Mr. Wau,
Mass spectrometry provides far more comprehensive information about the analytes, such as absolute quantification; speciation; and 3D structural determinations. To determine elemental composition by MS means to loss the largest part of the analytical qualitative, quantitative and structural information.
Please, consider the following work, together with the reference section therein. In other words, the soft-ionization methods are recommendable.
Article Electrospray ionization mass spectrometric solvate cluster a...
No. An FID detector uses combustion and an MS relies on fragmentation and ionization. RI (refractive index) is a liquid or solid physical function.
Thank you Bojidarka B. Ivanova and Bruce Neagle ; I was refering to "retention indices (RI)" derived via Kovats Retention Index. I am attempting to compare my data (RI) with the literature values and NIST database.
YES!
The retention index is not dependent on the type of detector used - as it is relative retention of n-alkanes.
best regards,
GB
Again no. RI is a function of your column, flow rates, gases, individual machine, and other chromatographic conditions. Thus, your value can vary considerably from literature values.
However, they are an indication of what you can achieve when you optimize your chromatographic conditions. You may obtain the same chromatographic profile (order of peaks) but have a different RI.
Mr. Wau,
The chromatography is no dough a powerful method, but when we are talking about relatively simple analytes from the perspective of molecular structure. For instance, complex structurally similar derivatives or enantiomers, fail to be determined unambiguously by chromatography.
Please, consider in this context this work (chapter 2.) It deals with MS quantification of steroids using the aforementioned approach developed by us.. It is well known that chromatography, for instance, fails to quantify highly reliably steroids.
So, efforts on development of chromatographic protocols, for complex molecules are in general, no sense. Conversely, the new methodologies in the soft-ionization MS methods provide remarkable method performances. For instance, the analysis of steroid shown in the next book has shown r = 0.99995.
There is a short presentation of the book content, herein: https://zenodo.org/record/3606820
Book QUANTITATIVE RELATIONS AMONG TEMPERATURE, ANALYTE CONCENTRAT...
Bruce said "No" and "Yes" at the same time. For a specific instrument your retention index should be consistent regardless of whether the detector is a MSD or a FID. ON THE OTHER HAND if you shift to a different instrument even with the same column and type of detector the retention index may shift.
Dear Friends
Retention index will not change if you use different instrument!
Retention index on specific column will be the same here and if somebody in China will buy same column also there th retention index will be the same for example 1511. It is confirmed by several test methods used for gasoline characteristics. Please check the DHA method.
Regards
GB
Yes whatever your type of detector (FID, MS, ECD, NPD...), the RI will be the same as long as you are using the same column and a linear programming of the oven temperature.
In summary, here are some precautions to take:
- Keep the same type of column (DB5, DB1 etc., same brand, etc.)
- If you are working with an external calibration (e.g. with a reference of alkanes or ethyl esters etc.), depending on the type of your column (polar or non polar), analyse more or less often your reference of indices. If you are working on pretoleum products, the alkanes are inside..
- Use a progressive alkanes reference (E.g. with C11 and just after C12 and after C13, not
C11 and then after C18 and C23 etc.).
- Use a linear temperature ramp during product elution (do not use steps).
The little differences you could find between your own database and a NIST are usually due to the little differences of the chemical phase between your column and the one use to create the NIST db (brand, quality of the column...).
That's why if you want to increase the quality of the compound identification, the best solution is to cross the identifications obtained on a polar column and those on a non polar column with 2 databases of compounds.
Retention Index of a chemical compound is independent of analytical conditions whereas retention time will change with conditions. The RI will remain always a constant on a given stationary phase and can change when the stationary phase is changed. We establish the RI of a compound with the help of n-alkane standards and it is a more authentic way of identifying a compound rather than identifying it on the basis of RT.
You can ask this to SAIF expert in India. About SAIF see details on internet.
The type of detector makes no difference to retention index; it is a property of the analyte on a particular stationary phase under a particular set of chromatographic conditions. Anyone who says otherwise is wrong. Anyone who addresses the differences in the information generated by an MS and an FID is not answering the question.
As Peter points out, the original question is not thought out and demonstrates a lack of understanding of the analytical techniques used. Both FID and MS detectors have nothing to do with questions about retention index, nothing. RI is related to methods, not detectors. Detector choice is not relevant.
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