Attenuated Total Reflectance Mode

• Non-aqueous liquid or solid
• Must cover 2mm² crystal

Grazing Angle Mode

• Extremely thin layers on a reflective substrate
• Substrate 2 x 1.5 cm² or larger

Transmission Mode

• Thin films 1 cm² or larger
• Powder 1-2 mg
• <10µL for liquids
• Must be non-aqueous

A sample is illuminated with infrared light, the absorption of which causes molecular vibrations in the sample. These vibrations are characteristic of functional groups in the sample. A representative spectrum is shown to the left with some of the evident functional groups denoted. FTIR is not able to determine connectivity of functional groups.

FTIR-ATR is capable of rapidly determining the major organic chemical species present in a sample, with a detection limit of 1-5% by weight. FTIR-GA is used for analyzing molecular layers on a reflective surface. FTIR-Transmission can provide a greater signal-to-noise ratio in some cases than attenuated total reflectance.