chemistry

METLIN

METLIN is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand METLIN rather than just read about it. In short: The METLIN Metabolite and Chemical Entity Database is the largest repository of experimental tandem mass spectrometry and neutral loss data acquired from standards. The tandem mass spectrometry data on over 960,000 molecular standards (as of October, 2025) is provided to facilitate the identification of chemical entities from tandem mass spectrometry experiments.

Key takeaways

METLIN belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect METLIN to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of METLIN from memory before moving on to harder problems.

Reference excerpt

The METLIN Metabolite and Chemical Entity Database is the largest repository of experimental tandem mass spectrometry and neutral loss data acquired from standards. The tandem mass spectrometry data on over 960,000 molecular standards (as of October, 2025) is provided to facilitate the identification of chemical entities from tandem mass spectrometry experiments. In addition to the identification of known molecules, it is also useful for identifying unknowns using its similarity searching technology. All tandem mass spectrometry data comes from the experimental analysis of standards at multiple collision energies and in both positive and negative ionization modes. METLIN serves as a data management system to assist in metabolite and chemical entity identification by providing public access to its repository of comprehensive MS/MS and neutral loss data. METLIN's annotated list of molecular standards include metabolites and other chemical entities, searching METLIN can be done based on a molecule's tandem mass spectrometry data, neutral loss masses, precursor mass, chemical formula, and structure within the METLIN website. Each molecule is linked to outside resources such as the Kyoto Encyclopedia of Genes and Genomes (KEGG) for further reference and inquiry. The METLIN database was developed and is maintained solely by the Siuzdak laboratory at The Scripps Research Institute.

Constantly evolving Since its initial implementation in the early 2000s, the freely available METLIN website has collected comments and suggestions for improvements from users in the biotechnology, pharmaceutical and academic communities ultimately resulting in functionally useful technology for metabolomics as well as hundreds of thousands of other molecular entities. The METLIN interface allows researchers to readily search the database and characterize metabolites and other compounds through features such as accurate mass, single and multiple fragment searching, neutral loss and full spectrum search capabilities. The similarity searching feature introduced in 2008 was designed to expedite the identification process of unknown molecules. Also, METLIN has been used to create a novel multiple reaction monitoring (MRM) library of precursor to fragment ion transitions. The METLIN-MRM transition repository for small-molecule quantitative tandem mass spectrometry was designed to facilitate data sharing across different instruments and laboratories. A new version of generating MRM transitions was introduced in 2026 as uMRM [1], and takes advantage of the original METLIN-MRM concepts. uMRM however is designed to remove isotopes and in-source fragments (ISF) prior to generating MRMs using a spline-fitting method using multiple collision energies. The METLIN database is implemented in the cloud to enable users throughout the world. In addition to expanding the tandem mass spectrometry database, METLIN is designed to search tandem mass spectrometry data, precursor mass, chemical formulas, compound names among other search capabilities. METLIN has also been implemented with cognitive computing applications. The tandem MS high-resolution ESI-QTOF MS/MS data on now over 960,000 distinct chemical entities, includes mass spectral collision-induced dissociation data at four different collision energies, in both positive and negative ionization modes.

References

External links Official website

Worked examples

Example 1 — a first encounter with METLIN

Start with the simplest possible case. Write down what METLIN claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to METLIN before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about METLIN ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of METLIN

In research: METLIN appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses METLIN in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: METLIN is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical databases, Metabolism, so understanding it makes those chapters shorter.
In everyday life: Look for METLIN outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study METLIN in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what METLIN means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain METLIN out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is METLIN in simple terms?

Why does METLIN matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study METLIN?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on METLIN.