Chromatography Forum

Dear everybody

This chromatogram is from a new 5975B Agilent MSD


what you are think the resaons for this?
the column is HP-5ms (30m & 0.25mm)

Dear Che313,

You should give more information about the method if you expect good response!
Be more specific about oven temperature program, injector and detector parameters, carrier gas parameters, type of analytes involved, what are you trying to achieve etc.

Regards

Sample too concentrated? dirty inlet?

Dear Che313,

You should give more information about the method if you expect good response!
Be more specific about oven temperature program, injector and detector parameters, carrier gas parameters, type of analytes involved, what are you trying to achieve etc.

Regards

oven:
initial 200 C
then 25 C/min to 280 C hold 4.8 min
inlet 250 C
MS Quad: 150 C
MS Source: 230 C
carier: He 1.0 ml/min
target: d9-thc (tetrahydrocannabinoid)
dervetise: MSTFA

Sample too concentrated? dirty inlet?

it could be
which chemical I have to run to insure my GC is functuned properlly?

Che313,

What column are you using, what solvent are you using? Are you running SIM or scanning? If scanning, can you post a spectrum, if SIM what ions? How does your tune look? Still need more data.

This could very easily just be junk from your sample but it is hard to say without more information. Your MS came with a test mix (typically octafluoronaphthalene since it has a great EC capture coefficient) so try running that under the recommended conditions and see what that looks like.

Best regards.

Che313,

What column are you using, what solvent are you using? Are you running SIM or scanning? If scanning, can you post a spectrum, if SIM what ions? How does your tune look? Still need more data.

This could very easily just be junk from your sample but it is hard to say without more information. Your MS came with a test mix (typically octafluoronaphthalene since it has a great EC capture coefficient) so try running that under the recommended conditions and see what that looks like.

Best regards.

thank you for your attention
the coulmn as mensioned is HP-5ms
solvent is ethyl acetate
scan mode
tuning is good - same as supplied with ms

we didn't got the test mix!!
is ethyl acetate good solvent for blank and for syring cleaning purposes?
do you suggest another kind of solvents for syring wash? ( now we use ethyl acetate pre and post injection 2 times)

Looks like a GC issue, not an MS issue. Why not start with something really simple, like methyl laurate or dodecane dissolved in solvent? Anthing you have that's relatively pure, non-polar and maybe 150 to 350 molecular weight......

Che313,

You said that you're analysing THC derivate. Did you extract it from biological samples? If yes, are you sure that sample preparation method was suitable? Maybe you have interfering compounds from your sample.

You said also that you used derivation of your target compound. Are you sure that the derivation reagent is pure enough? Derivation is additional step where you may contaminate the samples.

Did you run blank to see whether your solvent is free of contaminations?

Regards

Che313,

You said that you're analysing THC derivate. Did you extract it from biological samples? If yes, are you sure that sample preparation method was suitable? Maybe you have interfering compounds from your sample.

You said also that you used derivation of your target compound. Are you sure that the derivation reagent is pure enough? Derivation is additional step where you may contaminate the samples.

Did you run blank to see whether your solvent is free of contaminations?

Regards

yes its extracted from urine. although the prepration method has a refernce, it can't be said it will be clear 100% from interfering. And also I can't garntee the dervative is clean 100%.

If those reasones are affecting I will be satisfy, because I was thought the problem from GC or MS it self. for that I was asking about a reference material I have to run to check the functionality of my GC.

When you say you are derivatizing, do you mean making trimethylsilyl (TMS) derivatives? If so, do several of the peaks shown have significant 73 m/z ion? If not, you may not have enough derivatizing agent in there to react with remaining water and have excess to react with your THC. Maybe try more derivatizing agent.