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The calculation of the quantities required to prepare Potassium Hydrogen Phthalate (KHP) standard solutions
with various purities are given as an example below:
Name:
Formula:
Carbon, 12
Oxygen, 16
Potassium, 39 x 1
Hydrogen, 1
Total weight
47% of KHP is Carbon. Purity of the KHP is 99.9%. Therefore, to prepare a 1000 mgC/l standard solution,
add 2.13g of KHP in a flask and add enough deionized water to make it exactly 1 liter solution.
Note that the quantities required change with the % purity of the chemical used. Table 8 below gives the KHP
quantities required at various % purity for the preparation of 1000mgC/l calibration standard.
Table 8 Quantity of KHP required to prepare 1000 mgC/l standard at various purities.
% Purity of KHP
100
99.9
99.5
99.0
95.0
90.0
To prepare standard solutions containing more than 1000 mgC/l, the required solvent can be mixed directly
with deionized water. Table 9 below gives the required quantity of KHP for various concentration standard
solutions to be mixed with deionized water and added enough deionized water to make the solution exactly 1
liter.
Table 9 Quantity of KHP required to prepare various concentration TOC standard solutions.
TOC Standard Solution
Concentration (mgC/l)
1000
1250
1500
2000
5000
10000
Potassium Hydrogen Phthalate
C
H
KO
8
5
4
x8
=
96
x4
=
64
=
39
x5
=
5____________
=
204.22 g/mol
to prepare 1000 mgC/l Standard
Quantity of 99.9% KHP (grams)
to be added into 1 Liter DIW
Quantity of KHP (grams)
2.127
2.129
2.138
2.149
2.239
2.364
2.129
2.661
3.194
4.258
10.645
21.290
Page 71
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