Chromatography Forum

I am not sure what point you are trying to make - I see chromatograms where the internal standard and analyte peaks are similar in size, which is usually regarded as good practice. The problem with using ethanol as the internal standard in analysing trace components of beverages is that the ethanol peak is anything from 2 to 5 (or more) orders of magnitude bigger then the analyte peaks - with the undesirable consequences that have already been discussed.

Peter

Dear Peter,

let's discuss the taste of the proposed new method with those who have already tried it.
Till we are waiting for measured chromatograms from organisations took part in the interlaboratory exercise of “Whisky – Congeners CRM LGC5100”.
Practice is the judge in the last resort.

Best regards,
Siarhei

Recently we have received three chromatograms of the same certified reference material CRM LGC5100 Whisky – Congeners from three different laboratories.
The calculations were performed using the on-liner calculator here
http://www.inp.bsu.by/english/calculator_en.htm
or here http://www.inpnet.net/el/vcalc

Scan of Certificate and obtained results are presented in Table and in Figures 1 – 6.






Figure 1. Fragment of chromatogram of CRM LGC5100 Whisky – Congeners with following peaks:
1- methanol, 2 – ethanol, 3 – 1-propanol, 4 – isobutanol, 5 – 1-butanol, 6 – isoamilol
received from Claire.


Figure 2. Screenshot of the on-line calculated results from Claire.


Figure 3. Chromatograms of CRM LGC5100 Whisky – Congeners received from Dave.


Figure 4. Screenshot of the on-line calculated results from Dave.


Figure 5. Chromatograms of CRM LGC5100 Whisky – Congeners received from Ed.


Figure 6. Screenshot of the on-line calculated results from Ed.

Not bad.

Let’s emphasize that further validation of the proposed method can be performed on the basis of experimental data obtained in analytical laboratories during certification of material CRM LGC5100 Whisky - Congeners.
No additional materials or financial costs are not required for this validation.

In certification procedure of CRM LGC5100 Whisky – Congeners (Data of issue: November 2011) 16 profile authorities laboratories took part in the inter-laboratory study. They have measured chromatograms of standard working (calibration) solutions and chromatograms of CRM LGC5100 Whisky – Congeners. These experimental data may be calculated by the method of "Ethanol as Internal Standard" and by traditional method of Internal Standard, whereupon obtained results should be compared.

Best regards,
Siarhei Charapitsa

If relative bias around 10% is acceptable, then using ethanol as the internal standard works.

I note that Claire and Ed got all their biases in the same direction: positive for Clair, negative for Ed, and that Dave got all except the 1-butanol which has a very large uncertainty, negative. This biased bias is to be expected when there are problems with determining the peak area for the internal standard - in other words the ethanol peak is too large to be accurately measured, which has been my criticism all along.

Peter

There is an expanded version of the “On-line calculator” with the examples and description here http://inp.bsu.by/calculator/vcalc.html .

You should input only value of the areas under the peaks of the analyzed component and ethanol. Calculator immediately gives the concentration of the analyzed component in mg per liter of absolute alcohol (AA). Of cause, instead of predefined values RRF in the third column you can input for calculation your improved value RRF for your GC in the second column.
As an example, the results of determination of volatile compounds in the certified reference material CRM LGC5100 Whisky - Congeners are presented.
Comments and remarks are welcome.

Best Regards,
Siarhei

The YouTube channel was created in order to simplify the method validation procedure and subsequent implementation of the method in the practice of testing and research laboratories https://www.youtube.com/channel/UCXgL2c ... lW1oxOGqtQ .

Siarhei

Does it make me sound very old fashioned if I say that I prefer my methods to be disseminated and verified in the peer reviewed literature rather than on YouTube ?

Peter

The method "Ethanol is Internal Standard" for direct determination of volatile compounds in spirit drinks was proposed in the peer reviewed respected “Journal of Agricultural and Food Chemistry” ( DOI.org/10.1021/jf3044956 ). The possibility to use predetermined RRF was published here arXiv:1601.05587 .
The simplicity of the method and the high reliability of the experimental obtained data point to the inevitability of introducing the method into laboratory practice.
It's only a matter of time.
We decided to take advantage of the Youtube technology to acquaint the profile audience with the opportunity to validate the method directly in their laboratories without any additional material, financial or labor costs. The cost-free way of validation the method in the profile lab.
We are open to discuss the creation of a consortium to prepare and conduct international method performance studies of the method and subsequent procedure international agreed procedures with a view to its subsequent implementation in international regulations.

Siarhei