Fourier-transform infrared (FT-IR) spectroscopy identifies the polar covalent bonds in a material by measuring which infrared frequencies it absorbs. Different functional groups — O-H, C=O, C-H, N-H, and others — vibrate at characteristic frequencies, producing a unique absorption fingerprint for each compound. This survey of common household and laboratory materials uses the FT-IR spectrometer in ATR mode to capture each sample’s spectrum across the mid-infrared range (~550–4000 cm⁻¹), building a reference library of spectra and identifying characteristic functional group signatures in everyday substances.
| Category | Details |
|---|---|
| Instrument | Thermo Scientific Nicolet iS5 FT-IR Spectrometer |
| Mode | Attenuated Total Reflectance (ATR) |
| Range | ~550–4000 cm⁻¹ |
| Resolution | ~7,150 data points per spectrum |
| Runs | Two sessions (19 + 6 samples) |
A background spectrum was collected first to establish a baseline. Each sample was placed directly on the ATR crystal, a spectrum acquired across the mid-IR range, and the raw CSV exported from the instrument software.
| # | Category | Samples |
|---|---|---|
| 1 | Solvents | acetone, isopropanol, water |
| 2 | Food/minerals | coffee, salt, sugar |
| 3 | Personal care | soap, shampoo, conditioner, lotion, sunscreen, cleaner |
| 4 | Polymers | plastic bag, plastic cap, plastic glove, plastic wrapper |
| 5 | Paper | paper, paper-plastic cup |
| 6 | Biological | finger, leaf, orange peel |
| 7 | Control | background |
Raw spectra are available as CSV files each containing two columns (wavenumber in cm⁻¹ and transmittance in %) with ~7,150 data points per spectrum. Data is organized into two experimental runs: ONE (19 samples) and TWO (6 samples) over two different days.
The instrument (Nicolet iS5) applies background correction automatically — each sample’s transmittance is already measured relative to the background spectrum, so non-absorbing regions read ~100% transmittance. The data cleaning pipeline:
Acetone shows a textbook IR spectrum. The dominant peak at ~1,715 cm⁻¹ is the C=O carbonyl stretch — the strongest and most characteristic absorption in ketones. The C–H methyl stretches appear around 2,950–3,000 cm⁻¹, the peaks at ~1,350–1,450 cm⁻¹ are C–H bending (symmetric and asymmetric scissoring of the CH₃ groups), and the sharp peaks in the 1,000–1,300 cm⁻¹ region correspond to C–O and C–C skeletal stretches. The absence of a broad O–H band confirms the sample is anhydrous.
Water produces the classic broad O–H stretching band centered around 3,300 cm⁻¹, spanning nearly the entire 3,000–3,600 cm⁻¹ region due to hydrogen bonding. The sharp peak at ~1,640 cm⁻¹ is the O–H bending (scissoring) mode. The strong absorption rising below 1,000 cm⁻¹ is the librational (rocking) mode of liquid water.
Salt (NaCl) is an ionic compound with no covalent bonds, so it produces a nearly flat baseline with no characteristic IR absorptions. The small features visible are likely surface moisture (trace O–H) and atmospheric CO₂ interference. This makes salt an effective negative control and explains why NaCl is traditionally used for IR sample windows.
Polyethylene (plastic bag) shows an almost pure C–H spectrum. The sharp doublet at ~2,920 and ~2,850 cm⁻¹ corresponds to asymmetric and symmetric C–H stretching of the CH₂ backbone. The C–H bending peaks at ~1,460 cm⁻¹ (scissoring) and ~720 cm⁻¹ (rocking) complete the picture. No O–H, C=O, or other heteroatom peaks — just carbon and hydrogen.
Sugar (sucrose) shows a broad O–H stretching band at 3,000–3,500 cm⁻¹ from its many hydroxyl groups, plus a rich fingerprint region below 1,500 cm⁻¹ dominated by C–O stretching vibrations of the glycosidic bond and sugar ring. The complexity of the fingerprint region reflects the molecule's size — each sugar has a unique IR fingerprint that can be used for identification.
See the static notebook or run the reproducible analysis yourself.