25
I
A130/131
Known Subtraction
The procedure for known subtraction is similar to the known addition
method. The difference is that the standard solution does not contain
the same ionic species that you are trying to measure in the sample.
Instead, it contains an ion that will complex or precipitate the ion of
interest, removing it from the sample.
3.1 Press the
Mode
key and the
key to select the
Ion (Known
Subtraction)
, press the
Enter
key to confirm.
3.2 Repeat steps 2.2 through 2.7 above until the meter shows the
known subtraction result.
Sample Addition
This method is similar to the known addition method, except that the
sample is added to the standard solution.
4.1 Press the
Mode
key and the
key to select the
Ion (Sample
Addition)
, press the
Enter
key to confirm.
4.2 Press the
key to select the electrode type (e.g., Ion 1). Press
the
Enter
key, the meter begins to measure the first mV value,
the icon E1 appears on the screen.
4.3 Rinse the ion selective electrode with distilled water, place the
electrode (and temperature probe) into the sample solution. Wait
for the measurement to stabilize.
4.4 When the reading is stable, press the
Enter
key, the meter begins
to measure the second mV value, the icon E2 appears on the
screen.
4.5 Add a known volume of sample to the standard solution and wait
for the measurement to stabilize.
4.6 When the reading is stable, press the
Enter
key, the screen shows
a parameter list and waits for entering the sample volume,
standard volume and standard concentration (ppm or mg/L).
4.7 Press the
/
key to enter the value, press the
Enter
key to
confirm. When the setting is completed, the meter will calculate
and show the sample addition result.
4.8 Press the
ESC
key to take a measurement again.
Sample Subtraction
This method is similar to the known subtraction method, except that
the sample is added to the standard solution.
5.1 Press the
Mode
key and the
key to select the
Ion (Sample
Subtraction)
, press the
Enter
key to confirm.
5.2 Repeat steps 4.2 through 4.7 above until the meter shows the
sample subtraction result.
Electrode Maintenance
•
Rinse the ion selective electrode thoroughly with distilled water
after use, wipe clean with a lint-free tissue, then replace
protective cap and store the electrode in a dry and cool area.
•
Never scratch the ion sensitive membrane on the bottom of the
electrode.
•
If the electrode response becomes sluggish, soak the electrode
in standard solution for at least 1 hour.
Appendix
Preparation of Ion Standard Solution (1000 ppm)
1.1 Half fill a 1 liter volumetric flask with distilled water and add the
analytical grade reagent according to the instructions in table
below.
Ion Type
Reagent
Weight
Ammonium
NH
4
Cl
2.97 g
Bromide
NaBr
1.29 g
Cadmium
Cd(NO
3
)
2
•
4H
2
O
2.74 g
Calcium
CaCl
2
•
2(H
2
O)
3.67 g
Chloride
NaCl
1.65 g
Cupric
Cu(NO
3
)
2
•
3H
2
O
3.80 g
Cyanide
NaCN
1.88 g
Fluoride
NaF
2.21 g
Iodide
NaI
1.18 g
Lead
Pb(NO
3
)
2
1.60 g
Nitrate
NaNO
3
1.37 g
Potassium
KCl
1.91 g
Silver
AgNO
3
1.57 g
Sodium
NaCl
2.54 g
Sulfide
Na
2
S
•
9H
2
O
7.49 g
Ammonia
NH
4
Cl
3.15 g
1.2 Swirl the volumetric flask gently to dissolve the reagent and fill
to the mark with distilled water.
1.3 Cap and upend the volumetric flask several times to mix the
solution.
Ion sensitive membrane
1L
