Thermo Fisher Scientific Ion Selective Electrodes Calcium - Manual (Page 9)

Instruction Manual Calcium Electrode
9
1. Dilute 10 ml of the 0.1M standard to 1,000 ml to prepare a 1.0x10
-3
M standard solution
for measurements in moles per liter. Dilute 10 ml of the 1,000 ppm or 1 ml of the 100 ppm
standard to 1,000 ml to prepare a 10 ppm standard solution for measurements in ppm.
2.
Soak the calcium electrode for at least 1 hour in 1.0x10
-3
M or 100 ppm calcium standard
solution.
3.
To a 150 ml beaker, add 100 ml of distilled water. Place the beaker on the magnetic
stirrer and 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
-3
M or 10 ppm standard as given in Table 2 below.
6.
After the reading has stabilized, record the mV reading after each addition.
TABLE 2: Step-wise Calibration for Low Level Calcium Measurements
Added Concentration
Step Pipet Volume (ml) M ppm
1 A 0.1 1.0X10
-6
1.0X10
-2
2 A 0.1 2.0X10
-6
2.0X10
-2
3 A 0.2 4.0X10
-6
4.0X10
-2
4 A 0.2 6.0X10
-6
6.0X10
-2
5 A 0.4 9.9X10
-6
1.0X10
-1
6 B 2 2.9X10
-5
2.9X10
-1
7 B 2 4.8X10
-5
4.8X10
-1
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.
7. On semi-logarithmic graph paper, plot mV reading (linear axis) against the concentration
(log axis) as in Figure 1.
8.
Rinse the electrodes in distilled water and blot dry.
9.
Measure out 100 ml of the sample into a 150 ml beaker and place the beaker on the
magnetic stirrer and 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 1-2
hours by repeating Steps 2-7 above.
Low Level Calcium Determination (using an ion meter)
Follow the procedure given for normal calcium determinations using an ion meter and the blank
correction procedure.
Titration