Thermo Fisher Scientific Ion Selective Electrodes Silver - Manual (Page 12)

Silver/Silver Sulfide Electrode Instruction Manual
12
standard into individual 150 ml beakers and add 25 ml of SAOB and 25 ml of distilled
water to each.
2.
Place the more dilute solution on the magnetic stirrer and begin stirring at a constant rate.
Assure that the meter is in the concentration mode.
3. Lower the electrode tips into the solution.
4.
Adjust the meter to the concentration of the sulfide standard and fix the value in the
memory according to the meter manufacturer's instructions after stabilization of the
reading.
5.
Rinse the electrodes with distilled water and blot dry.
6.
Place the more concentrated solution on the magnetic stirrer and begin stirring at a
constant rate.
7.
Lower the electrode tips into the solution.
8.
Adjust the meter to the concentration of the sulfide standard and fix the value in the
memory according to the meter manufacturer's instructions after stabilization of the
reading.
9.
For low level measurements, place the rinsed, dried electrodes into the solution containing
50 ml of SAOB and 50 ml of distilled water. After stabilization, fix the blank value in the
meter according to the meter manufacturer's instructions.
10. Place 50 ml of the sample, 25 ml of SAOB, and 25 ml of distilled water in a 150 ml
beaker, place it on the magnetic stirrer, and begin stirring.
11.
Immerse the electrode tips in the solution and wait for the reading to stabilize. Read the
concentration directly from the meter display.
12. The calibration should be checked every two hours. Assuming no change in ambient
temperature, place the electrode tips in the first sulfide standard. After the reading has
stabilized, compare it to the original reading in Step 4 above. A reading differing by more
than 0.5 mV or a change in the ambient temperature will necessitate the repetition of Steps
2-8 (9) above. The meter should be re-calibrated daily.
Low Level Silver Determinations (using a pH/mV meter)
This procedure is recommended for solutions with ionic strengths less than 1.0X10
-2
M. If the
solution is high in ionic strength, but low in silver, use the same procedure, but prepare a calibration
solution with a composition similar to the samples.
1. Using 1 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.