Chromatography Forum

Hi
do you work at high senitivity?(analysis at the ppb range)

Hi, I work with 2 GC-14 B, sometimes at higher sensitivity. Please tell me what do you want to know

Regards

DL

I work with GC shimadzu 14A (FID) equipped with split/splitless injector.
column is PEG.
I inject manually with 1ul syringe.((FAME) methyloleate), split ratio 1:50.
bu the results do not repeatible, and can not detect low concentration (below 1 ppm).
injector lines and detector are clean.
my column is new and conditioned.
carrier gas is helium.
please help me
have you the same problem?
thank you.

Your injector or detector temperature maybe too low.

Your column temperature may not focus your injection plug properly.

Your injection technique may not be suitable.

Your detector may have the wrong flows. Check with a known std for sensitivity of the detector.

Your actual split ratio may not be what you think it is.

good luck.

Your injector or detector temperature maybe too low.

Your column temperature may not focus your injection plug properly.

Your injection technique may not be suitable.

Your detector may have the wrong flows. Check with a known std for sensitivity of the detector.

Your actual split ratio may not be what you think it is.

good luck.

hello
injector temp: 230
detect temp:240
column temp:150C-5C/min-220
I check the flows, these are correct.
if sensitivity to be low,do I do?
thanks

Hi again, you must detect your sample at 1 ppm. I suppose you're using the 10^3 range, and working with a FID. Are the H2 and air flows in the optimum range?
Anyway, your can work with a low split ratio, i.e. 1:10.
BTW what is your sample's solvent?

good luck

MB

Hi again, you must detect your sample at 1 ppm. I suppose you're using the 10^3 range, and working with a FID. Are the H2 and air flows in the optimum range?
Anyway, your can work with a low split ratio, i.e. 1:10.
BTW what is your sample's solvent?

good luck

MB

thanks for reply
I work at 10^1 range, and FID.the concentration is 25 ppm but the peak is very small.
sample solvent is methanol.
I use standard addition for quantitation of FAME(oleic acid), is it correct?
and my resalts aren't repeatable.
best regards

Did you check your detector sensitivity with a hydrocarbon std?

You must determine if the GC detector is working properly.

If it is then you must suspect your std.

If it is not, then you must repair the problem.

Good luck.

Hi, If your sample is oil and you do esterification to metylesters, you may have problem in your esterification technique, may not have two layers well seperated (add saturated NaCl solutin to make good separation) or incomplete esterification (use less amount of sample).