Method: Fatty Acid Composition (FAME-GC)
Test: Fatty Acid Composition Status: Published method overview.
This overview explains how a sample becomes a fatty-acid report, from preparation through measurement and calculation. It introduces the chemistry and reporting approach; your sample's supporting record connects that approach to the laboratory work and data behind your result.
1. Scope and principle
Total lipids are extracted from the sample, converted to fatty acid methyl esters (FAMEs), and separated by capillary gas chromatography with flame ionization detection (GC-FID). Each fatty acid in the mix elutes at a characteristic retention time and is quantified against a calibration built from a multi-component FAME reference standard. Results are reported as weight percent of total fatty acids (wt% total FA), with derived indices calculated from the quantified profile.
FAME derivatization and GC-FID quantification of food fats is the classical, widely published approach (the family of AOCS/AOAC official methods and standard oil-chemistry references). We follow that established practice.
2. Sample preparation
- Homogenization. The received sample is brought to a uniform state (melted-and-mixed for fats, homogenized for eggs/meats/processed foods) so the aliquot represents what you mailed.
- Lipid extraction. Total fat is extracted with an organic solvent system per standard lipid-extraction practice; extraction efficiency is verified in method validation and checked with control materials.
- Derivatization. An aliquot of extracted fat is transesterified to FAMEs (base-catalyzed methylation, with acid catalysis available where free fatty acids are elevated). FAMEs are the volatile, GC-stable form of each fatty acid.
- Internal standard. An odd-chain / non-natural FAME internal standard is added before derivatization to monitor extraction-to-injection recovery and support absolute quantification where the matrix warrants it.
3. Instrumental analysis (GC-FID)
- Injection: split injection onto a long, highly-polar capillary column (cyanopropyl polysiloxane phase — the standard phase class for resolving fatty acid isomers, including geometric and positional trans isomers).
- Separation: a programmed temperature ramp resolves ~30+ common food fatty acids from C4:0 through C22:6, including the trans isomer region.
- Detection: flame ionization detection; FID response is proportional to carbon mass and is calibrated per component rather than assumed equal.
- Identification: retention-time matching against the FAME standard mix, with retention-index confirmation for tricky peaks (conjugated linoleic isomers, trans monoenes). Where a peak cannot be confidently identified, it is reported as unidentified, not renamed.
4. Calibration
Quantification is anchored to a 37-component FAME reference mix with individual component certified values and stated certified uncertainties. Calibration runs bracket every sample batch; response factors are applied per component, because FID response is not identical across chain lengths, degrees of unsaturation, and isomer geometry. Calibration ages are tracked: a standard or control outside its acceptance window pauses the batch for investigation before results are released.
5. Replication and batch controls
- Samples are analyzed in replicate injections; within-run agreement is evaluated before reporting, and outlying spread triggers reinjection or rerun.
- Each batch carries a reagent blank (full chemistry, no sample) to catch contamination carried through extraction or derivatization, and a control material of known expected composition to verify the batch as a whole.
- Profile-level plausibility checks (buckets summing near 100%; marker fatty acids consistent with the declared sample type) run before a report is released.
6. Reporting
Reports present, per fatty acid: identity, wt% of total fatty acids, and relative precision. Summary lines report SFA, MUFA, PUFA, omega-6 and omega-3 subtotals, the omega-6 : omega-3 ratio, and trans fatty acids both as a total and broken out into individual isomers (natural ruminant trans vs. industrial-processed trans families are distinguishable by retention behavior). Derived indices (atherogenicity and nutritional ratios as applicable) are computed from the quantified profile, never measured independently.
7. Detection limits and data quality statements
Components at or near instrument/batch detection capability are reported as "not detected (< stated limit)" with the limit printed on the report. "Not detected" means below the stated limit in this matrix by this method — a measurement statement, never a claim of absence. Small percentages near the limit carry proportionally larger relative uncertainty, and reports note it in place.
8. Scope of interpretation
- Composition profiles can support comparisons with expected ranges for a product. Feeding practices such as "grass-fed" cannot be certified from composition alone because profiles overlap.
- FAME-GC reports fatty acids present in the extracted lipid; it does not identify non-lipid adulterants, contaminants, or origin geography directly.
- Reports are for personal information, not regulatory determinations.
9. Your sample's supporting record
Your full Computable Lab event graph is available alongside the report. This connected record lets you follow the laboratory work behind your sample and includes the actual instrument data trace and the analysis script used to calculate the reported percentages.
The record supports a closer examination of how the result was produced, whether you review it yourself or share it with an independent scientist. Contact us with your order ID to access it, or read more about our approach to quality.