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

Instruction Manual Calcium Electrode
7
3. Place the mid-range solution (1.0X10
-3
M or 10 ppm) in a 150 ml beaker on the magnetic
stirrer and begin stirring. After rinsing the electrodes with distilled water, blot dry, and
immerse the electrode tips in the solution. When the reading has stabilized, record the mV
value.
4.
Place the most concentrated solution (1.0X10
-2
M or 100 ppm) in a 150 ml beaker on the
magnetic stirrer and begin stirring. After rinsing the electrodes in distilled water, blot dry
and immerse the electrode tips in the solution. When 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). A typical calibration curve can be found in Figure 1.
A calibration curve is constructed on semi-logarithmic paper when using a
pH/mV meter in the millivolt mode. The measured electrode potential in mV
(linear axis) is plotted against the standard concentration (log axis). In the linear
region of the curve, only three standards are necessary to determine a calibration
curve. In the non-linear region, additional points must be measured. The direct
measurement procedures given are for the linear portion of the curve. The non-
linear portion of the curve requires the use of low level procedures.
6. To a clean, dry 150 ml beaker, add 100 ml of sample and 2 ml of ISA. Place the beaker on
the magnetic stirrer and begin stirring at a constant rate. Rinse the electrode tips with
distilled water, blot dry, and lower the electrode tips in the solution. When the reading has
stabilized, record the mV reading. Using the calibration curve, determine the sample
concentration.