevitably bleed no matter what temp. they are designed for, I am concerned about the useful life of our column (they are, after all, easily over $300 each).

My questions are:

1) for bd analysis, what kind of life can we expect on a column designed for 350 deg. C, but for which we have to max out our method at 380 deg. C?

2) for bd chromatographers, what kind of column do you use?

3) does the length of the guard column (ours is 5m) have any impact on the life of a column at high temperatures? should we get a longer guard column?

4) should we reduce the holding time for the final temperature ramp (i.e. 380 deg. C at, say 5 minutes instead of 10 minutes)?

5) since we will be primarily using yellow grease, which has a lower carbon count than our triolein standard does, could we get away with lowering the final temperature to, say, 345 deg C?




Thanks

[chromatographer1]

Three recommendations of columns you might like:

(I don't work for any of the three)

Varian Select Biodiesel ( a metal 5% phenyl column ) very low bleed at 380°C

Restek Mtx-500 ( a metal carborane column ) VERY VERY low bleed at 380°C

SGE HT-5 w/ guard (P/N 054640) a polyimide coated column but very low bleed at 380°C and the coating held up very well under temperature, unlike many other, quite a surprise !

I have heard customers praise these columns.

That is not to say there are not others out there which also do well.

Your other questions I will allow someone else to address.

best wishes,

Rod

[Consumer Products Guy]

I like Ultra Alloy* stainless steel high temperature bonded methyl silicone capillary column 10 m x 0.25 mm x 0.15*m film thickness (Quadrex #UAC-1HT-10-0.15F, telephone 1-800-275-7033), fine over 400 C.

[jf]

chrom1,

thanks for the advice. I work with ece and posted some stuff the other day here

I looked up restek's mxt-500 series column
http://www.restek.com/restek/templates/ ... &ig_id=599

it is a different diameter than what we are using now, and only 6m long. Would this work for the D6584 method?

thanks!

[Bruce Hamilton]

Sometimes, very rarely, bosses can be wrong. According to my Agilent catalogue, and the Agilent website, that column has a maximum allowable operating temperature of 400C. Ask agilent whether that's the column they use in their Biodiesel analyser. If not. ask what they use.

Given that it was intended for triglyceride analysis ( which will be the last peaks on your chromatograms ), it's quite likely to last a long time, and I'd use it till it dies.

Basically, if you are analysing in accordance to the standard, then set up and follow the method.. It's been around a while ( as the European method ), and I've used ordinary SGE columns ( not the high temp version ) for acetylated MAGs/DAGs/TAGs for up to 6 months continuously without issue.

The problem is not breakdown of the internal stationary phase, but the decomposition of polyimide coating, which becomes brittle, and you have to take extra care to ensure the column doesn't break from physical stress.

Reducing temperatures etc may result in junk appaearing on the next chromatogram. Follow the method, use the column you have, and consider replacing it with one of the ones suggested by Rod above if it doesn't perform.

Please keep having fun,

Bruce Hamilton

[Peter Apps]

Running at these temperatures you need to make sure that your carrier gas is as free of oxygen and water as is humanly possible.

Peter

[ece]

Thank you for your comments.

<Running at these temperatures you need to make sure that your carrier gas is as free of oxygen and water as is humanly possible.>

yes, thank you, we have an oxygen/moisture trap on our carrier gas line and we live in an incredibly dry climate, so i don't think that will be an issue for us.

<The problem is not breakdown of the internal stationary phase, but the decomposition of polyimide coating, which becomes brittle, and you have to take extra care to ensure the column doesn't break from physical stress.

i see, thank you. we will probably use a more robust column for temperature in the future, but we will continue to use the one we have for the remainder of it's useful life.

which brings me to my next question: clues to knowing when your column is "dead"?

thanks

[Bruce Hamilton]

...which brings me to my next question: clues to knowing when your column is "dead"?

Generally, as columns are used at high temperature, the retention times slowly decrease, until you can no longer resolve critical peaks.
You will notice the high temperature bleed also slowly decreases from week to week.

If the column is being subjected to junk, or is not being kept oxygen and moisture free, analyte peaks will start to tail and merge together. The first option is replace the guard column, and then to cut the front 0.2 - 0.5 metre off the column, but my experience has been that the column is usually almost dead ( hospice time ), and a new one should be ordered.

Because of the high operational temperatures, there's seldon a need to condition these columns, just to ensure carrier is flowing when ever the column is at above ambient temperatures.

If junk has accumulated in the injector, then sample peaks may disappear whenever you restart, especially the MAG and DAG derivatives. The tailing may not be pronouced, but you will see the derivative peaks increase with each injection. You need to keep injecting standard mix until consistent results are obtained, but it may be time to replace the liner..

If the high temperature bleed becomes excessive over months, your column is asking for the Last Rites. You should investigate sample preparation to understand why high MW junk is appearing

In my experience, for MAGs/DAGsTAGs analysis, the column usually dies because the coating becomes brittle and the column breaks,. If you are having to replace columns more than one every 3 - 6 months, you should be looking at your carrier gas purifiers and start up routines.

Please keep having fun,

Bruce Hamilton