Safe
Water System Manual
ANNEX
C:
HOW TO TEST CONCENTRATION OF FRESHLY-PRODUCED
SODIUM HYPOCHLORITE FOR QUALITY ASSURANCE
Materials
needed:
·
1 ml pipettes
· pipetter (for drawing up solution into the pipette)
·
2 100-ml graduated cylinders
· distilled water
· colorimetric
chlorine comparator (Hach kits, test strips, other colorimeters)
Testing
procedure:
·
Fill both graduated cylinders with 99 ml of distilled water.
· Draw
up 1ml of freshly-prepared sodium hypochlorite and put it in first graduated cylinder,
mix well.
· Draw up 1ml of solution from first graduated cylinder and
put it in second graduated cylinder, and mix well.
· Measure the solution
in the second graduated cylinder in the chlorine comparator-the result will be
measured in mg/liter.
· With this method, the units in mg/liter correspond
exactly to the concentration of the disinfectant produced. (For example, if the
solution from the second graduated cylinder is 0.5 mg/liter, then the sodium hypochlorite
solution is 0.5%.)
Basis
of this calculation:
First
graduated cylinder:
X mg hypochlorite solution/100ml
(99ml H2O + 1ml of hypochlorite solution) = X mg/100ml
Second
graduated cylinder:
Y mg x 1ml of solution from
1st cylinder/100ml (99ml H2O + 1 ml 1st cylinder solution) = Y mg/100ml
Example:
If
the sodium hypochlorite solution is 0.5%, this equals 0.5gm/100ml, which equals
500mg/100ml. In 1ml, there are 5mg.
Therefore,
in the first cylinder, you have:
5mg/100ml
(99ml H2O + 1ml hypochlorite solution)
1ml of this solution has 0.05mg of solution.
In
the second cylinder, you have:
0.05
mg/100ml (99ml H2O + 1 ml solution from first cylinder)
The
concentration of this solution in mg/liter (which is what is measured in the chlorine
comparators) is 0.5 mg/liter. If you get this measurement in the chlorine comparator
after doing this procedure, the sodium hypochlorite solution is 0.5 gm/100ml or
0.5%.
Alternative
Testing Procedure for Sodium Hypochlorite Concentration (if graduated cylinders
are not available)
Materials
needed:
·
1ml pipette
· 1 20 liter container
· distilled water
·
chlorine comparator
Testing
procedure:
·
Fill 20 liter container (attempt to fill exactly; variation by a few ml will not
appreciably affect results).
· Add 2ml of sodium hypochlorite solution
and mix well.
· Measure this solution with chlorine comparator.
·
With this method, the units in mg/liter correspond to the concentration of the
disinfectant produced. (For example, if the solution is 0.5 mg/liter, then the
sodium hypochlorite solution is 0.5%.)
Example:
If
the concentration of the sodium hypochlorite solution is 0.5%, or 0.5gm/100ml,
or 500mg/100ml, in 1ml of solution there are 5 mg.
In
2ml of solution, there are 10mg.
10mg/20
liters = 0.5mg/liter. If you get this measurement in the chlorine comparator after
doing this procedure, the sodium hypochlorite solution is 0.5 gm/100ml or 0.5%.
For
quality assurance of bleach production, a form should be used to monitor each
production run of sodium hypochlorite. The following form is a sample:
Hypochlorite
Production Record
| Date | Operator | Time
machine
turned on | Time
machine
turned off | Salt
(kg) | Water
(liters) | Sodium
hypochlorite
concentration | pH | No.
of
bottles
filled | Comments |
| | | | | | | | | | |
| | | | | | | | | | |
| | | | | | | | | | |
| | | | | | | | | | |
| | | | | | | | | | |
| | | | | | | | | | |
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