In OES spectrometry, atoms in a solid sample are excited by absorption of energy from an electrical source and emit their characteristic electromagnetic radiation in the form of light. The light is focussed by a lens on to a primary slit through which it passes on to a diffraction grating in the spectrometer, where it is separated into line wavelength spectra. Light from selected element lines is isolated by secondary slits and focussed on to photomultiplier tubes. The intensity of a spectral line can by correlated with the concentration of the element producing it.
FTIR spectroscopy exploits the fact that molecules absorb specific frequencies that are characteristic of their molecular structure. A spectrum is recorded by passing a beam of IR light through the sample. Examination of the transmitted light reveals how much energy was absorbed at each wavelength. Using a Fourier transformation instrument enables the measurement of all wavelengths simultaneously. A transmittance or absorbance spectrum is produced, showing at which IR wavelengths the sample absorbs. Each material will have a characteristic 'fingerprint' spectrum.