Hi Hafiz,

the %-Value is a combined value. The pure comparison results are the SI(Match) and the RSI(reverse Match) Value. A perfect reproduced spectrum will deliver values of 1000 for both.

The % value is combining the histogram depict above. Meaning if you have two perfect matches your % Value will only be 50%. Therefore you shouldn't focus too much on that value. Several good hits will deliver worse probalities. You should focus on the Match value. If the match value is above 700 and the spectra comparison is good, the retention index fit you are almost safe. A value smaller than 700 does not mean it is to be excluded, since there are many factors that can decrease spectra quality.

Use a low % value to check also hit nummer 2 or 3, but don't rely on that. One bad hit and no other hit will deliver a high %,.

Hope this was helpfull

Hello Hafiz,

i would strongly recommend to use retention time data as supporting information to identify your waxes, fatty acids or oils.

MS propability data is sometimes misleading especially for substances with alkylic chains. For example n-hexanoic acid and n-pentanoic acids have similar mass specs except for their molecular peak. And this molecular peak is relatively low.

N-hexanoic acid and n-pentanoic acids can easily distinguished by their retention times on the chromatographic systems. A more systematic approach is the use of Kovats indices (or more generally speaking retention indices). In practice You have to inject n-alkane mixtures in order to be able to calculate these indices. It works best for isothermal runs but it can be used also for temperature programmed runs.

Identification work will be strongly supported by GC retention data....

Thomas Stegemann

thanks for answer,

as you mentioned above that see the Match or R.match if above 700, then can use that ,

but you can see in the image that almost all the compounds showing above 700, so will i have to use all that compounds and than identify ? or only need to 1st ?

or how many i should use ?

Ludwig Gruber

Thanks for Answer,

Dear sir as you recommended to use of retention time data as supporting information to identify waxes, fatty acids or oils.

but in image file you can see that there are many others compunds with the similer Retention time data, so what should do in that case?

should only select the top one?

or how do selection?

Hello Hafiz,

there seems to be a misinterpretation of the "R.match" value. The R match is not the "Retention time match", it is "Reverse match" which is a mass spectrometric parameter that is something completely different to RI data.

One example for the use of RI data: NIST tells You that Your substance is n-hexadecanoic acid. You can verify this by a look in the NIST library. You can find a value of 1961 for the Kovats' RI (non-polar column with temperature ramp). If you have used also a non-polar column like the DB-1 with temperature ramp you can inject the n-alkanes C19 (RI=1900) and C20 (RI=2000). They should elute shortly before (C19) and after (C20) your compound. This is the verification step i already mentioned. This step can also automated by software packages of some vendors, but this is another story.