Quantitation Mode

[karthic]

Hello everybody

As I am fairly new to this world of analytical chemistry I am unable to understand what quantitation mode should I use for quantification.
I have the following options:
ESTD
ESTD%
Norm%
percent
ISTD
ISTD%
I presume that percent basis need no calibration table and that is teh worst mthod of analyzing data.

I have calibration table for all the compounds I need. So, I am curently using the ESTD method.

Also, we cannot use the ISTD/ISTD% as i m not using any internal standard.

I am using gas samples for analysis and I want my data in percentage. Currently, what I do is that I get my report in g/l and I do the manual calculations for converting them into %.
When I use ESTD%, I get a different report than I manually calculate.

Also, I want the sum of all data as 100% which I miss by 2-5 % while calculating manually. I get all unusual answers while I use the normalization techniques.

Please give me insights on how these calculations work and which shoudl be the best for me.

Thanks.
Karthic

[larkl]

Correct, the percent is just the ratios of all the areas. Since this doesn't correct for different detector response for different analytes, it's not that great. If you want your totals to add up to 100%, you would use norm%. It will use the response factors from the calibration to adjust all the areas (not exactly, but hopefully you get the drift) then it'll ratio them so all add up to 100. You can just run your calibration gas and calibrate. This'll set your detector response for each component. Then set up a norm% report and you should be good to go.

I've only seen norm% used for FID runs, not so much for other (TCD, PDHID).

Understand that you aren't correcting for non-detected components. For example, you run the sample using FID detection and norm% it to 100%. What if the sample contains 20% hydrogen? If you knew this, you'd then adjust the 100% down to 80. If you don't know that the sample contains other non-detected components, your results are biased.

[karthic]

Thanks Larkl
The piece of information u gave is really helpful...

But How about using a ESTD% for getting the percent values. It should calculate based on the external standard and give results in percentages. Right?

It gives me a different report when i use that.

Karthic

[Ron]

ESTD% should correct for the variations in detector response for the compounds, so this should be a more accurate percentage than using percentage. There will be more of a difference with a TCD than with an FID in most cases.

[larkl]

You can use the ESTD%, but the totals may not add up to 100. IF you use the norm%, it's the same as the ESTD%, but the total always adds up to 100.

[mbicking]

The ESTD% and ISTD% selections use the "Sample Amount" value in calculations. The formula is:

ESTD% = 100*(Amount Found/Sample Amount)

The most common application would be in recovery studies or a formulation analysis, where you want to know the % composition of an active ingredient.

I don't think that this approach will produce the kind of information that you want.