Detection Limit for methanol content using headspace GC

[Shalvin]

Hi guys

I am a MSc student and am confused about how to actually work out the detection limit...to get the signal to noise ratio value.

I am working on biodiesel.

I really need some help on this.

Shalvin

[Johnny Rod]

What is your question? The chromatography data system can calculate the signal:noise ratio (peak height divided by noise value) or you can work it out with a ruler if you are using a chart recorder. Inject a sample of known concentration, scale the peak down to a signal:noise of 3, this is your LOD concentration.

[chromatographer1]

There are two detection limits in play here.

One is the detection limit of the detector, calculated by the response of a known amount placed onto the column to the 'noise' of the detector, and

a second LOD which is how much can you detect by headspace recovery from the biodiesel sample using a certain set of parameters.

Both are determined experimentally with prepared standards of a range of concentrations to where no methanol is detected.

They are only calculated after collecting data and evaluating it. Most analysts prefer to assign a limit where the peak response is at least 3 times the amount of detector noise.

Best wishes,

Rod

[Shalvin]

Hi Rod

Thanks.

Yes, I am working in that line. Hopefully I can work it out.

Shalvin