25
change in conductivity for each degree change in temperature (%/
°°°°
C), which is called the
temperature coefficient. In extreme cases, the temperature coefficient may have a value as high
as 7%/
°
C. Each conductive ion has a different temperature coefficient.
When practical, control the temperature of the solution to be analyzed. For high precision work
(±1%), maintain the temperature at 25
°
C ± 0.1
°
C. For routine lab work, 25
°
C ± 0.5
°
C may be
acceptable. (Ref: ASTM D1125-82 Standard Methods of Test for Electrical Conductivity of
Water)
When sample temperature control is not practical, use temperature correction to determine the
conductivity at 25
°
C. The temperature coefficient of your sample can be determined either from
published data or from measurements of representative samples. This coefficient may then be
applied to correct future measurements on samples of similar composition. If sample
composition changes appreciably, the coefficient should be redetermined.
Once the temperature coefficient is known, the conductivity at 25
°
C can be manually determined
from the following equation:
where T
= temperature of sample
ℵ
ℵ
ℵ
ℵ
25
= conductivity at 25
°°°°
C
ℵ
ℵ
ℵ
ℵ
T
= conductivity at measurement temperature T
αααα
= temperature coefficient of the conductivity solution
Determining The Temperature Coefficient
You can determine the linear temperature correction coefficient of a solution by measuring its
conductivity at different temperatures using the following equation:
where T
= temperature of sample
ℵ
ℵ
ℵ
ℵ
25
= conductivity at 25
°°°°
C
ℵ
ℵ
ℵ
ℵ
T
= conductivity at measurement temperature T
α
αα
α
= temperature coefficient of the conductivity solution
Small Sample Measurements
It is not always possible to immerse the conductivity cell in a solution for measurements. If the
quantity of solution is not sufficient for a proper measurement with a dip cell, a sample must be
removed for assay. For this application, use the 3254 fill cell. This cell requires 5 mL of sample.
Alternatively, any 3200 or 3400 Series cell, except the 3418 or 3440, may be inverted and used
as a fill cell.
ℵ
ℵ
25
T
=
1 + (T - 25)
α
α
=
-
(T - 25)
T
25
25
ℵ
ℵ
ℵ
