Thermo Fisher Scientific Ion Selective Electrodes Cyanide - Manual (Page 7)

Instruction Manual Cyanide Electrode
7
NaOH (ISA). After assuring that the meter is in the mV mode, lower the electrode tips into
the solution. After the reading has stabilized, record the mV reading.
3.
Place 100 ml of the mid-range solution in a 150 ml plastic beaker. Place the beaker on the
magnetic stirrer and begin stirring at a constant rate. Add 1 ml of 10M NaOH (ISA). After
rinsing the electrodes with distilled water, blot dry, and lower the electrode tips into the
solution. After the reading has stabilized, record the mV reading.
4.
Place 100 ml of the most concentrated standard solution in a 150 ml plastic beaker. Place
the beaker on the magnetic stirrer and begin stirring at a constant rate. Add 1 ml of 10M
NaOH (ISA). After rinsing the electrodes with distilled water, blot dry, and lower the
electrode tips into the solution. After the reading has stabilized, record the mV reading.
5.
Using the semi-logarithmic graph paper, plot the mV reading (linear axis) against the
concentration (log axis). Extrapolate the curve down to about 1.0X10
-5
M.
6. To a clean, dry, 150 ml plastic beaker, add 100 ml of the sample and 1 ml of 10M NaOH
(ISA). Place the beaker on the magnetic stirrer and begin stirring. Rinse the electrodes with
distilled water, blot dry, and lower the electrode tips into the solution. When the reading
has stabilized, record the mV reading. Using the calibration curve, determine the sample
concentration.
7.
The calibration should be checked every 2 hours. Assuming no change in ambient
temperature, place the electrode tips in the mid-range standard. After the reading has
stabilized, compare it to the original reading recorded in Step 3 above. A reading differing
by more than 0.5 mV or a change in the ambient temperature will necessitate the repetition
of Steps 2-5 above. A new calibration curve should be prepared daily.
Direct Measurement of Cyanide (using an ion meter)
1. By serial dilution of the 1.0X10
-2
M or 1,000 ppm cyanide standard, prepare two standards
whose concentration is near the expected sample concentration. Measure 100 ml of each
standard into individual 150 ml beakers and add 1 ml of 10M NaOH (ISA) 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 cyanide 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. Place the more concentrated solution
on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tips into
the solution.
6.
Adjust the meter to the concentration of the cyanide standard and fix the value in the
memory according to the meter manufacturer's instructions after stabilization of the
reading.