spectrometers, the most common method of calibrating the wavelength is to use a
bright line spectrum. In the CPL-300, a low-pressure mercury lamp is built into both
the excitation and emission monochromators, and the wavelength is calibrated at the
wavelength of 546.1 nm of a bright emission line. This is done first for the emission
monochromator and then for the excitation monochromator.
A (1S)-(+)-10-ammonium camphorsulfonate aqueous solution is used to calibrate
the CD intensity. The CD value at 290.5 nm for a 0.06% (w/v) aqueous solution
of this substance is known to be +190.4 mdeg for an optical path length of 10 mm,
and this is used for the scale standard for CD measuring instruments [1]. In the
CPL-300, this solution is placed in the sample compartment, and the wavelengths of
both the excitation and emission monochromators are set at 290.5 nm. Since the
difference in the transmitted light intensity for left- and right-handed circularly
polarized light is accurately known, this is used to calibrate the instrument, as
described in detail below.
The CD value for (1S)-(+)-10-ammonium camphorsulfonate aqueous solution is
mentioned above, indicating that absorption of left-handed circularly polarized light
is larger than that of right-handed circularly polarized light, as shown in Eq. (14.1).
This difference of transmitted left- and right-handed polarized light will be the clear
standard of the intensity for CPL spectrometer. When both excitation and emission
wavelengths of CPL spectrometer are then set to 290.5 nm, the sign of the signal is
negative and the intensity is À190.4 mdeg according to Eq. (14.2).
14.5 Measurement Examples
Substrates that show CPL are widely authorized including organic compounds,
metal complexes, fluorescent proteins, and colloidal molecules. The following
sections describe examples involving camphor, camphorquinone, lanthanoid complex, and green fluorescent protein (GFP). Finally, CPL measurements of solid
samples are discussed, since such applications have recently been attracting
attention.
14.5.1 Camphor and Camphorquinone
These compounds have been the subject of CPL measurements for a long time.
Figure 14.7a, b show CD, CPL, absorption, and fluorescence spectra of camphor and
camphorquinone, respectively.
Because there are two carbonyl groups in camphorquinone, compared to just one
in camphor, the structural difference between the ground and excited states for
14 Principles and Applications of Circularly Polarized Luminescence. . .
315
bright line spectrum. In the CPL-300, a low-pressure mercury lamp is built into both
the excitation and emission monochromators, and the wavelength is calibrated at the
wavelength of 546.1 nm of a bright emission line. This is done first for the emission
monochromator and then for the excitation monochromator.
A (1S)-(+)-10-ammonium camphorsulfonate aqueous solution is used to calibrate
the CD intensity. The CD value at 290.5 nm for a 0.06% (w/v) aqueous solution
of this substance is known to be +190.4 mdeg for an optical path length of 10 mm,
and this is used for the scale standard for CD measuring instruments [1]. In the
CPL-300, this solution is placed in the sample compartment, and the wavelengths of
both the excitation and emission monochromators are set at 290.5 nm. Since the
difference in the transmitted light intensity for left- and right-handed circularly
polarized light is accurately known, this is used to calibrate the instrument, as
described in detail below.
The CD value for (1S)-(+)-10-ammonium camphorsulfonate aqueous solution is
mentioned above, indicating that absorption of left-handed circularly polarized light
is larger than that of right-handed circularly polarized light, as shown in Eq. (14.1).
This difference of transmitted left- and right-handed polarized light will be the clear
standard of the intensity for CPL spectrometer. When both excitation and emission
wavelengths of CPL spectrometer are then set to 290.5 nm, the sign of the signal is
negative and the intensity is À190.4 mdeg according to Eq. (14.2).
14.5 Measurement Examples
Substrates that show CPL are widely authorized including organic compounds,
metal complexes, fluorescent proteins, and colloidal molecules. The following
sections describe examples involving camphor, camphorquinone, lanthanoid complex, and green fluorescent protein (GFP). Finally, CPL measurements of solid
samples are discussed, since such applications have recently been attracting
attention.
14.5.1 Camphor and Camphorquinone
These compounds have been the subject of CPL measurements for a long time.
Figure 14.7a, b show CD, CPL, absorption, and fluorescence spectra of camphor and
camphorquinone, respectively.
Because there are two carbonyl groups in camphorquinone, compared to just one
in camphor, the structural difference between the ground and excited states for
14 Principles and Applications of Circularly Polarized Luminescence. . .
315