Navigator 500
Sodium analyzer
8 Maintenance
OI/ASO550–EN Rev. G
59
8 Maintenance
8.1 Chemical solutions
The reagents and calibration solutions detailed in this section
are required to keep the wet-section operating. Solutions should
be stored in plastic bottles and, where possible, should be
freshly made.
8.1.1 Reagent solutions
Two alternative reagent solutions may be used, depending on
the required lower limit of measurement. Concentrated
ammonia solution, that provides adjustment of sample pH to a
minimum of 10.7 (if fresh 35 % w/v ammonia solution is used) is
suitable for measurements of sodium ion to approximately 0.5
µg kg
-1
. At concentrations below this, hydrogen ion interference
becomes significant and a reagent of di-isopropylamine (DIPA)
should be used. This adjusts the sample pH between 11.2 and
11.5 and enables measurements to be made down to 0.1 µg
kg
-1
.
1. Concentrated ammonia solution – 1 liter (0.22 US gal.).
A 35 % w/v solution (s.g. 0.88) is recommended, but
lower concentrations, to a minimum of 30 % w/v (s.g.
0.89), can be used.
2. Di-isopropylamine – 1 liter (0.22 US gal.).
8.1.2 Standard solutions
The following instructions refer to the preparation of 100 µg l
-1
and 1 mg l
-1
sodium, STANDARD SOLUTION 1 (LOW) and 2
(HIGH) respectively. Alternative concentrations can be prepared
within the measuring range selected by appropriate dilution of
the stock solution.
It is not advisable to prepare static sodium solutions of less than
50 µg l
-1
because low concentration solutions rapidly become
contaminated and change in concentration.
Although the HIGH and LOW standard solutions are typically
one decade apart in sodium concentration, any concentration
difference can be used if the HIGH solution is at least five times
the concentration of the LOW solution. It is necessary to have a
significant change in electrode output to achieve an accurate
calibration.
For all practical purposes, ‘µg l-1’ can be considered equal to
‘µg kg
-1
’ (‘ppb’) and ‘mg l
-1
’ equal to ‘mg kg
-1
’ (‘ppm’).
To prepare stock solution (1000 mg l
-1
sodium ions):
1. Dissolve 2.543 (±0.001) g of analytical reagent grade
sodium chloride in approximately 100 ml high purity water.
Transfer this solution to a one liter volumetric flask and
make up to the one liter mark with more high purity water
to give a stock solution of 1000 mg l
-1
sodium ions. Store
in a plastic container.
2. Pipette 10 ml of this solution to a one liter volumetric flask.
Make up to the one liter mark with high purity water to give
a solution of 10 mg l
-1
sodium ions.
3. Pipette 10 ml of the 10 mg l
-1
solution into a one liter
volumetric flask and make up to the one liter mark with
high purity water to give the LOW standard solution of
100 µg l
-1
sodium ions. Transfer this solution to the bottle
labelled STANDARD SOLUTION 1 (LOW).
4. Transfer 100 ml of the 10 mg l
-1
solution to a one liter
volumetric flask and make up to the mark with high purity
water to give the HIGH standard solution of 1 mg l
-1
sodium ions. Transfer this solution to the bottle labelled
STANDARD SOLUTION 2 (HIGH).
8.1.3 Salt bridge solution
This solution is required for refilling the double junction silver /
silver chloride reference electrode at extended intervals. The
solution supplied with the electrode (3.5 M potassium chloride)
should be used for refilling using the plastic pipette provided.
Warning.
This reagent must 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.
Warning.
DIPA is an extremely inflammable and
irritating colorless liquid with an ammoniacal odor.
Handle with care at all times.
The following points must also be noted:
Avoid breathing vapor and avoid contact with
skin and eyes.
Work under a fume hood, wearing rubber
gloves and eye protection.
Keep away from sources of ignition.
No smoking
In the event of a fire, extinguish with water spray,
foam, dry powder or carbon dioxide.
If a spillage occurs, shut off all possible sources
of ignition and instruct others to keep at a safe
distance. Mop up spillage with plenty of water,
diluting greatly. Ventilate the area well to
evaporate any remaining liquid and dispel vapor.
Effluent from the wet-section contains DIPA (if
this reagent is used). Contact with it should also
be avoided.
Note.
High purity water = water containing less than
2 µg l
-1
sodium ions and a specific conductivity of less than
approximately 0.2 µS cm
-1
.
