Spectrophotometry
Chapter 2
Basis of Derivative Spectrophotometry
2.1
The Main Law of Light Absorption by a Substance
Photobiological processes occur under the influence of light of ultraviolet (UV), visible, and near infrared spectral regions. Generally, values of light flux intensity, I, and wavelength, l are used in optical measurements. The frequency index n is also considered to characterize an absorbed light. Frequency is expressed in reciprocal seconds [cÀ1] and presents itself as the ratio of a radiation velocity c to a wavelength l [cm or nm]:
¼ c=l ¼ 3Á1017 =lnm ; n where c ¼ 3 Â 1010 cm Á cÀ1 or 3 Â 1017 nm Á cÀ1, the velocity of light. The frequently used index is the wavenumber equal to the number of waves in 1 cm. n The wavenumber is a reciprocal wavelength expressed in reciprocal centimeters:
½cmÀ1 : ¼ 1=lcm ¼ 107 =lnm n Thus, ¼ 40; 000 cmÀ1, when l 250 nm. A number of spectrophotometers have n wavenumbers on the scale dials. For example, the wavelength of the cadmium red
˚
line, as accepted by international agreement, is equal to 6438.4696 A (angstroms).
˚ is 1/6438.4696 part of cadmium red line.
So 1 A
Only absorbed quanta can realize photochemical impact and the reader should remember that a spectral region of a photobiological process is conditioned by the absorption spectrum of a substance involved in this process.
The extinction law for actinic monochromatic light absorbed by a substance layer can be written in the exponential or logarithmic form:
I ¼ I0 Á 10ÀeCd ;
V.S. Saakov et al., Derivative Spectrophotometry and Electron Spin Resonance (ESR)
Spectroscopy for Ecological and Biological Questions,
DOI 10.1007/978-3-7091-1007-2_2, # Springer-Verlag Wien 2013
(2.1)
5
6
2
lgðI0 =IÞ ¼ eCd;
Basis of Derivative Spectrophotometry
(2.2)
where I0 and I are light intensity before and after passing through a layer of substance, of solution, or a leaf, e is a coefficient depending on wavelength
Basis of Derivative Spectrophotometry
2.1
The Main Law of Light Absorption by a Substance
Photobiological processes occur under the influence of light of ultraviolet (UV), visible, and near infrared spectral regions. Generally, values of light flux intensity, I, and wavelength, l are used in optical measurements. The frequency index n is also considered to characterize an absorbed light. Frequency is expressed in reciprocal seconds [cÀ1] and presents itself as the ratio of a radiation velocity c to a wavelength l [cm or nm]:
¼ c=l ¼ 3Á1017 =lnm ; n where c ¼ 3 Â 1010 cm Á cÀ1 or 3 Â 1017 nm Á cÀ1, the velocity of light. The frequently used index is the wavenumber equal to the number of waves in 1 cm. n The wavenumber is a reciprocal wavelength expressed in reciprocal centimeters:
½cmÀ1 : ¼ 1=lcm ¼ 107 =lnm n Thus, ¼ 40; 000 cmÀ1, when l 250 nm. A number of spectrophotometers have n wavenumbers on the scale dials. For example, the wavelength of the cadmium red
˚
line, as accepted by international agreement, is equal to 6438.4696 A (angstroms).
˚ is 1/6438.4696 part of cadmium red line.
So 1 A
Only absorbed quanta can realize photochemical impact and the reader should remember that a spectral region of a photobiological process is conditioned by the absorption spectrum of a substance involved in this process.
The extinction law for actinic monochromatic light absorbed by a substance layer can be written in the exponential or logarithmic form:
I ¼ I0 Á 10ÀeCd ;
V.S. Saakov et al., Derivative Spectrophotometry and Electron Spin Resonance (ESR)
Spectroscopy for Ecological and Biological Questions,
DOI 10.1007/978-3-7091-1007-2_2, # Springer-Verlag Wien 2013
(2.1)
5
6
2
lgðI0 =IÞ ¼ eCd;
Basis of Derivative Spectrophotometry
(2.2)
where I0 and I are light intensity before and after passing through a layer of substance, of solution, or a leaf, e is a coefficient depending on wavelength
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