Chromatography Forum

Hello, I am having trouble getting nice peaks for some very hydrophobic compounds. Not sure if there is some obvious explanation that always lead to these types of peaks?!

My setup is as follows:

Varian CP-3800 GC
Varian VF-1701ms column (30 m, 14% cyanopropyl/phenyl, 86% PDMS)
Detector is Saturn 2000 MS

Method is as follows:
Silyl derivatization with BSTFA
Injector T: 280C
Temp program:
100C, hold 2 min;
ramp to 280C 40C/min, hold 12.25 min;
note: I did a slower ramp and got the same result.

I have been trying to run standards and have gotten good resolution on the more polar compounds that elute first, but the less polar are too broad on the tail end which will make identification in a more messy actual sample troublesome.

Also my compounds are all aliphatic primary alcohols with 16, 20, 26, and 28 carbons (waxes when pure at room temp)

Here's links to pictures of sample chromatograms.

https://drive.google.com/file/d/0B_uR58 ... sp=sharing
https://drive.google.com/file/d/0B_uR58 ... sp=sharing

Thanks very much!!

Toby

Why bother to derivatize ?, those long-chain alcohols will chromatograph just fine if you have a reasonably inert system. By derivatizing you make already large molecules even heavier, and more difficult to get out of the inlet as a sharp band.

A clean inlet liner cannot do any harm, increasing the inlet temperature might help, ramping at a less drastic rate will elute all the peaks while the column temperature is rising which will sharpen the later ones. Molecules as big as your derivatives might also be sticking in the MS - increase the trap temp if you can.

Peter

tmaxwell,

You might be overloading your phase. Are you running splitless or split? How thick is your phase, what concentration are you running, and what column id?

Also, as Peter notes, you might have a cold spot. Especially in the transfer line or MS.

Best regards,

AICMM