NIST Expands Its Library of ‘Chemical Fingerprints’ to Identify Unknown Substances

Vials of some of the chemicals analyzed in the NIST mass spectral database.

Whether you're a researcher stumped by a mystery compound or a manufacturer perplexed by an unknown substance, there's a major resource you can rely on: a library of chemical fingerprints, known as mass spectra, that the National Institute of Standards and Technology (NIST) has maintained for decades.

Now, NIST has released the latest update to that library, which industry experts, forensic scientists and others have used since 1988 to identify unknown substances in food, drugs, cosmetics, the environment and even space rocks.

The expanded library, formally known as Standard Reference Database 1A, contains mass spectra measured from hundreds of thousands of compounds.

NIST scientists generate chemical fingerprints using a mass spectrometer, an instrument that ionizes and shatters a compound into charged fragments and then sorts those fragments by their mass-to-charge ratio. That gives researchers enough information to create a bar-chart-like graph known as a mass spectrum that is unique to that particular chemical.

This bar graph shows the chemical fingerprint for caffeine. To create the fingerprint, a mass spectrometer shattered the caffeine molecule into charged fragments and sorted them according to their charge-to-mass ratio. The height of each peak indicates the relative abundance of the fragment.

Researchers and manufacturers can use mass spectrometry to create their own bar chart of a mystery substance and run it through the NIST library to find a match.

"Just as a person may be identified by comparing their DNA to a database, a chemical compound may be identified by comparing its mass spectrum to the NIST database," said Bill Wallace, group leader of NIST's Mass Spectrometry Data Center.

Commonly called NIST26, the NIST Mass Spectral Library comes preinstalled on many commercial mass spectrometers. Users can purchase the updated library from their instrument manufacturer or other independent distributors.

To ensure that the updated library meets NIST's standards, NIST scientists use a comprehensive, software-based evaluation process that relies on decades of experience.

One of the world's largest mass spectral databases, the NIST26 library has two main components. The Electron Ionization (EI) Library contains fingerprints of compounds that are easily vaporized. Roughly 35,000 new compounds have been added to this library, for a total of over 382,180. The Tandem Library is used to identify nonvolatile compounds that dissolve in liquids. This library has 17,000 new compounds for a total of 68,635 substances.

A NIST researcher injects a sample into a mass spectrometer, a laboratory instrument that scientists use to identify unknown chemical compounds.

Compounds added to the new version of the NIST library include:

• Minor cannabinoids, trace chemicals hidden inside the cannabis plant that are being explored for medical uses, including pain relief.
• Nitazenes, a potent class of opioids increasingly associated with fatal drug overdoses.
• Thiophenes, a class of ring-shaped, sulfur-containing organic molecules found by NASA's Curiosity rover and which are a possible signature of ancient life on Mars.
• Complex organic compounds known as alkylated polycyclic aromatic hydrocarbons (PAHs), found in dust from the near-Earth asteroid Bennu; PAHs may have seeded the infant Earth with some chemical compounds necessary for life.
• Plant-based derivatives of serotonin and dopamine, known respectively as N-(p-Coumaroyl) serotonin and N-Methyldopamine, which are being studied as potential therapeutic agents due to their antioxidants and anti-inflammatory properties.
• An expanded set of per- and polyfluoroalkyl substances (PFAS), "forever chemicals" found in the environment.

Interested individuals can visit the Mass Spectrometry Data Center's newly updated website chemdata.nist.gov for more information.