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9 REFERENCE
Each positive and negative ion in the solution will migrate toward the oppositely charged pole.
The result is that current flows through the solution by means of ion conductivity. When this
occurs, resistance R(expressed in ), is in inverse proportion to the area A (expressed in m
of the pole plates, as is the case with metal and other conductors, and is proportional to the
distance l (expressed in m) between the two pole plates. These relationships are expressed
by equation 1, below.
R = r×l/a = rJ (Equation 1)
R: Resistance()
r: Specific resistance(m)
a: Pole plate area(m
l: distance between pole plates(m)
J: Cell constant(m
Specific resistance (expressed in m) is an index that indicates the difficulty with which
current flows and is a constant determined according to the solution. The inverse of r
(expressed in m), which is L (and is equal to 1/r), is called the "specific conductivity" and is
widely used as an index to express the ease with which current flows. Specific conductivity L
is generally referred to as simply "conductivity" and is expressed in units of S/m.
Inserting conductivity L (expressed in S/m) into equation 1 results in equation 2, below.
R = J/L (Equation 2)
As is clear from equation 2, when a conductivity cell having a cell constant J of 1 m
in other words, when a conductivity cell having two pole plates that each have an area A of 1
2
m
and are positioned parallel to each other such that the distance l between the two plates is
1 m is used l the inverse of the resistance R of the solution (expressed in ) between both
pole plates is the conductivity. Conductivity is defined in this way, but it changes according to
the temperature of the solution. The conductivity of a solution is generally expressed as the
value when the solution is 25ºC.
9.8
Evaluating Coefficients
When it is decided that there is an obvious existence of the linear function relationship
between the measured concentration X
value Y
ii=1, 2, cn), the calibration curve (regression expression) is expressed by
i
Y = a + bX
Gradient b and Y-intercept a to the X-axis of this regression line are expressed by the least-
square method using the measurement value as follows:
a = Y
b =
a and b are rounded to one digit larger than the effective digits of the measurement value.
170
2
)
1
)
bX
Σ(X
X)(Y
Y)
i
i
=
2
Σ(X
X)
i
ii=1, 2, cnj and the corresponding manually-analyzed
i
nΣX
Y
(ΣX
)(ΣY
)
i
i
i
i
2
2
nΣX
(ΣX
)
i
i
2
)
1
is used l
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