３１
４.
Operation Method
Display of Water Quality
About TOC
TOC stands for “Total
Organic
Carbon.”
TOC represents contamination of the water by means of the amount of carbon contained in
organics in wate. Of carbon compounds dissolved in water, the TOC value may be used to
represent the total amount of carbon in organic compounds.
For the A4 water specified in JIS, this is 50ppb or less.
（
JIS
K
0557
）
For measurement, the UV oxi direct conductivity measurement methods are used. The UV
oxidation conductivity measurement method consists of measurement of the conductivity before
and after organic decomposition and of calculation of TOC as the decomposition product from the
difference.
TOC units:
[mgC/L]
､
[μgC/L]
､
[ppm]
､
[ppb]
1[mgC/L]
＝
1000[μgC/L]
＝
1[ppm]
＝
1000[ppb]
To obtain the repeatability of analytical result in the experiment, it is essential to use the super
pure water of certain water quality. To check the water quality, it is necessary to control the
water quality by means of “electric conductivity” and “TOC value.”
Item
Water quality standard
（
JIS
K
0557
）
A1
A2
A3
A4
Total organic carbon
（
TOC
）
mgC/l
1 or less
0.5 or less
0.2 or less
0.05 or less
Conductivity mS/m (25
℃
)
0.5 or less
0.1 or less
0.1 or less
0.1 or less
Zinc
μgZn/l
0.5 or less
0.5 or less
0.1 or less
0.1 or less
Silica
μgSiO
2
/l
-
50 or less
5.0 or less
2.5 or less
Chloride ion
μgCl
-
/l
10 or less
2 or less
1 or less
1 or less
Sulfate ion
μgSO
4
2-
/l
10 or less
2 or less
1 or less
1 or less
In the case of WG270 the quality of distilled water stored in the distilled water tank may be
worse than the A4 level quality temporarily because of contact with the atmospheric air.
WG270 is equipped with the function to recover the water quality of such pure water to
the A4 level by means of circulation under ultraviolet ray irradiation and removal of CO2
gas.
It may take hours for the distilled water stored in the tank after initial start of WG270 to
reach the A4 level water quality. Carry out cleaning of the tank inside as follows:
(1) Install and start operation of WG270 system. Keep operation till the tank is filled with
the distilled water.
(2) Discharge the distilled water totally from the outlet of distilled water tank.
(3) Start operation again and keep operation till the tank is filled with the distilled water.
(4) When the tank is full of the distilled water, continue operation without turning OFF
power supply (keep the distilled water circulating). In four or more hours, use the
distilled water. (This step is necessary for initial operation only).
A guideline is as follows. If the specific resistance of distilled water is maintained at 1.2
Ｍ
Ω
・
cm or more for one hour or more continuously, the distilled water with the A4 level or
higher water quality can always be sampled.
If the specific resistance of distilled water is less than 1.
2MΩ
・
cm, continue operation
(keep the distilled water circulating) for approximately four hours or more before sampling
the distilled water.
When the distilled water has been stored for two weeks or more in the tank, drain the
water totally and start operation. Take steps (3) and (4) above before using the distilled
water.