FTIR Spectroscopy Applications

FTIR spectroscopy is used across a wide range of scientific and industrial disciplines where chemical identification is needed. The technique works with a range of instrument configurations and sampling methods. Here are five major application areas; the polymer section includes an example spectrum.

Pharmaceutical Quality Control

FTIR is indispensable in pharmaceutical manufacturing for verifying raw material identity, monitoring production processes, and performing quality control on finished products. Pharmacopoeial methods (USP <197>, Ph. Eur. 2.2.24) specify infrared spectroscopy as a primary identification technique.

Key uses

  • Raw material identification — incoming inspection of APIs and excipients
  • Polymorphism studies — different crystal forms often show distinguishable FTIR differences, though some differ only subtly
  • Counterfeit detection — comparing suspect samples against authenticated reference spectra
  • Stability testing — monitoring chemical degradation over time

Polymer Identification

Every polymer produces a characteristic FTIR spectrum determined by its molecular backbone and functional groups. FTIR is a standard method for identifying unknown plastics, characterizing copolymers, and monitoring polymerization reactions.

Key uses

  • Plastic identification for recycling — identifying PE, PP, PET, PVC, PS by their spectra (handheld or benchtop ATR-FTIR; automated sorting lines mostly use near-IR)
  • Additive analysis — identifying plasticizers, stabilizers, and fillers
  • Degradation monitoring — tracking oxidation (carbonyl growth), hydrolysis, or UV damage
  • Quality control — verifying polymer grade and batch consistency

Example spectrum: Polystyrene

50010001500200025003000350000.10.20.30.4Wavenumber (cm⁻¹)Absorption index (k)

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Plotted as the absorption index k (the imaginary part of the refractive index), derived from FTIR measurements at the Pacific Northwest National Laboratory. Band positions match an absorbance spectrum of polystyrene; bands at high wavenumber look weaker than they would in absorbance.

Food Science

FTIR enables rapid, non-destructive analysis of food composition and quality. ATR-FTIR in particular requires minimal sample preparation and can analyze solids, liquids, and pastes directly.

Key uses

  • Adulteration detection — identifying additions of cheaper oils, sugars, or fillers
  • Nutritional analysis — quantifying fat, protein, and carbohydrate content
  • Authentication — verifying origin of olive oil, honey, or wine
  • Shelf life monitoring — tracking lipid oxidation and protein denaturation

Environmental Analysis

FTIR is widely used in environmental monitoring for identifying pollutants, analyzing soil and sediment composition, and studying atmospheric chemistry. Its ability to measure gases makes it valuable for emission monitoring.

Key uses

  • Microplastic identification — characterizing polymer type of particles extracted from water, soil, or biota
  • Soil organic matter analysis — quantifying organic carbon and mineral composition using DRIFTS
  • Emission monitoring — measuring stack gas composition (SO₂, NOₓ, CO, CO₂) using gas-cell FTIR
  • Water quality — identifying organic contaminants extracted from surface and groundwater (water itself absorbs strongly in the mid-IR)

Forensic Science

Forensic laboratories use FTIR to analyze trace evidence including fibers, paint chips, drugs, and unknown substances. FTIR microscopy enables analysis of samples as small as 10 μm.

Key uses

  • Fiber identification — determining polymer type and comparing to known reference samples
  • Paint analysis — identifying binder, pigment, and additive composition in automotive and architectural paints
  • Drug identification — rapid screening and identification of seized substances
  • Document examination — analyzing inks, toners, and paper coatings

Frequently Asked Questions

What is FTIR spectroscopy used for?

FTIR spectroscopy is used for chemical identification and analysis across many fields: pharmaceutical quality control, polymer identification and recycling, food adulteration detection, environmental monitoring (microplastics, emissions), forensic analysis (fibers, paints, drugs), semiconductor manufacturing, and art conservation.

Can FTIR identify unknown substances?

Yes, FTIR is one of the primary techniques for identifying unknown substances. By comparing the measured spectrum against a library of reference spectra, the compound can often be identified with high confidence. This is used routinely in pharmaceutical incoming inspection, forensic analysis, and hazmat response.

Is FTIR spectroscopy quantitative?

Yes. According to the Beer-Lambert law, absorbance is directly proportional to concentration and pathlength. Quantitative FTIR requires calibration with known standards and careful attention to sample preparation to ensure reproducible pathlength and consistent sampling conditions.

References

  1. Smith, B. C. Fundamentals of Fourier Transform Infrared Spectroscopy, 2nd ed. CRC Press, 2011.
  2. Silverstein, R. M.; Webster, F. X.; Kiemle, D. J.; Bryce, D. L. Spectrometric Identification of Organic Compounds, 8th ed. Wiley, 2014.