FTIR Peak Identifier — Free Infrared Spectrum Analysis Tool

Identifying functional groups from an FTIR spectrum traditionally means cross-referencing peak positions against printed correlation charts or multi-page reference tables. It's time-consuming, error-prone, and especially difficult for beginners learning to interpret spectra.

SpectralBench automates FTIR peak identification: upload your FTIR data, and the peak identifier detects absorption bands, matches them against a curated database of over 80 functional group entries, and returns ranked assignments with confidence scores. You can tune the sensitivity, inspect alternative assignments, and click any peak to highlight it on the chart — all without leaving your browser. Once you have identified your peaks, use the unit converter to express peak positions in wavelength or energy units, or the Beer-Lambert calculator to determine concentrations from measured absorbance values.

How It Works

Upload an FTIR spectrum in any supported format — JCAMP-DX, SPC, Bruker OPUS, CSV, or TXT. SpectralBench parses the file client-side and renders the spectrum on an interactive chart. The peak detector then applies a prominence-based algorithm to locate absorption bands, filtering out baseline noise and minor shoulders based on your sensitivity settings.

Each detected peak is matched against a curated database of over 80 functional group entries spanning common organic, polymer, and inorganic IR bands. Assignments are ranked by confidence — high, medium, or low — based on how well the observed wavenumber and band shape match the expected ranges for each functional group.

Click any peak in the results table to highlight it on the chart. Expand a row to see alternative assignments and potential interferents — other functional groups whose absorption ranges overlap. Adjust the prominence threshold to detect weaker bands, or reduce the max peaks count to focus on the most significant absorptions. All processing runs in your browser; your spectral data is never uploaded.

Understanding FTIR Peak Assignment

Infrared spectroscopy works because molecular bonds absorb infrared light at characteristic frequencies determined by the masses of the atoms and the stiffness of the bonds connecting them. These absorptions appear as peaks (or dips, in transmittance mode) in the spectrum, and each one corresponds to a specific type of bond vibration — stretching, bending, rocking, or wagging.

Functional group correlation is the practice of mapping observed peak positions to known absorption ranges for molecular groups such as O-H, C-H, C=O, and N-H. The infrared spectrum is conventionally divided into characteristic regions where specific bond types absorb, making it possible to identify functional groups even in complex mixtures. SpectralBench's database covers the most commonly encountered functional groups in organic chemistry, polymer science, pharmaceuticals, and environmental analysis.

While correlation charts provide a quick visual reference, automated FTIR functional group assignment goes further by considering exact peak positions, band shapes, and the relative likelihood of each assignment. This is especially helpful for students learning to interpret FTIR spectra and for researchers working with unfamiliar compound classes. For a comprehensive walkthrough of spectral regions and interpretation strategy, see our FTIR interpretation guide or the functional groups reference.

Multi-Modality Peak Identification

SpectralBench now identifies peaks across three major spectroscopy techniques: FTIR, Raman, and UV-Vis. When you upload a spectrum, the tool automatically detects which modality it belongs to based on the spectral range and characteristics, then applies the appropriate reference database — over 80 FTIR functional groups, 60-80 common Raman bands, or 30-40 UV-Vis chromophores.

The co-occurrence rule engine goes beyond individual peak assignments by recognizing patterns of peaks that appear together. For example, if your FTIR spectrum shows both an O-H stretch near 3300 cm⁻¹ and a C-O stretch near 1050 cm⁻¹, the rule engine identifies this combination as characteristic of an alcohol. With 25-30 rules covering common compound classes — alcohols, carboxylic acids, esters, amides, aromatics, and more — the tool provides compound-level identification rather than just individual peak labels.

An interactive interpretation guide walks you through the results, explaining not just what each peak is, but why the assignments were made and how they relate to each other. This makes SpectralBench valuable both as a productivity tool for experienced spectroscopists and as a learning aid for students encountering spectral interpretation for the first time.

Common FTIR Spectral Regions

The reference table below summarizes the major spectral regions used in FTIR peak identification. SpectralBench's full database contains over 80 entries with more detailed sub-ranges, band shape descriptors, and interferent information than this summary. You can also cross-reference your peak assignments against real measured spectra in the reference library.