EVIDENCE LIBRARY
Can Headspace GC-FID Quantify Vitreous Ethanol Reliably? A 2025 Validation Study’s Limits
A 2025 vitreous ethanol HS-GC-FID study reported a 0.15–2.50 mg/mL range and 3.60% analytical uncertainty—not proof of antemortem BAC or impairment.
Quick answer: Headspace gas chromatography with flame-ionization detection (HS-GC-FID) can directly measure ethanol in vitreous humor when the laboratory has validated the procedure for that specimen, concentration range, and reporting purpose. In a 2025 method-development study, Mihajlović and colleagues reported a vitreous-ethanol working range of 0.15–2.50 mg/mL, a calibration correlation coefficient of 0.9989, and expanded analytical measurement uncertainty of 3.60%. These are method-performance findings. They do not prove that a decedent drank alcohol, establish the decedent’s earlier blood alcohol concentration (BAC), diagnose impairment, or determine a cause of death. The correct forensic question is what the vitreous measurement establishes—and what case-specific evidence remains necessary.
What did the 2025 study actually test?
The primary investigation was a laboratory method-development and validation study, not an alcohol-administration experiment or a prospective study of intoxication deaths. The researchers developed a headspace GC-FID approach for ethanol in vitreous humor, the gel-like intraocular fluid sometimes available during a postmortem examination. They collected ethanol-negative vitreous specimens from seven deceased individuals, pooled the matrix, prepared ethanol-fortified validation samples, and tested selectivity, calibration, precision, recovery, stability, detection limits, and measurement uncertainty.
That distinction defines the evidence. Fortifying a tested matrix with known ethanol amounts makes it possible to evaluate whether a method recovers those amounts with acceptable repeatability. It does not recreate an actual decedent’s drinking history, postmortem interval, microbial activity, specimen preservation, or site-to-site distribution of ethanol. The investigators’ methods and numerical results appear in their complete original article: Mihajlović et al., Open Medicine (2025), DOI 10.1515/med-2024-1123.
Why is vitreous humor a different analytical matrix from blood?
Blood and vitreous fluid are physically different specimen types. A laboratory may have a robust blood-ethanol procedure without having demonstrated that precisely the same specimen preparation, calibration, matrix controls, and acceptance criteria apply to vitreous humor. Viscosity, sample homogeneity, specimen volume, storage, and matrix-dependent partitioning can matter to headspace analysis. A properly designed vitreous method must address those factors using vitreous matrix—not merely assume that performance in blood transfers automatically.
Vitreous sampling can add a valuable, independently collected source of ethanol information in a death investigation. It should not be described as an infallible sample or a direct proxy for living whole-blood BAC. Results become more informative when the complete file also contains appropriately collected blood, urine, chain-of-custody records, autopsy findings, and relevant circumstances. For the broader specimen issues, see the site’s postmortem toxicology framework.
How did the investigators measure ethanol in vitreous fluid?
The authors used a sealed-vial headspace procedure. Ethanol in a prepared vitreous sample partitions into the gas phase above the liquid during heating; the instrument samples that vapor, separates the compounds chromatographically, and measures the ethanol detector response. The method used n-propanol as an internal standard and quantified ethanol from the ethanol-to-internal-standard peak-area relationship. The reported ethanol and n-propanol retention times were approximately 2.13 and 2.47 minutes, respectively, under the studied system.
An internal standard helps control variation in preparation and instrumental response, but it is not a guarantee of proper analyte identity. A case review still asks whether the tested extract showed adequate separation from other volatiles, whether blanks were acceptable, and whether the internal-standard response remained within the laboratory’s decision rules. Because n-propanol can also be relevant in decomposed specimens, the laboratory should justify its internal-standard choice and its interference assessment for the specimens it actually accepts. This experiment specifically did not rely on putrefied cases to establish its performance.
More generally, GC-FID identifies and quantifies separated volatile peaks within a validated analytical method. It is not a behavioral instrument and does not observe intoxication, driving behavior, or the time alcohol entered the body. For the general alcohol-testing method, see blood alcohol testing by headspace GC-FID, while remembering that the study under discussion concerned vitreous specimens.
What were the reported validation numbers—and what do they mean?
The findings below summarize the authors’ reported validation values rather than an independent revalidation of their instrument. In particular, a detection limit, a limit of quantification, and the established routine working range answer different questions and should never be treated as interchangeable.
| Validation measure | Reported study value | Defensible interpretation |
|---|---|---|
| Working measurement range | 0.15–2.50 mg/mL vitreous ethanol | The study’s stated quantitative application window; do not assume performance outside it. |
| Calibration correlation | r = 0.9989 | Reported close linear association, not proof of uniformly accurate results at every point. |
| Limit of detection | 0.005 mg/mL | A reported ability to distinguish signal from baseline; not a validated case-reporting threshold. |
| Limit of quantification | 0.017 mg/mL | A calculated lower quantification limit, distinct from the 0.15 mg/mL stated working range. |
| Repeatability at 1.0 mg/mL | Approximately 0.5672% relative standard deviation across ten determinations | A repeatability observation at one tested concentration, not total forensic uncertainty. |
| Expanded analytical uncertainty | 3.60% (coverage factor 2) | A reported laboratory-method uncertainty estimate, not uncertainty in an earlier living BAC. |
A crucial qualification: High correlation is not a stand-in for bias, accuracy, selectivity, or uncertainty at a decision threshold. Laboratories should document calibrator residuals and acceptance criteria, recoveries by concentration, quality-control performance, and the procedure used to calculate the uncertainty budget. The paper reports numerical calibration details that deserve reconciliation against the original analytical records before a laboratory adopts those exact parameters. Readers should not treat this single study’s numeric estimates as a certification of another laboratory’s procedure.
What do recovery and repeated measurements show?
The investigators fortified vitreous matrix at five target levels—0.20, 0.50, 0.75, 1.00, and 2.50 mg/mL—and measured three preparations at each level for their recovery assessment. They also conducted ten repeat determinations around a 1.00 mg/mL target. The paper’s overall accuracy summary was 100.11% and its repeatability analysis reported an RSD near 0.57% at that tested target.
A recovery close to 100% is evidence that the method can measure fortified samples near their known prepared concentrations in those conditions. It does not mean that a future result has exactly zero bias or that an autopsy specimen will be stable after any handling history. Nor does a small repeatability RSD quantify errors from collection, labeling, decomposition, calibration drift, or a possibly inappropriate reporting decision. Those questions require additional records.
The method validation also discussed short-term handling, autosampler stability, three freeze–thaw cycles, and working-solution storage. These experiments inform a laboratory’s local protocol; they do not justify assuming that every field-collected vitreous sample remains unchanged for an unbounded period. Case records should identify actual storage temperatures, processing times, freeze–thaw history, container conditions, and any deviations from the locally verified procedure.
What evidence does the study not provide?
The central limit is not a weakness in chromatography. It is the distinction between accurately measuring ethanol in vitreous and inferring what happened in a living person. The research did not measure living subjects’ simultaneously obtained whole-blood BAC, establish any individual vitreous-to-blood conversion factor, validate a retrospective timeline from death to alcohol ingestion, or test actual cognitive or motor performance. A scientifically competent laboratory can answer an analytical question without answering those additional forensic questions.
| Question in a forensic case | What this experiment contributes | What remains unproved |
|---|---|---|
| Is ethanol present in vitreous humor? | A studied technique for detecting and separating an ethanol signal in vitreous matrix | The quality and authenticity of a particular case specimen |
| How much ethanol is in that fluid? | Reported calibration, recovery, repeatability, and analytical uncertainty | Case-run controls and lab-specific validation of the reported number |
| Was ethanol present before death? | An alternative specimen that may be compared with blood and urine | Whether this individual had antemortem ingestion versus postmortem or procedural artifacts |
| What was the person’s living whole-blood BAC? | No validated person-specific conversion or historical measurement | A precise antemortem concentration or back-calculated timeline |
| Was the person impaired or did alcohol cause death? | No functional, clinical-outcome, or causation experiment | Performance, clinical significance, legal impairment, contribution, or cause of death |
Can the 3.60% uncertainty figure be used as an exact BAC margin?
No. The authors’ 3.60% expanded uncertainty is a property of the evaluated vitreous analytical method under specified conditions. It is not a universal error percentage for all postmortem ethanol results. More importantly, antemortem BAC estimation has biological and case-history sources of uncertainty that this analytical number does not contain. Multiplying a vitreous concentration by a fixed ratio and attaching ±3.60% would incorrectly combine a method uncertainty estimate with an independently unvalidated conversion.
For a disputed case, a defensible uncertainty assessment should identify the laboratory’s analyte-specific validated range, QC acceptance, reported units, calibrator traceability, repeat measurements, recovery and extraction effects, instrument uncertainty, and uncertainty model. It must then distinguish those analytical components from postmortem formation or diffusion, collection and storage changes, individual physiology, and uncertainty about when drinking may have occurred.
Does an ethanol-positive vitreous result establish that drinking caused a fatal incident?
No. A verified positive result establishes an analytical finding in the submitted vitreous specimen, assuming specimen identity and quality are supported. Whether ethanol was ingested before death calls for additional investigation. Whether it impaired judgment, coordination, or consciousness is a different question again. Whether it caused or contributed to a collision, fall, drowning, poisoning, or other death requires a case-specific integration of scene evidence, pathology, clinical records when available, toxicology from multiple matrices, and relevant temporal facts.
Interpretation may be particularly complex with decomposed remains or when autopsy specimens have different collection sites, preservation, or handling histories. The validation matrix here came from ethanol-negative deceased donors and was fortified for laboratory testing. It did not reproduce the full spectrum of decomposition states or microbial activity encountered in casework. The correct use of the method is to improve confidence in what was measured, not to eliminate uncertainty the experiment did not study.
What should counsel or a consulting toxicologist request from the laboratory?
A useful technical review begins with the complete chromatographic record and applicable standard operating procedure, rather than a single final concentration. Request the matrix-specific validation package; instrument and headspace preparation conditions; the chain of custody, autopsy collection record, specimen volume and tube type; storage and freeze–thaw history; chromatograms and peak integrations; calibration levels and acceptance rules; blank and QC results; internal-standard responses; replicate agreement; and the calculation of measurement uncertainty. Where independent columns or confirmatory procedures are part of the accredited method, review those records as well.
The laboratory should also disclose the reporting range, any dilution or repeat analyses, evidence of potential interfering volatiles, and how it treats results near a lower quantification threshold. A low numerical ethanol finding should not be translated into a categorical statement of “no alcohol” without knowing the reportable detection and decision limits. Likewise, an ethanol-positive finding should not be converted into a specific drinking-time or impairment opinion without an evidentiary basis beyond the chromatogram.
Sampling considerations begin before the chromatograph is turned on; the site’s specimen collection and handling guide provides the related forensic framework.
Frequently asked questions about vitreous ethanol validation
1. Is vitreous humor the same as blood for ethanol testing?
No. It is a separate biological matrix. A vitreous ethanol concentration is a measurement in vitreous fluid, not a direct whole-blood BAC. Matrix-specific method validation and interpretive caution are required.
2. Does GC-FID prove that ethanol was present before death?
GC-FID can support the analytical identification and quantification of ethanol in the submitted sample. Timing and origin of ethanol require corroborating specimen and circumstances; the chromatogram alone cannot establish them.
3. Why are the LOD and LOQ below the working range?
The paper calculated a 0.005 mg/mL detection limit and 0.017 mg/mL quantification limit, but stated the operational range as 0.15–2.50 mg/mL. A low calculated limit is not permission to report quantitative case results below the laboratory’s fully supported validated range.
4. Does a correlation coefficient of 0.9989 establish full accuracy?
No. Correlation describes association in the calibration response. Bias, recovery, residuals, precision, specificity, blanks, and quality-control results are additional questions, especially near a consequential cutoff.
5. Can I apply ±3.60% to convert vitreous ethanol into living BAC?
No. That value is the authors’ expanded uncertainty estimate for their analytical method, not a validated uncertainty bound for postmortem-to-antemortem conversion or individual BAC reconstruction.
6. Did the researchers study severely decomposed remains?
The validation described pooled ethanol-negative vitreous material from seven deceased donors fortified with prepared ethanol concentrations. It did not establish accuracy across a case series spanning severe decomposition or prove that decomposition artifacts would be excluded in every autopsy specimen.
7. Can this study establish intoxication, driving impairment, or cause of death?
No. There was no driving, cognitive, motor-performance, or cause-of-death endpoint. The evidence supports method evaluation for a particular specimen and analyte, not a retrospective legal or medical conclusion about a person.
Bottom line: reliable measurement is necessary, but interpretation is a separate step
Mihajlović and colleagues provide a useful original example of developing and characterizing a vitreous ethanol HS-GC-FID method. The valuable contribution is a reported analytical range, sensitivity and recovery assessment, repeatability observations, and an uncertainty estimate for the measurement itself. The limitations are equally important: fortified pooled vitreous specimens are not a validation of person-specific antemortem BAC, impairment, drinking time, or causation. A forensic opinion should preserve that boundary and be traceable to the actual laboratory and case records.
Primary scientific source: Mihajlović F, Andrić I, Slović Ž, Vujović M, Piskulić K, Đorđević S. Development and validation of headspace gas chromatography with a flame ionization detector method for the determination of ethanol in the vitreous humor. Open Medicine. 2025;20(1):20241123. https://doi.org/10.1515/med-2024-1123.