FAQs

Analytic

1. We know that the same compound can be compared with each other in different treatment groups. So, for the same individual, can ionic strength between different compounds identified be compared on a relatively quantitative level? Or need an internal reference?

Different compounds are generally not available for relative quantitative comparison. Because of the different responses of different compounds, they are often incomparable. For example, if the concentrations of Compounds A and B are the same in the sample, but the response rate of Compound A is 100 times that of Compound B, then the response of Compound A detected by mass spectrometry is higher than B, but does not mean that the concentration of A is higher than B. Since the response rate of a compound is generally constant, the response of a compound in different samples is positively correlated with its concentration in the sample. The same compounds are comparable in different samples.

2. If there are many substances with the same mw value and RT, what methods are generally used to further identify the substance?

If the formula is similar and the structure is similar, the scores are very close, which is difficult to distinguish from the full spectrum level. Generally speaking, it is acceptable to only identify the large category of these substances and the biological functions of them.

3. How can we verify the identification results of the metabolites?

The identified metabolites need to be verified by the standard before they can be confirmed. Why use the standard verification: Since the spectra of the compounds under different instruments or different experimental conditions vary greatly, the results obtained by database matching are for reference only; and according to the 2007 MSI (Metabolomics Standards Initiative Metabolism Standards Program, proposed by the Metabolomics Association) proposed principle of compound identification, in order to truly confirm the compound, it is still required to compare the sample with the standard under the same experimental conditions to obtain the spectrum and peak time. The test conditions are the same as those established when building BMDB Library database.

4. Why does the differential metabolite have NULL, empty values, or map* numbers in the corresponding pathway? This means that the metabolic pathway marked NULL can not be found in the database or you need to go to the KEGG database to search for yourself? How to search?

Not all metabolites are annotated to the pathway in the KEGG database. NULL means no annotation to the pathway; empty values indicate annotations to the pathway but not the specific corresponding species, so it is deleted here; map* Numbered means the metabolic pathway that is annotated to, and belongs to the specific species.