Thermo Fisher Scientific Ion Selective Electrodes Cyanide - Manual (Page 8)

Cyanide Electrode Instruction Manual
8
7.
For low level measurements (below 8X10
-6
M or 0.2 ppm), place the rinsed, dried
electrodes into a solution containing 100 ml of distilled water and 1 ml ISA. After
stabilization, fix the blank value in the meter according to the meter manufacturer's
instruction.
8.
After rinsing the electrodes and blotting dry, place the electrode tips into 100 ml of the
sample and 1 ml of ISA. After stabilization, read the concentration directly from the meter
display.
9.
The calibration should be checked every 2 hours. Assuming no change in ambient
temperature, place the electrode tips in the first cyanide 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 Step
2-10 above. The meter should be re-calibrated daily.
Low-Level Cyanide Measurements (using a pH/mV meter)
Use the following low level cyanide measurement procedure in the non-linear portion of the
calibration curve (below 8X10
-6
M or 0.2 ppm). A more accurate electrode indicator technique, such
as titration, using a silver/sulfide ion electrode, may be preferred below these levels.
1. By serial dilution, prepare 100 ml of 1.0X10
-3
M or 10 ppm cyanide standard from the
1.0X10
-2
M or 1,000 ppm cyanide standard.
2.
Using a 150 ml plastic beaker, add 100 ml of distilled water and 1 ml ISA. Place the
beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode
tips into the solution. Assure that the meter is in the mV mode.
3.
Increments of the standard should be added to the beaker according to the steps
outlined in Table 2 below. After the reading stabilizes, record the mV reading for each
addition.
TABLE 2: Low Level Measurement Calibration Curve
Added Concentration
Step Pipet Volume (ml) ppm M
1 A 0.1 0.01 1.0X10
-6
2 A 0.1 0.02 2.0X10
-6
3 A 0.2 0.04 4.0X10
-6
4 A 0.2 0.06 6.0X10
-6
5 A 0.4 0.10 9.9X10
-6
6 B 2.0 0.29 2.9X10
-5
7 B 2.0 0.48 4.8X10
-5
Pipet A = 1 ml graduated pipet
Pipet B = 2 ml pipet
Solutions: additions of 1.0X10
-3
M or 10 ppm standard to 100 ml
of distilled water and 1 ml ISA