10
11
XII.
XII.
XII.
XII.
XII. Other Measurement T
Other Measurement T
Other Measurement T
Other Measurement T
Other Measurement Techniques
echniques
echniques
echniques
echniques
Known Addition (for Na
+
)
An unknown concentration can be determined by adding a
known amount (volume and concentration) of measured
ion to a known volume of the sample. This technique is
called Known Addition. The method can use an ideal
sensor slope, but actual determined slopes at the tempera-
ture of measurement should be used if known. This method
is preprogrammed in the Hanna HI 4222 pH/ISE/mV meter,
which simplifies the method greatly.
Example: Sodium ion determination with known addition.
1. A 50 mL sample of unknown (Vsample) is placed in
a clean plastic beaker with a FC300 sensor. Add 10
mL of ISA HI 4016-00 or HI7090L (V
ISA)
Mix well.
and record the stable mV value. (mV 1)
2. 5 mL (Vstd) of 10
-1
M (Cstd) standard is added to the
beaker and the mV value increases. The unknown
sodium concentration in the original sample
(Csample) can then be determined by the following
equation.
3. The procedure can be repeated with a second stan-
dard addition to verify slope and operation of the
method.
XIII.
XIII.
XIII.
XIII.
XIII.pH
pH
pH
pH
pH
The FC300 electrodes are best used in pH from 9.5 to 14.00.
The ratio of sodium to hydrogen ion should be greater than
10000. For example, if sodium is .05M, Hydrogen ion
must be 0.000005M; 5.30 pH or greater. If sodium is
.00001M, pH must be 7.00 pH. Samples that fall beyond
this range must be adjusted with ISA. See Section VI.
XIV
XIV
XIV
XIV
XIV. Storage
Storage
Storage
Storage
Storage
The FC300 sodium electrodes may be stored in storage
solution or in aqueous sodium solutions with ISA between
sample measurements.
If the electrode will be used frequently and needs to be
ready for use, take measures to prevent evaporation of fill
solution. Top off fill solution, and replace the fill hole cover
and protective cap with a few drops of storage solution over
the sodium sensitive membrane . Store electrode upright.
Before using, rinse off electrode and top off fill solution.
For long term storage, wash all salts from assembly with
deionized water. Replace the fill hole cover and protective
cap with a few drops of storage solution over the sodium
sensitive membrane. Store in shipment box.
C
sample
=
(
V
T
)10
∆
E/S
- (
V
S
’
)
C
standard
V
standard
V
sample
V
S
’
(
V
sample
+
V
standard
+
V
ISA
)=
V
T
(
V
sample
+
V
ISA
)=
V
S
’
XV
XV
XV
XV
XV.
.
.
.
. Conversion T
Conversion T
Conversion T
Conversion T
Conversion Tables
ables
ables
ables
ables
Multiply by
Multiply by
Multiply by
Multiply by
Multiply by
Moles/L (M) Na
+
to ppm Na
+
(mg/L)
22990
ppm Na
+
(mg/L) to M Na
+
(Moles/L)
4.35 X 10
-5
-5
-5
-5
-5
ppm Na
+
(mg/L) to ppm NaCl (mg/L)
2.54197
ppm NaCl (mg/L) to ppm Na
+
(mg/L)
0.39339