The peak area of chromatograph from GC-FID and GC-MS varies considerably for the same essential oil sample. Of course the identification technique is different in both the techniques, but GC-FID is preferred for percentage calculation.
Please re-phrase your question. What do you mean by accurate? Integration accuracy, quantification accuracy... ?
Peak area alone is not an indication of accuracy. It is a measurement method, based on what and how your integration parameters are setup. With the right method, both FID and MS (EI) detectors (alone or in-series) are very useful tools to obtain a range of information about volatile samples. Neither is a universal detector. There are some things that one may pickup and not the other (or both detectors may not "see" anything where something actually exists). You are comparing two completely different detection methods to each other. FID and EI-MS are very different techniques and can and do provide different types of response. The GC technique, detector chosen, method and most importantly of all, the applicability to each sample being analyzed all contribute to the results. Are you trying to decide which detector to use for calibration purposes? If so, please construct a full calibration table for the samples (and stds) of interest. This would need to be constructed to cover the range(s) analyzed. The data obtained would be used to construct a calibration curve to assess your actual samples. This would provide raw data for different concentrations and their responses so you could work out a calibration fit.
GC-FID is better for quick quantitative analysis of samples containing compounds of a similar type and composition (e.g., alkanes, aromatics, alcohols, etc.). In this case, a percentage of every analyte may be determined by normalization (Wi=Si/Stotal) because response factors of each compound should be the same. With GC-MS, analysis by normalization is possible, but with a lower accuracy because every compound has its own detector response factor. However, using GC-MS, you can actually detect every compound present in the sample while FID will not respond to water and many other compounds. I.e., if you inject 40% ethanol solution in water to GC-FID, you will see only ethanol and may conclude that its concentration is 100% which is of cource not true. With GC-MS, you will see both peaks, but water peak will probably be smaller because GC-MS sensitivity to water is lower compared to most other analytes. For best accuracy using both methods, external (or internal) standard calibration is anyway required. Standard addition calibration is another option.
Hi, at our Lab. ,we will prefer to do it with GCMS, if we do it using GC FID, we can not know the observed - peak by GC FID is pure and not contaminated with other compounds, so if it is the case, the calculation might be bias. By Using GC MS, we can confirm the purity and identity of all TIC peaks, if the peak contaminated, we can know from the MS spectra. For doing quantification we usually do using SIM with GC MS. Some times we did too using GC FID, but to confirm the number of components we did GC FID at least in three different conditions, to check whether the (target) peak(s) is(are) not contaminated with other compounds. Best regards
In general the signal per unit mass for an FID differs less between different organic compounds than it does for an MS in full scan. The notable exceptions are that molecules with a high content of oxygen or halogens give a poor response with FID. In an essential oil I would not expect to find compounds with markedly divergent signals per unit mass on either an FID or an MS, which makes me suspect that you have another source of discrimination. Assuming of course that you running the MS in full scan.
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