Jasco J-1100 - Principles of LD Operation

2
Thus, the ratio between I
A
and S can be approximated with a sufficiently high accuracy for
practical applications.
If E
A
and E
S
represent the output voltages of photomultiplier tube corresponding to light
intensities I
A
and S, respectively, then S/I
A
= E
S
/E
A
. By substituting this expression into
equation (6), it can be expressed as follows:
 








= e
E
E
LC
A
S
e 10
log10log
4500


. (1-7)
If E
S
can be amplified independently of E
A
, equation (7) can be expressed as follows.
 






















=
G
e
E
GE
LC
A
S
e
10
log
10log
4500


, (1-8)
where G represents the amplification factor of E
S
. Since the value E
S
G can be brought very
close to the value of E
A
by choosing an appropriate value for G, [] can be determined with a
high degree of accuracy.
1.1.2 Principles of LD operation
LD (Linear Dichroism) is a phenomenon that the absorption of light differs depending on the
direction of polarization, which is observed with an oriented film and others. Given that I
⊥
is
the energy of vertically polarized transmitted light and I
∥
the energy of horizontally polarized
transmitted light, LD is defined by the following formula.
)/(log
||10||
IIODODLD
⊥⊥
=−
(2-1)
The light from the light source is monochromated and turned into linearly polarized light by the
double-prism monochromator that also functions as a polarizer. The linearly polarized light
from the monochromator is modulated into horizontal and vertical polarized lights by the
modulator. And the light that has transmitted the sample is converted into an electrical signal
by the photomultiplier tube. The component of (I
⊥
+ I
∥
)/2 is always maintained constant by the
photomultiplier cathode voltage. The component of (I
⊥
- I
∥
) is amplified and recorded. The
signal of (I
⊥
+ I
∥
)/2 corresponds to the DC component and that of (I
⊥
- I
∥
) corresponds to the
AC component at 100kHz. LD can be expressed by the following formula using AC and DC
signals.
LD
AC DC
AC DC
=
+
−
log
( / )
( / )
10
1 2
1 2
(2-2)
If AC<<DC, LD can be approximated by the following formula.
LD AC DC e
ap
= ( / )log
10
(2-3)
The error will be 1% or more if LD is 0.2△OD or more. Here, LD can be corrected by the
following formula.
LD
LD e
LD e
cor
ap
ap
=
+
−
log
( ) / (log )
( ) / (log )
1 2
1 2
10
10
(2-4)
ε(LD) is defined by the following formula.
 ( ) /LD LD cl=
(2-5)
where
c
: Concentration(mol/l)
l
: Cell length(cm)