Chromatography Forum

Greetings everyone,

I'm trying to repeat the latest version of European Pharmacopoeia analytical method (:1317), Ethanol (96%) / Volatile impurities (GC).

Link to previous version:
http://www.drugfuture.com/Pharmacopoeia ... /1317E.PDF

In newest method version only acetaldehyde + acetal calculation formula was changed:
[(10 x Ae)/(At - Ae)] + [(30 x Ce)/(Ct - Ce)] x (44.05/118.2)

For analysis I'm using DB-624 30m x 0.32 mm x 1.8 µm

As result I'm getting following areas of the peaks:
- 4-methylpentan-2-ol (Test s. B) - 157
- Methanol (Ref. s. A) - 35
- Acetaldehyde (Ref. s. B) - 2.6
- Methanol (Ref. s. B) - 1.8
- Acetal (Ref. s. C) - 9.1
- Benzene (Ref. s. D) - 1.2

In method is written that I supposed to used disregard limit that is "0.03 times the area of the peak corresponding to 4-methylpentan-2-ol (Test s. B)". So if I understood correctly disregard limit supposed to be 4.7.
So the first question is, do I need to apply calculated disregard limit to both Test solutions (A and B), or it's only for Test s. B?

The second question related to Acetaldehyde + Acetal calculation formula. In case in Test s. A Acetaldehyde or Acetal peak area is bigger then correcponding peak area it Ref. s., then calculation result will be negative.
How such cases supposed to be handle?

I checked all topics on the forum that related to this method, but unfortunately I can't find answers.

Thank you in advance,
Dmitrij

hi

The disregard limit applies to all chromatograms.
Ref B is needed to determine the value of the peak area of that limit.
So in your case, any peak smaller than 4.7 should be rejected; eg. doesn't count for Area%

mathematically you're right about the formula but it won't happen becauseone spikes the sample under investigation. So the peaks in reference solutions will always be larger than the ones in the unspiked test solution.
Otherwise something is very wrong and needs fixing (eg. injector maintenance)

Hello.

So the first question is, do I need to apply calculated disregard limit to both Test solutions (A and B), or it's only for Test s. B?

Usually disregard might be applied for all test solutions however this time imho it should be applied only for "other" impurities. Also "other" impurities are quantified via internal standard technique so only test solution (b) areas should be disregarded.

hi,

there is a simple and robust method for the direct determination of the quantitative content of volatile compounds in ethanol-containing solutions.

Practical usage of the method “Ethanol as Internal Standard” is presented here https://www.youtube.com/channel/UCXgL2c ... lW1oxOGqtQ .

For example, substitute the measured areas under the peaks of the investigated volatile components and ethanol in the corresponding cells on-line calculator http://inp.bsu.by/calculator/vcalc.html
and you will get the calculated values of volatile compounds concentrations.

Regards,
Siarhei

Thank you everyone for your answers.

Best regards,
Dmitrij

Greetings all,

Sorry for raising this topic again, but I really need some help with understanding mention European Pharmacopoeia method. Especially with limit calculation.

If I didn't messed up something, them standard substance concentration/areas of the peak in Referent solutions are following:
Reference s. A - Methanol - 0.2 µm/ml (ppm V/V) / 34.3
Reference s. B - Methanol - 0.01 µm/ml (ppm) / 1.8
Acetaldehyde - 0.01 µm/ml (ppm) / 1.8
Reference s. C - Acetal - 0.03 µm/ml (ppm) / 9.0
Reference s. D - Benzene - 0.002 µm/ml (ppm) / 1.2

But if will check Limits in the method, for example Methanol:
"not more than half the area of the corresponding
peak in the chromatogram obtained with reference
solution (a) (200 ppm V/V)"
so, basically if I understood it correctly the the max area of the Methanol peak that I can expect in Test s. A would be round 34? If pure max Methanol area could be half of the peak in Reference s. A (34 from pure Methanol + 34 from sample). I'm I right?
And I can't understand why it's written that max allowed concentration for Methanol is 200 ppm V/V, if peak area 34 is corresponding to Methanol concentration 0.2 ppm V/V.

The same thing relates also to Acetaldehyde+Acetal and Benzene limits. The max allowed area of the peak, is area of the peak from reference s. with corresponding to absolutely different concentration, not the one that is written in the limits.

P.S. I checked solution that you provided (Ethanol as IS), but unfortunately my boss is pushing me to use EP method

P.S. I'm really sorry if my question is stupid

Ref (a)
((100/1000)/50)*(5/50)*1000000=200 ppm
for methanol.
Ref (d)
((100/1000)/100)*((100/1000)/50)*1000000=2 ppm
for benzene.