Dear researchers
I have a question concerning GC-MS!!!
we want to do an assay of short-chain fatty acids (SCFA) through GC-MS. these SCFA have been extracted from stools according to a well-adapted protocol but we don't have any standards and to order the standards it will take a lot of time. my question is: can we do an assay without any standard and then compare the spectra obtained with a specific database for SCFA?
if yes, what is the name of the specific database for this, and how to do it ???
Standards are not used for the fun of it in research. There must be some form of reference to guide the performance of a new thing; better or worse
If your fatty acids are not very exotic, you can use a GCMS library (e.g. NIST), combined with the retention index of your fatty acids (also available from NIST) to confirm the identity of your target. Having a reference compound is helpful for determining the retention time but not strictly necessary. For quantitative analyses, you will need to run a standard with a known purity to determine the detector response for each individual SCFA that you need to determine.
Have your machine been validated for its performance and results? Have some of the similar class of known compounds been run? As Dr. Alders says, you can go ahead and try the NIST based standards comparison after your sample run, but it would be better to have verified the RT with a known set of products (if few of them you have, or a known sample). Usually vendors supply some to check the machine's appropriate functioning and the RI retention index/indices.
It is best to have Standards but if You don't, first run the Alkane Series with Your Samples in the Batch and Calculate the Retention Indices, Use the AMDIS (Automated Mass spectral Deconvolution and Identification System) which come along with NIST library to get the pure Spectrum for your analytes and then You can compare these spectrums with the ones in the library and also compare the calculated Indices with the Indices in the Library. again it is not the best thing that You can do but could be an alternative when you don't have standards!!!
Yes. If the data base are obtained under the same conditions of the GC-MS spectra.
For identification, you can compare its spectra with library spectra, but for quantification all you need is standard. For time being, you can also use your another sample of known best purity/potency as a standard.
Yes, it's possible to make a comparison of GC-MS spectra with a database library, without using standards.For example, for the analysis of new drugs of abuse, sometimes we don't have standards.
Yes, you can compare GCMS spectra with already existing database library.
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