Table 5.
Top 20 metabolites with highest loading in LD1 in PCDA analysisa
| Rank PCDA | GC × GC–MS | GC–MS | ||
|---|---|---|---|---|
| Compoundb | Loading LD1 | Compound | Loading LD1 | |
| 1 | Campesterol* | −4.41 | Campesterol* | −4.55 |
| 2 | M0617 (unsaturated fatty acid methyl ester) | −4.36 | GA0502 | −4.37 |
| 3 | M0480 | −4.29 | 1,2-Diglyceridec | 4.28 |
| 4 | M0071 | −4.27 | 1-Palmitoyl-l-alpha-lysophosphatidic acidc | −4.22 |
| 5 | Linoleic acid* | −4.17 | 1-Palmitoyl-sn-glycero-3-phosphocholine | −4.18 |
| 6 | M0535 (purine) | −4.04 | Arachidonic acid* | −4.03 |
| 7 | Taurine* | 4.00 | Linoleic acid* | −4.00 |
| 8 | Tyrosine* | −3.99 | GA0123c | −3.91 |
| 9 | M0221 (amino-organic acid) | −3.98 | Beta-Alanine | −3.83 |
| 10 | M0444 | −3.92 | GA0514 | −3.82 |
| 11 | M0651 | −3.91 | GA0510 | −3.81 |
| 12 | M0593 (monoglyceride) | −3.90 | C20:1 fatty acidc | 3.80 |
| 13 | Spermidine* | −3.85 | Pipecolinic acidc | −3.78 |
| 14 | M0182 (piperidine) | −3.84 | Fumaric acid | −3.77 |
| 15 | M0550 | −3.84 | 1-Monolinoleoylglycerol | −3.77 |
| 16 | M0283 (pyrrolidinone) | −3.81 | 1-Monooleoylglycerol* | 3.76 |
| 17 | 1,5-Anhydro-d-glucitol* | −3.80 | Gluconic acid* | −3.75 |
| 18 | M0600 (polyunsaturated fatty acid) | −3.79 | GA0520c | −3.71 |
| 19 | M0597 | −3.75 | GA0507 | −3.71 |
| 20 | M0307 (deoxyglucose or isomer) | −3.72 | Spermidine* | −3.70 |
aIn bold: metabolites present in both top 20s, in italics: metabolites present in both datasets, but not the top 20 of GC × GC–MS data. Metabolites marked with an asterisk are identified with authentic standards, other metabolites given a name are annotated via their mass spectra (more information in Sect. 2). The retention times and quantification masses of unknowns (M-coded and GA-coded metabolites) are listed in the Supplement (S-Table 2)
bTentative annotation via MS library match or characterization of type of metabolite based on the mass spectrum are given in brackets
cMetabolites were not identified in the GC × GC–MS data set, most likely due to uncertainty in the assignment of the identity (no reference standard available and mass spectrum not unique enough). Only number 3 and 4 from GC–MS were not measured with GC × GC–MS, because their elution temperature was too high. Most probably all other metabolites are present in the 2D data set, but under a different name (M-code). However, none of the unknown top 20 metabolites from the GC–MS data set were present in the top 20 of the GC × GC–MS data (checked manually via mass spectra)