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...8 MAINTENANCE
8.3 Shutdown Procedure
8.3.1 Short Term
The nitrate ion–selective electrode may be stored dry or
immersed in a dilute nitrate solution, e.g. 100 mg l
use. It must not be left in the monitor flowcell. Rinse the tip
thoroughly with de–ionised water immediately on removal.
Remember to maintain the ion exchange liquid level 5 mm above
the body seal – see Section 8.2.7 (s).
The reference electrode may be stored in de–ionised water or the
correct salt bridge solution (1 M sodium sulphate) for short
periods. Ensure that the electrode cannot dry out; failure to
observe this results in a blocked ceramic junction, causing
considerable delay when restarting the monitor.
8.3.2 Long Term
For periods longer than one month, the nitrate electrode should
be completely dismantled, rinsed out and returned to the box in
which it was supplied. Proceed as follows:
a) Withdraw the inner electrode, wipe the tip with a tissue and
wash out the gelled filling solution with distilled water. Allow to
air dry and refit the protective rubber teat.
Warning.
• Wear protective gloves and perform the following steps
under a fume hood. Avoid skin contact with the ion
exchanger solution; if contact occurs, wash off
immediately with soapy water.
• Methanol is highly flammable. Avoid contact with skin and
eyes. Do not inhale the vapour.
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b) Hold the electrode body over a small beaker of methanol;
unscrew the end cap and allow the end cap assembly and
ion–exchanger solution to fall into the methanol.
c) Wash the end cap and washer in more methanol; allow to air
dry. Discard the membrane.
d) Wash the electrode body, inside and out, with methanol and
allow to air dry.
The reference electrode is stored with its ceramic junction
covered by a protective teat filled with salt bridge solution. Fit the
fill hole stopper in the salt bridge solution refill aperture.
8.4 Unscheduled Servicing
The monitor indicates abnormal operation by means of signals on
the 20 character dot matrix display and l.e.d's. The indications are
listed in Table 8.1.
8.4.1 Malfunction of the Monitor
It should always be remembered that any unpredictable
problems may be due to the standard or reagent solutions, or their
flow through the flowcell. If any doubts exist regarding the integrity
of the solutions, they should be replaced with freshly prepared
solutions in the early stages of the fault finding investigations.
Note. The accuracy of the monitor is governed by the
condition of these solutions which may be incorrectly made
or contaminated.
In general, any problems are likely to be due to the electrodes,
which may require refurbishment (see Section 8.4.3), but may be
due to other parts of the liquid handling section of the monitor.
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