The mass spectrum for the synthetic opioid, fentanyl. Photo: NIST

Forensic scientists can sometimes feel like they are fighting a losing battle when it comes to drugs. The opioid crisis continues to grow, and drug manufacturers continue to stay a step ahead by slightly modifying the chemical structure of synthetic designer drugs to avert detection.

But, NIST scientists are fighting back—equipping forensic analysts, as well as other researchers, with modern day tools and algorithms that may finally allow them to be the ones a step ahead.

On June 6, 2017, coinciding with the American Society for Mass Spectrometry conference in Indianapolis, NIST released the latest version of its widely used Mass Spectral Library, adding molecular fingerprints from more than 25,000 compounds, bringing the total number to more than 265,000.

But the number is not the important part of this upgrade.

“In [this release], we have something called the hybrid search, which is a new kind of mass spectrometry search method that can reliably identify compounds—even if they are not in your library—that differ from your library compound by one chemical group that doesn’t affect the fragmentation, like fluorine or methyl,” explained Stephen Stein, the NIST chemist who oversees the library. “Many of the designer drugs have derivatives. With one fentanyl in the library, you can theoretically identify hundreds of others. If the functional group doesn’t change, the signature doesn’t change, so you can match that. It increases the coverage of your library with just an algorithm.”

The compounds in this upgrade include dozens of synthetic cannabinoids—aka “synthetic marijuana”—that can cause psychotic episodes, seizures and death. Also included are more than 30 types of fentanyl, the synthetic opioid that is driving an epidemic of overdoses nationwide.

Stein told Forensic Magazine his group didn’t set out to intentionally add drug compounds to the library, but the need for such a thing was clear.

“We try to be comprehensive,” he said, regarding which compounds to focus on when pursuing a major upgrade. “We don’t have too many more pesticides or industrial chemicals to add, so the biggest type of compound that people need and want are drug-related.”

More tools

The NIST spectral library is used by scientists in virtually every industry—clinical, environmental, food, fragrance, energy, etc.

As Stein points out though, forensic scientists have another tool at their disposal—one he believes is underutilized.

AMDIS, as it’s called, was developed at NIST with the support of the DoD to reduce the effort involved in identifying compounds by gas chromatography mass spectrometry (GCMS), which is often the method of choice for forensic scientists given its reproducibility factor.

The program extracts the spectrum of each component in a mixture analyzed by GCMS or liquid chromatography mass spectrometry (LCMS), and identifies target compounds. AMDIS is an integrated set of procedures for first extracting pure component spectra and related information from complex chromatograms, then using this information to determine whether the component can be identified as one of the compounds represented in a reference library. The library could be your own, it could be NIST’s, or it could be one of a third-party.

Be it targeted or untargeted analysis, Stein leans toward the use of a large, comprehensive library.

“One interesting thing about a big library is all the compounds that could masquerade as false positives are probably in a big library. So, you can show the uniqueness of your spectrum only by searching against a large library,” he said.

But, he’s quick to point out libraries don’t identify compounds—people do.

“When you get a hit list, it always needs a manual confirmation,” Stein said. “Compounds’ spectra are too variable, they can be too similar, or there could be an analytical problem. In all cases, a human needs to look at a couple hits in the library and make a decision based on that.”

Humans are the ones that fuel NIST’s rigorous quality control measures for the Mass Spectral Library. According to Stein, his team first tries to obtain the highest-quality original spectrum “because there’s no substitute for that.” Every spectrum is then critically evaluated by at least two people. If they agree, the spectrum gets added to the library. If they disagree, the spectrum is either resolved with a third-party, or is completely left out of the library if a high level of confidence cannot be reached. The last stop for a spectrum includes running it through various software methods that match consistency with structure or chemical formula. If a spectrum passes all these tests, it’s added to the archives.

“We just want the compounds to give [scientists] good, confident identification when they find it in the lab,” Stein said.

NIST has been publishing its Mass Spectral Library since 1989.