When the State charges a Georgia driver with DUI-drugs, DUI-combination, or DUI less safe, the case often turns on a laboratory report. That report may look definitive. It is not. Behind the reported result is a method, an instrument, a library, a set of identification criteria, and a stack of raw data the jury never sees unless defense counsel asks for it.

“Science is the belief in the ignorance of experts. When someone says, ‘Science teaches such and such,’ he is using the word incorrectly. Science doesn’t teach anything; experience teaches it. If they say to you, ‘Science has shown such and such,’ you might ask, ‘How does science show it? How did the scientists find out? How? What? Where?’”
— Richard Feynman, What Is Science? (1966)

Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) are among the most powerful tools available to forensic scientists. Both combine chromatography, which separates the components of a complex sample, with mass spectrometry, which helps scientists identify and measure those components.

They are not interchangeable. The question in a DUI or controlled-substance case is not which machine has the better reputation. The question is whether the laboratory selected an appropriate method, properly validated that method, performed the analysis correctly, and produced data that scientifically support the conclusion reported.

Why this matters in a Georgia DUI-drugs case

Georgia DUI prosecutions involving blood or urine testing frequently rest on forensic identification of alcohol, prescription medications, synthetic opioids, benzodiazepines, cannabinoids, emerging drugs, or metabolites. A lab may report a compound as “confirmed.” That word should trigger discovery, not surrender.

If the method was wrong for the analyte, if the library was incomplete, if the peak was noisy, if the ion ratios failed, or if the quality-control samples do not support the result, the reported identification may be weaker than the certificate of analysis suggests.

GC-MS and LC-MS: related tools, different jobs

GC-MS is particularly effective for compounds that are sufficiently volatile and thermally stable. It has long been used to analyze controlled substances, solvents, ignitable liquids, volatile organic compounds, and certain drugs and metabolites.

LC-MS—and especially tandem mass spectrometry, or LC-MS/MS—is often better suited for substances that are polar, less volatile, thermally unstable, or present at extremely low concentrations. It is commonly used for prescription medications, synthetic opioids, benzodiazepines, cannabinoids, emerging drugs, and metabolites found in biological samples.

In some cases, complementary techniques provide stronger evidence than either technique alone. Forensic analytical chemistry is not a competition between instruments. What matters is whether the method was fit for its intended purpose and whether the resulting data support the conclusion.

A library match is not absolute proof

One of GC-MS’s recognized strengths is its ability to produce characteristic fragmentation patterns. A laboratory may compare the spectrum generated from an unknown substance with spectra contained in a computerized reference library.

That comparison can be valuable. A library “match” should not be mistaken for an absolute identification.

A simple way to think about a library match from Medusa Analytical independent laboratories.

Imagine trying to identify an unknown vehicle using a catalog that contains only Ford models. Even if the vehicle is actually a Honda or Chevrolet, the catalog will still return the Ford that looks most similar—because those are the only choices available.

A chemical reference library works in much the same way. The software compares an unknown spectrum with the substances included in its library and identifies the closest available match. If the correct substance is missing—or if the library is too limited—the system may return a convincing match that is nevertheless incorrect.

A library match is a useful investigative tool. It is not, by itself, conclusive proof of a substance’s identity.

The reliability of the comparison depends on:

• the quality and scope of the library
• the quality of the sample spectrum
• the laboratory’s identification criteria
• the availability of appropriate reference materials

A compound that is absent from a laboratory’s library cannot be accurately selected as the best match. Closely related substances may also produce similar fragmentation patterns, particularly when the analytical data are incomplete or the sample contains multiple compounds.

A scientifically supported identification should consider the entire body of evidence, which may include:

• retention behavior
• diagnostic ions and their relative abundance
• spectral quality
• reference-standard results
• calibration data
• blank and quality-control results
• potential interferences
• the laboratory’s validated identification criteria

The computer’s proposed match is one part of the analysis—not the final scientific judgment.

Counsel’s checklist: what to request from the laboratory

A final laboratory report often contains only a small portion of the information necessary to evaluate the analysis. Depending on the evidence and technique involved, attorneys should consider requesting:

• standard operating procedures
• the complete method-validation study
• calibration records and calibration curves
• chromatograms and underlying instrument data
• mass spectra or LC-MS/MS ion-transition data
• quality-control and blank results
• batch sequences
• integration records and audit trails
• internal-standard performance
• reference-material documentation
• instrument maintenance and performance records
• analyst notes and worksheets
• technical and administrative review records
• the laboratory’s identification and reporting criteria

The appropriate discovery request depends on the substance, method, instrument, and scientific issue in the case. In a Georgia DUI-drugs file, that request should be tailored—not copied from a generic form and forgotten.

Science under scrutiny: a chromatogram is data, not a verdict

Both GC-MS and LC-MS produce chromatograms showing the instrument’s response over time. Peaks appear as compounds move through the analytical system and reach the detector.

The presence of a peak does not automatically establish the identity or concentration of a substance.

An analyst may also need to evaluate:

• retention time
• peak shape
• signal-to-noise ratio
• diagnostic ions or transitions
• ion ratios
• internal-standard response
• calibration performance
• interferences
• blanks
• quality-control samples

A peak must satisfy the laboratory’s validated criteria before it can support a reported conclusion. Independent review should extend beyond the final laboratory report to the underlying analytical data.

The question to ask

Was the method appropriate, properly validated, correctly performed, and scientifically supported for this particular sample and analyte?

GC-MS may be the right tool for one analytical problem. LC-MS/MS may be better suited to another. In some cases, neither result is as strong as the State’s report implies until the raw data, validation file, and identification criteria are examined.

That is how DUI-drugs cases are actually tried: not by accepting a one-page confirmation, but by testing whether the science supports the charge.

Charged with DUI-drugs in Georgia?

If the State is relying on a blood or urine result, do not assume the lab work is beyond challenge. George C. Creal, Jr., P.C. concentrates in Georgia DUI defense, including cases built on forensic toxicology. We review the stop, the draw, the chain of custody, and the laboratory method that produced the number on the report. We also work with independent laboratories like https://www.medusaanalytical.com/

Free case evaluation: (404) 333-0706
Online: www.georgecreal.com
George C. Creal, Jr., P.C., Trial Lawyers
480 John Wesley Dobbs Ave NE, Unit 190
Atlanta, Georgia 30312

This article is for educational purposes only and is not legal advice. George C. Creal, Jr., P.C. is authorized to practice law in the State of Georgia. Information on this site is intended for DUI and related charges arising in Georgia. If your arrest occurred in another state, consult a licensed attorney in that state.