%area normalisation

Discussions about GC and other "gas phase" separation techniques.

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Hi there,

Currently I am doing something about the GC solvent testing. It is the assay of acetone (IPA is the specified impurity). The method indicates to prepare a 0.2%v/v IPA in acetone, then report the acetone result as % area normalization , and report IPA as % v/v. I just wonder who can clarify with me what is the different between %area normalization and %v/v, and % area

Thank you very much!

In reverse order:

% area is the percentage of the total peak area on the chromatogram made up by the peak for the analyte. e.g. if you have a peak of area 5000, another one of 4000 and your analyte peak is 1000 the % area for the analyte is 10%

% v/v is the percentage of the volume of a liquid made up by the analyte e.g. if you have 10 ml of ethanol in 1 l of wine it has 10 % ethanol v/v (and weak wine !!)

% area normalization - I have never heard this one, best to ask whoever wrote the procedure.

Peter
Peter Apps

Just to add to Peter's reply - as an example of what I understand by % area normalisation is in a chromatogram of fatty acid methyl esters. The fatty acid ester peaks add up to,say, 90% of the total area. You may only want to report the ratios of the relevant chainlengths, the other peaks being lots of minor impurities. The 90% is recalculated by multiplying the % of each peak by 100/90 to make them add up to 100%.

Strickly speaking area % normalisation should state what you are normalising it to i.e. in this case normalised to 100%.

Regards,

Ralph

Peter wrote

if you have 10 ml of ethanol in 1 l of wine it has 10 % ethanol v/v (and weak wine !!)


weak wine in deed! 10 ml in 1 liter (1000 ml) is only 1% v/v.

Sorry Peter, just happened to notice this and couldn't let it go.
Regards,

JZT

Thanks JZT - just checking to see who was paying attention !! :oops:
Peter Apps
Hi thanks guys!

Give more details. Currently I am checking the IPA in Acetone. the SOP say report the IPA and acetone in % area normalization. And the standard contains 0.2%v/v IPA in acetone is prepared and injected. Agilent Chemistation is used to calculate. Since it is %norm, therefore, the quantitation, we select %norm in Chemstation and will follow it to calculate the response factor and then use this response factor to calculate the content in sample.

So in this case,
1. if there is no IPA, then acetone will be always 100% percent no matter how many unknown impurities there is.
2. Since the standard is in %v/v, the sample content should be in %v/v or % area norm?

Really confused! Thank you very much for the clarification!

I honestly think that you need to check in-house with whoever understands this procedure, because as you present it, it does not make a lot of sense.

If the standard has 0.2 % IPA, presumably the samples do as well, so the acetone is 99.8 % if there are no other impurities. Unless you do multiple injections and take means, a GC split injection is not repeatable enough to distinguish between 99.8 % and 100 %. Therefore, the area of the acetone peak cannot be used directly to determine acetone concentration.

If the response factor corrects for the difference in response of the FID to the two different substances, then with a single standard you can just as well take the IPA: acetone peak area ratio for the sample, divide it by the ratio for the standard and multiply by 0.2% to get the IPA concentration in the same units as in the standard (V/V).

You could take acetone concentration as 100% - IPA%, but as you have noticed this will only work if there are no other impurities. A major problem with 100% - IPA is that the FID does not detect water, which there is a good chance that the acetone contains.

Peter
Peter Apps
In my experience Area% is strictly based on the Areas of the Chromatogram i.e. no calibration and no response factors are involved. Therefore the responses of all peaks are assumed equal.

Therefore Area% is kind of a crude way to calculate your results.

JW
Applied Instruments

Area % methods can be fine if you are looking for the disappearance of a compound during a reaction or if you want to check the ratio of compounds against a standard ratio. I have set up area % methods with correction factors to take RRFs into account. It all depends on what is set as the pass fail criteria.

GCguy
GCguy
In chromatographic calculations, % area normalization ususally implies that the individual response factors (amount/area) for each compound (including those for the unknowns) are to be included, which can be pre-determined either from gravimetrically- or volumetrically-determined standards (w/w or v/v, respectively). If you are using an FID, you can apply ECN-based response factors. In contrast, % area assumes that the same response factor (by default 1) are used for all compounds and is good mostly for qualitative purposes.

In Chemstation, while generating a Calibration Table one can choose the reporting unit (%v/v or Vol% or anything else) in Calibration Setting line and must specify the mode of calibration (%area, % area normalization, ESTD% or ISTD%) in the Report section. The final report will be in the unit you chose in the Calibration Setting taking into account the mode of calibration you chose in the Specify Report section.
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