Thermo Fisher Scientific Ion Selective Electrodes Silver - Manual (Page 13)

Instruction Manual Silver/Silver Sulfide Electrode
13
2. Dilute 1 ml of 0.1M standard to 1 liter to prepare a 1.0X10
-4
M solution for measurements
in moles per liter. Prepare a 10 ppm standard solution by diluting 1 ml of the 1,000 ppm
standard to 100 ml of solution for measurements in ppm. Standards should be prepared
fresh daily.
3.
Add 1 ml of 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
-4
M or 10 ppm silver standard as given in Table 2 below.
6. After the reading has stabilized, record the mV reading.
TABLE 2: Stepwise Calibration for Low Level Silver Measurements
Added Concentration
Step Pipet Volume (ml) ppm M
1 A 0.1 0.01 1.0X10- 7
2 A 0.1 0.02 2.0X10- 7
3 A 0.2 0.04 4.0X10- 7
4 A 0.2 0.06 6.0X10- 7
5 A 0.4 0.10 9.9X10- 7
6 B 2.0 0.29 2.9X10- 6
7 B 2.0 0.48 4.8X10- 6
Pipet A = 1 ml graduated pipet
Pipet B = 2 ml pipet
Solutions: additions of 10 ppm or 1.0X10-
4
M
standard to 100 ml of ISA as prepared in Step 3 above.
7.
On semi-logarithmic graph paper, plot the millivolt reading (linear axis) against the
concentration (log axis) as in Figure 2.
8.
Rinse the electrodes in distilled water and blot dry.
9.
Measure out 100 ml of the sample into a 150 ml beaker, add 1 ml of low level ISA, and
place the beaker on the magnetic stirrer. Begin stirring. Lower the electrode tips into the
solution. After the reading has stabilized, record the mV reading and determine the
concentration from the low level calibration curve.
10. Prepare a new low level calibration curve daily. Check the calibration curve every two
hours by repeating Steps 2-7.
TITRATION
Titration is a very accurate determination of total sulfide or total silver concentration. This method
makes use of the electrode as an endpoint detector. The electrode can also be used to determine
halide concentrations.