Supplement I to the Japanese Pharmacopoeia Fourteenth Edition

1374 General Tests, Processes and Apparatus
Supplement I, JP XIV
contained in the apparatus.
Conductivity measurement is generally performed by using
an immersion-type cell. A pair of platinum electrodes,
the surfaces of which are coated with platinum black, is ˆxed
in parallel. Both electrodes are generally protected by a glass
tube to prevent physical shocks.
When the surface area of the electrode is A (cm 2 ), and the
separation distance of the two electrodes is l (cm), the cell
constant C (cm -1 ) is given by the following equation.
C = a・(l/A )
a is a dimensionless numerical coe‹cient, and it is characteristic
of the cell design.
In addition to the immersion-type cell, there are ‰owthrough-type
and insert-in-pipe-type cells. These cells are set
or inserted in an appropriate position in the ‰ow system for
monitoring the quality of water continuously or intermittently,
during the preparation of highly puriˆed water.
Standard Solution of Potassium Chloride
After pulverizing an appropriate amount of potassium
chloride for conductivity measurement, dry it at 500 – 6009C
for 4 hours. Take an indicated amount of the dried potassium
chloride, as shown in Table 1, dissolve it in distilled or
puriˆed water (conductivity less than 2 mS・cm -1 ), previously
boiled and cooled, and adjust to make 1000.0 g, for
preparation of the standard solutions. The conductivity and
the resistivity of the respective standard solutions at 209C
are indicated in Table 1. These standard solutions should be
kept in tightly closed polyethylene or hard glass bottles.
Table 1. Conductivity and Resistivity of the Standard
Solutions of Potassium Chloride at 209C
Concentration
(g/1000.0 g)
Conductivity k
(mS・cm -1 )
Resistivity r
(Q・cm)
0.7455 1330 752
0.0746 133.0 7519
0.0149 26.6 37594
When measurement at 209C cannotbedone,theindicated
value of conductivity for the respective standard solution
(Table 1), can be corrected by using the equation below.
However, the equation is valid only within the range of 20 ±
59C.
k T = k 20 [1 + 0.021(T - 20)]
T: Measuring temperature speciˆed in the monograph
k T : Calculated conductivity of the KCl standard solution
at T9C
k 20 : Conductivity of the KCl standard solution at 209C
Operating Procedure
(1) Cell Constant
An appropriate conductivity cell should be chosen according
to the expected conductivity of the sample solution. The
higher the expected conductivity, the larger the cell constant
required for the conductivity cell, so that the electrical
resistance is within the measuring range of the apparatus
being used. Conductivity cells with a cell constant of the order
of 0.1 cm -1 ,1cm -1 ,or10cm -1 , are generally used.
For determination or conˆrmation of the cell constant, an
appropriate KCl standard solution should be chosen and
prepared, taking account of the expected conductivity of the
sample solution to be measured. Rinse the cell several times
with distilled water. Next, after rinsing the cell 2 – 3 times
withthestandardsolutionusedforthecellconstantdetermination,
immerse the cell in the standard solution contained
in a measuring vessel. After conˆrming that the temperature
of the standard solution is maintained at 20 ± 0.19C orat
the temperature speciˆed in the monograph, measure the
resistance R KCl or the conductance G KCl of the standard solution,
and calculate the cell constant C (cm -1 )byuseofthe
following equation.
C = R KCl ・k KCl or C = k KCl /G KCl
R KCl : Measured resistance (MQ)
G KCl : Measured conductance (mS)
k KCl : Conductivity of the standard solution being used
(mS・cm -1 )
The measured cell constant should be consistent with the
given value within 5z. Ifitisnotconsistent,coattheelectrodes
with platinum black again, or replace the cell with a
new one.
(2) Suitability Test for the Apparatus
Using an appropriate KCl standard solution according to
the expected conductivity of the sample solution, perform
the suitability test for the apparatus. Rinse the conductivity
cell several times with distilled water, and rinse again 2 – 3
times with the selected standard solution. Fill the standard
solution in the measuring vessel. After conˆrming that the
temperature of the measuring system is maintained at 20 ±
0.19C, measure the conductivity of the standard solution.
When this measuring procedure is repeated several times, the
average conductivity should be consistent with an indicated
value in Table 1 within 5z. Further, the relative standard
deviation should be less than 2z.
(3) Measurement
After conˆrmation of the suitability of the apparatus, perform
the conductivity measurement for the sample solution.
Unless otherwise speciˆed, the preparation method for sample
solution should be as speciˆed in the respective monograph.
Rinse the conductivity cell several times with distilled
water, and rinse again 2 – 3 times with sample solution. Immerse
the cell in the sample solution placed in a measuring
vessel. If necessary, agitate gently the sample solution. After
conˆrming that the temperature of the sample solution is
maintained at 20 ± 0.19C or at the temperature speciˆed in
the monograph, measure the resistance R T (MQ) or conductance
G T (mS) of the sample solution, and calculate the conductivity
k T by using the following equation.
k T = CG T or k T = C/R T
Items such as the sample preparation method, the necessity
of blank correction, the calculation method, the speciˆcation
value, and the measuring temperature should be described
in the monograph, if necessary.