FAMEs

[bm4292]

i have a HP-88 100x25x0.2 column in a HP5890 FID S/S system. I have set up a program: 50C (5min) to 200C@10C/min, hold 10 min, then 4C/min to 240. 225C inj, 250Cdet. H2 @40cm/sec, split ratio ~100:1. Straight, empty 4mm liner. Problem is, the short chain FAMEs (C4-C10) are not giving much response in my standard, compared to literature traces. This also happens when I was running @30cm/sec, and also starting at higher temp (up to 180C). Any ideas? TIA

[HW Mueller]

Discrimination in splitting?

[chromatographer1]

Another possibility is that the sample vial you are using is losing the more volatile FAMEs due to the temperature environment in which it sits. It may not be sealed tightly, or the sample may have lost the volatiles before the sample was put into the vial, or syringe needle if you are not using an autosampler.

[Rick]

Hello!

I think that your injector temp is to low, try 250c

So,why do you maintain initial temperature to 50 for 5min???
1 min is habitually o.k.

Put a small piece of glass wool in the center of your liner

Good luck!

Sorry for my english...i'm a french canadian!

[Rick]

Hello again!

What is your column lenght in your injector???for my FAME analysis, i use 3.5cm.

Bye!

[bm4292]

Wow! Didn't expect such a response coming into work this morning. . . I also suspect some kind of discrimination, just wasn't sure what to try. Agilent helpline suggested putting the column 6mm proud of the ferrule in the inlet instead of 2mm, which gave me 1/10 the peak size overall, but same problem. Will try 250C injector and 1min @ 50C today. Also, have got a wool plugged liner on order, but may try a self-fix before it arrives (bit of a newbie). The problem was exactly the same when I simply cracked open the (frozen) ampoule, transferred to the supplied amber vial, and injected.

[Rick]

Hello again!
FAME on freezer.....are you sure that you don't have solid (precipitate)in your cold standard????I think C4 to C10 "freeze" at this temperature.
Transfer your standard in your vial when your std is at room temperature.

[HW Mueller]

Reducing the splitting ratio might be the easiest way to find out where the fault lies.

[bm4292]

Rick, you may be on to something! I will take extra care with tthe next ampoule.

"je me souviens"

[chromatographer1]

of course you could inject a small amount (wet needle or 0.1µL with an air gap)SPLITLESS and see what you see.

[DR]

Ask the author waht kind of head pressure corresponded to that flow setting - your flow may not be as accurate as you think.

[bm4292]

thank you for these suggestions also. I tried a 50:1 split, with equivalent results just now. Head pressure is 254 kPa@100C, but I was running before at a nominal 30cm/sec (187kPa@100C), with the same issue. Should I go faster than 40cm/sec?

[bm4292]

The winning solution was: using a glass wool plug in the inlet liner. Thanks to all who participated