English (GB)
22
7.7 Chlorine, 0.01 - 6 mg/l Cl
2
7.7.1 Selection
7.7.2 Important notes
1. Vial cleaning:
As many household cleaners (e.g. dishwasher detergent)
contain reducing substances, the subsequent determination of
chlorine may show lower results. To avoid any measurement
errors, only use glassware free of chlorine demand.
Preparation: Put all applicable glassware into sodium
hypochlorite solution (0.1 g/l) for one hour, then rinse all
glassware thoroughly with deionised water.
2. For individual testing of free and total chlorine, the use of
different sets of glassware is recommended.
See EN ISO 7393-2, section 5.3.
3. When preparing the sample, the escape of chlorine gases,
e.g. by pipetting or shaking, must be avoided. The
measurement must take place immediately after taking the
sample.
4. The DPD colour development is carried out at a pH value of
6.2 to 6.5. The reagents therefore contain a buffer for the pH
adjustment. Strong alkaline or acidic water samples must be
adjusted between pH 6 and pH 7 before the reagent is added.
Use 0.5 mol/l sulphuric acid and 1 mol/l sodium hydroxide,
respectively.
5. For concentrations between 6 and 10 mg, the photometer
shows that the measuring range (Overrange) has been
exceeded. Concentrations above 10 mg/l chlorine can lead to
results showing 0 mg/l. In this event, the water sample must
be diluted with water free of chlorine. 10 ml of the diluted
sample should be mixed with the reagent and the
measurement repeated (plausibility test).
6. Turbidity can lead to errors:
The use of the
DPD No. 1
tablet (No
with high calcium ion contents* and/or high conductivity* can
lead to turbidity of the sample and therefore incorrect
measurements. In this event, the reagent tablet
DPD No. 1
high calcium
(No
) should be used as an alternative.
Even if turbidity does occur after the
DPD No. 3
tablet
(No
) has been added, this can be prevented by
using the
DPD No. 1 high calcium
tablet.
*) It is not possible to give exact values, because the
development of turbidity depends on the nature of the
sample.
7. If
"???"
is displayed at a differentiated test result, see section
8.1 Operating messages in the display (error display)
.
8. All oxidising agents in the samples interfere as they react in
the same way as chlorine.
7.7.3 Chlorine, differentiated
7.7.4 Chlorine, free
The following selection is shown in the
display:
for the differentiated determination of free,
combined and total chlorine.
for the determination of free chlorine.
for the determination of total chlorine.
Select the desired determination with the
arrow
keys
and .
Confirm with the
key.
1
0
0
Chlorine
diff
free
total
>> diff
>> free
>> total
>>
1. Fill a clean vial (
∅
24) with 10 ml of the
water sample, close tightly with the cap.
2. Place the vial in the sample chamber
correctly. See fig.
.
3. Press the [Zero] key.
4. Remove the vial from the sample
chamber and empty it, leaving a few
drops in the vial.
5. Add one
DPD No. 1
tablet
(No
) straight from the foil and
crush the tablet using a clean stirring
rod.
6. Add water sample to the 10 ml mark.
7. Close the vial tightly with the cap and
swirl gently several times until the tablet
is dissolved.
8. Place the vial in the sample chamber
correctly. See fig.
.
9. Press the [Test] key.
10. Remove the vial from the sample
chamber.
11. Add one
DPD No. 3
tablet
(No
) straight from the foil to
the same water sample and crush the
tablet using a clean stirring rod.
12. Close the vial tightly with the cap and
swirl gently several times until the tablet
is dissolved.
13. Place the vial correctly in the sample
chamber. See fig.
.
14. Press the [Test] key. Wait for a reaction
period of 2 minutes.
After the reaction period is finished, the
measurement starts automatically.
The result is shown in the display in:
– mg/l free chlorine
– mg/l combined chlorine
– mg/l total chlorine
1. Fill a clean vial (
∅
24) with 10 ml of the
water sample, close tightly with the cap.
2. Place the vial in the sample chamber
correctly. See fig.
.
3. Press the [Zero] key.
4. Remove the vial from the sample
chamber and empty it, leaving a few
drops in the vial.
5. Add one
DPD No. 1
tablet
(No
) straight from the foil and
crush the tablet using a clean stirring
rod.
6. Add water sample to the 10 ml mark.
7. Close the vial tightly with the cap and
swirl gently several times until the tablet
is dissolved.
8. Place the vial correctly in the sample
chamber. See fig.
.
9. Press the [Test] key.
The result is shown in the display in mg/l
free chlorine.
1
0
0
prepare Zero
press ZERO
Zero accepted
prepare T 1
press TEST
∅
24
Countdown
2:00
T 1 accepted
prepare T 2
press TEST
*,** mg/l free Cl
*,** mg/l comb. Cl
*,** mg/l total Cl
1
0
0
prepare Zero
press ZERO
Zero accepted
prepare Test
press TEST
∅
24
Summary of Contents for DIT-M
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