Loss of triglyceride sensitivity

Chromatography Forum: GC Archives: Loss of triglyceride sensitivity
Top of pagePrevious messageNext messageBottom of pageLink to this message  By mtarrien on Friday, July 9, 2004 - 09:11 am:


I have an HP6890 with .5m guard column and 15m DB-5HT column which I use to test glyceride and methanol content in methyl esters (biodiesel) samples. My triglyceride recovery rate dropped down to ~20% so I did the usual PM (changed septa, trimmed column and installed new ferrules, replaced trap) at which time I saw an increase in noise and spiking and still low recovery rates for tri's. I switched from front FID to rear but this made no difference either. I then had an Agilent Service Tech come out and we were able to eliminate the noise (which he believed to be caused by some tiny graphite particles which collected inside the jet) but still poor triglyceride recovery. We called the Agilent Service Tech out again and he did some more PM on the machine but now we have no triglyceride recovery at all. I've replaced precolumns and tried two new columns (after conditioning) and we still see no triglyceride peaks using good, known standards. I then shot a Soybean Oil sample which I siylated but the triglyceride peak is small and is shaped like a mound with a starting RT of around 23 minutes and ending at 26 minutes. Here are temperature programming we use:

Pressure: 6.1 psi
Flow: 2.3 ml/Min

50C initial for 1 min
15C/Min to 180C and hold for 1 min
7C/Min to 230C and hold for 1 min
45C/Min to 370C and hold for 10 mins

I should also mention that of the six components in the standard sample I run-all have 95-100% recovery except for triglyceride. Any suggestions/ideas to try and resolve this issue would be greatly appreciated...

Top of pagePrevious messageNext messageBottom of pageLink to this message  By mtarrien on Thursday, July 15, 2004 - 11:28 am:

Problem solved!

For anyone who may read this post with the same problem-the only thing we can figure is that the inside of the jet became contaminated with graphite. Under examination of a microscope-the inside bore of the jet appears free of any debris so we believed them to be good. We had tried changing jets but unfortunately all of them were contaminated (including two new ones we installed) by graphite from the ferrules. Since we operate our GC at high temps we are forced to use all graphite ferrules and while installing them we most likely overtightened them and this caused some graphite to accumulate in the jet...

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