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8 MAINTENANCE
8.1 Chemical Solutions
The reagent and standard solutions described below are required
to maintain the monitor in operation. Where possible, they should
be freshly made and stored in plastic (for example, polythene)
bottles. Typical reagent solution consumption for a continuously
operating monitor is approximately ten litres per month. The
monitor uses 100 to 150 ml of each standard solution each
calibration cycle. Consumption of the standard solution also
depends on the frequency with which this cycle is carried out.
8.1.1 Reagent Solution
0.5 M ammonium acetate + 0.5 M acetic acid
Warning.
•
Concentrated ammonia should only be handled under a
fume hood. It causes burns and is irritating to the eyes,
respiratory system and skin. Wear rubber gloves and eye
protection. In warm weather, pressure increases in the
bulk container of ammonia and the cap must be released
with care.
•
Concentrated (glacial) acetic acid must be handled with
care under a fume hood. It is flammable and causes
burns. Wear rubber gloves and eye protection.
To prepare 10 litres of the reagent, proceed as follows:
a) Carefully add 570 (±5) ml analytical reagent grade glacial
acetic acid (CH
COOH, 1.05 s.g.) to approximately 5 litres of
3
high purity water.
b) To this solution carefully add 275 (±5) ml analytical reagent
grade ammonia solution (NH
✶
Note.
For 0.91 s.g. ammonia solution, use 350 (±5) ml.
c) Mix and dilute to 10 litres with more high purity water. The pH
of this solution should be 4.5 ± 0.2.
✶
Note.
In certain applications, air bubbles from sample degassing
may collect on the electrode membrane. To remove these
bubbles add 50 (±5) ml of 10% 'Brij 35' solution to 10 litres of
reagent. 'Brij 35' (polyoxyethylene lauryl ether, a non-ionic
surfactant) is available as a solid or as a 30% solution from
Merck Ltd.
8.1.2 Reference Electrode Filling Solution
The reference electrode contains a salt bridge solution of 1.0 M
sodium sulphate. Prepare as follows:
a) Dissolve 14.2 (±0.1) g analytical grade anhydrous sodium
sulphate in approximately 80 ml of high purity water.
b) Dilute the solution to 100 ml with more high purity water.
c) Store the solution in a tightly stoppered plastic bottle.
OH, 0.88 s.g.).
4
8.1.3 Standard Solutions
Two standard solutions of known chloride concentration
appropriate to the measuring range are required to calibrate the
monitor. To prepare a stock solution of 10,000 mg l
proceed as follows:
1) Dry approximately 20 grams of analytical reagent grade
sodium chloride at 140°C for four hours.
2) Weigh out 16.48 (±0.01) g of the dried salt; dissolve it in
approximately 400 ml of high purity water and make up to
1 litre in a volumetric flask with more high purity water. This is
a 10,000 mg l
–1
chloride solution.
3) Prepare the standard solution required by accurate dilution of
–1
the 10,000 mg l
stock solution.
8.2 Scheduled Servicing
The following servicing schedule has been produced as a general
guide only. It may be necessary to amend the schedule to suit the
particular installation and sample conditions.
8.2.1 Regular Visual Checks
It is recommended that the monitor and the sampling system is
visually inspected on a regular basis to check the correct
functioning of the system and to assure the integrity of the
readings.
a) Check for leaks, particularly around the sample and drain
pipework connections.
b) Confirm sample flow by checking delivery to the constant
head unit and effluent from the drain.
c) Check liquid flow through sensor flowcell.
d) Check for excessive build-up of air in the flowcell.
e) Check liquid levels in the reagent and standard solution
containers.
f) Check for malfunction indications on the instrument display.
✶
Note. The mains and pump/heater switches are
situated on the right hand side of the User Junction Box.
8.2.2 Four Weekly
a) Inspect all tubing and flowcell for leaks and deterioration.
b) Examine all tubing and flowcell for signs of accumulation of
solid deposits. These tend to accumulate in the reference
electrode compartment of flowcells and may be cleaned to
drain by squirting high purity water from a 'squeezy' bottle into
the de-bubbler vent on top of the flowcell, and the use of small
bottle brush.
c) Clean monitor pipework if necessary.
d) Check the filling solution in the reference electrode and top-up
if necessary.
–1
chloride ions,
29
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