External calibration varian GC 3800

avatar: Chemist_
Chemist_
2 posts
Replied to Chemist_'s post on September 19th, 2012

Hi,

I'm a beginner on using GC.

I want to know how to define peaks for the calibration standard.

plz help me

avatar: Sarah T
Sarah T
58 posts
Replied to Chemist_'s post on September 20th, 2012

Hi,

Can you tell me what compounds you are calibrating for and what your GC conditions are?

avatar: Chemist_
Chemist_
2 posts
Replied to Sarah T's post on September 22nd, 2012

Hi

I'm calibrating for total petroleum hydrocarbon C6 to C 28

And about my conditions; I'm not sure if you mean these:

Injector temp 250 C

Splitless

*Flow/pressure

Pressure(psi)_Rate(psi/min)_hold(min)

1_ _2.3

5 _ 0.5_23.87

*Column oven

Temp(C)_Rate(C/min)_hold(min)

45_ _ 3.00

275_ 12.0 _ 12.00

* Detector

FID

Temp 290 C

The peaks are shown in the chromatogram but the retention time is not shown for all of them.

Also when I click on "view results only", those peaks were not mention in the report

avatar: Sarah T
Sarah T
58 posts
Replied to Chemist_'s post on September 23rd, 2012

Hi

If you have not set up a method specifically for this analysis you need to do so and use this every time you run samples. In this you need to input the retention times for the peaks you want to look at.

If you go through a chromatogram you already have and manually obtain retention times for peaks not assigned currently and put these in alongside the assigned peaks; your software should then pick up the peaks. Also remove any peaks you don't want!

Also you need to define a peak window for each peak because peaks are not vertical lines at the specified retention time and have a spread before and after. The peak window should be set to reflect the shape of the peak i.e. a wider peak window for a broad peak so that the software picks up when it starts and finishes. If your peak window is too narrow the software will not find the peaks.