Thermo Fisher Scientific Ion Selective Electrodes Chloride - Manual (Page 10)

Instruction Manual Chloride Electrode
Low Level Chloride Determination (using a pH/mV meter)
Use the following low level chloride measurement procedure in the non-linear portion of the
calibration curve. (See Figure 1). This procedure is recommended for solutions containing less than
1.0X10
-4
M.
1.
Using 20 ml of standard ISA, dilute to 100 ml with distilled water. This low level ISA
(1.0M NaNO
3
) is added at the rate of 1 ml low level ISA to each 100 ml of sample. The
background ionic strength will be 1.0X10
-2
M.
2.
Dilute 10 ml of 0.1M standard to 100 ml to prepare a 1.0X10
-2
M standard solution for
measurements in moles per liter. Use the 1,000 ppm standard for measurements in ppm.
Standards should be prepared fresh daily.
3.
Add 1 ml of the low level ISA to a 100 ml volumetric flask and fill to the mark with
distilled water. Pour this solution into a 150 ml beaker and place the beaker on the
magnetic stirrer. Begin stirring at a constant rate.
4.
Place the electrode tips in the solution. Assure that the meter is in the mV mode.
5.
Add increments of the 1.0X10
-2
M or 1,000 ppm standard as given in Table 2 below.
6.
After the reading has stabilized, record the mV reading after each addition.
TABLE 2: Step-wise Calibration for Low Level Chloride Measurements
Added Concentration
Step Pipet Volume (ml) M ppm
1 A 0.1 1.0X10
-5
1.0
2 A 0.1 2.0X10
-5
2.0
3 A 0.2 4.0X10
-5
4.0
4 A 0.2 6.0X10
-5
6.0
5 A 0.4 9.9X10
-5
9.9
6 B 2.0 2.9X10
-4
29.0
7 B 2.0 4.8X10
-4
48.0
Pipet A = 1 ml graduated pipet
Pipet B = 2 ml pipet
Solutions: additions of 1,000 ppm or 1.0X10
-2
M standard to 100 ml
of ISA as prepared in Step 3 above.
7. On a semi-logarithmic graph paper, plot the millivolt reading (linear axis) against the
concentration (log axis) as in Figure 1.
8.
Rinse the electrodes in distilled water and blot dry.
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