Short answer: A GC-MS report describes compounds detected in a particular sample under a particular laboratory method. It can help compare composition and investigate identity, but it is not a stand-alone certificate of purity or safety. First check that the report names your product and lot; then look at how the laboratory identified and measured the listed compounds.

Start with the sample name and lot

Start with the sample, not the largest peak. Record the product name, botanical material, plant part, extraction claim, supplier, lot, container, receipt date, storage, and chain of custody. Then preserve the laboratory’s method, instrument, column, run conditions, calibration or quality-control information, library version, retention-index approach, and analyst comments. A report that omits those fields may still be useful as a screening document, but its conclusion must stay narrow.

NIST’s WebBook and EI/retention-index library documentation explain the reference records used in identification. Babushok and colleagues provide retention-index data for plant-oil constituents. EPA Method 8270E illustrates calibration and quality-control requirements in its own semivolatile environmental methods; it is not an essential-oil purity specification. Read each reference within that scope before transferring an identification or percentage.

What peaks, matches and percentages mean

Report itemWhat it may supportWhat it cannot prove alone
Chromatographic peakA detected signal at a retention position under the stated method.The compound’s identity, concentration, source, or safety without further interpretation.
Mass spectrumA pattern that can be compared with a reference spectrum.An uncontested identity when co-elution, library limits, or sample preparation are unknown.
Library or index matchA candidate identification under the library and method conditions.Authenticity, geographic origin, adulteration status, or therapeutic value.
Quantitative resultA reported amount within the validated range and uncertainty of the method.Quality of a different lot, a complete impurity profile, or suitability for a person.

Check method fit before comparing oils

Two reports are comparable only when the sample type, preparation, separation method, instrument, standards, identification rules, and reporting conventions are sufficiently aligned. Steam-distilled oil, expressed peel oil, absolutes, isolates, fragrance blends, and diluted products can produce different profiles. A missing peak may reflect the method or reporting threshold; a new peak may need confirmation rather than an immediate accusation of adulteration.

Ask whether the lab used authentic reference material, an appropriate library, retention-index confirmation, replicate or control runs, and a stated limit of detection or quantitation. Ask what “not detected” means in that report. Do not infer that a compound is absent from a sample merely because it was not listed, and do not infer that a listed compound is the only component that matters.

Questions to send to the supplier or laboratory

  1. Identify the exact sample, lot, container, supplier, botanical name, plant part, extraction method, and chain of custody.
  2. Copy the instrument, method, column, run conditions, standards, quality controls, library, and report version.
  3. For each important peak, record retention data, spectral match, confidence language, quantitative basis, and unresolved ambiguity.
  4. Compare like with like: same material, preparation, method, reference, endpoint, and decision threshold.
  5. Send authenticity, contamination, regulatory, or safety decisions to a qualified laboratory or responsible authority.

For example, suppose a supplier advertises “GC-MS tested” and shares a report listing a major constituent at 40%. Before using that figure, ask whether it is a calibrated concentration or a relative peak-area percentage. Also check the sample lot and the laboratory’s identification notes. A percentage printed beside a compound name does not, by itself, establish the amount of that compound in your bottle or prove the oil is unadulterated.

Also check whether the report describes the whole sample or only selected analytes. A short list of named constituents is not a complete composition, and a reference spectrum is not a chain-of-custody record. Preserve the analyst’s qualifications and any unresolved co-elution or library limitation alongside the result.

Where the evidence stops

This page does not certify an oil, interpret an incomplete chromatogram as fraud, provide a laboratory method, or convert chemical identity into a health claim. A signal, candidate match, validated result, product specification, and safety decision are separate records; the sample and method determine how far the conclusion can go.