Gas Chromatography - Tandem Techniques - The Combination of the Gas Chromatograph with Other Spectroscopic Systems > Spectroscopy Techniques > Page 13



Where (h) is Planks Constant (i.e., 6.62 x 10-27 erg-sec.)


It follows, that as, nl = c, then,




It is seen from equations (2) and (3) that the energy released on the adsorption of a photon of energy increases linearly with the frequency and inversely as the wavelength of the electromagnetic wave. It also follows, that electromagnetic waves of different frequency will be absorbed by different parts of the physical structure of an adsorbing material and, consequently, could provide information about the physical make up of the substance. Thus, the information obtained from the absorption of an electromagnetic wave will depend solely on its frequency or wavelength. A diagram representing the electromagnetic spectrum is shown in figure 9. To explain figure 9 in more detail, 1 ? is 10-8 cm, 1 nm = 10-7 cm and 1 mm is 10-4 cm. Thus, the wavelength ranges of interest to the chemist or analyst are from about 180 nm to 700 nm (180 nm to 400 nm being designated as the ultra violet region and 400 nm to 700 nm the visible light region), 2 mm to 40 mm the infra red region and 40 mm to 400 mm the far infra red region. In practice, only the UV region (180 nm to 400 nm) and the infra red region (2 mm to 40 mm) are used to any extent in GC spectroscopic combinations.



Figure 9. The Electromagnetic Spectrum