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

Ammonium Electrode Instruction Manual
6
11. Immerse the electrode tip(s) in the solution and wait for the reading to stabilize. Read the
concentration directly from the meter display.
12. The electrodes should be re-calibrated every 1-2 hours. Simply repeat Steps 2-8 (2-9)
above.
Low Level Ammonium Determination (using a standard pH/mV meter)
This procedure is recommended for solutions with ionic strengths less than 1.0 x 10-
2
M. If the
solution is high in ionic strength, but low in ammonium, use the same procedure, but prepare a
calibration solution with a composition similar to the sample.
1. Using 20 ml of stock ISA, dilute to 100 ml with distilled water.
2.
Dilute 1 ml of the 0.1M standard to 100 ml to prepare a 1.0x10-
3
M standard solution for
measurements in moles per liter. Dilute 10 ml of the 1,000 ppm standard to 100 ml to
prepare a 100 ppm standard solution for measurements in ppm.
3.
To a 150 ml beaker, add 100 ml of distilled water and 1 ml of low level ISA. Place the
beaker on the magnetic stirrer and begin stirring at a constant rate.
4.
Place the electrode tip(s) in the solution. Assure that the meter is in the mV mode.
5.
Add increments of the 1.0x10-
3
M or 100 ppm standard as given in Table 2 below.
6.
After the reading has stabilized, record the mV reading after each addition.
TABLE 2: Stepwise Calibration for Low Level Ammonium Measurements
Added Concentration
Step Pipet Volume (ml) M ppm
1 A 0.1 1.0X10-
6
0.1
2 A 0.1 2.0X10-
6
0.2
3 A 0.2 4.0X10-
6
0.4
4 A 0.2 6.0X10-
6
0.6
5 A 0.4 9.9X10-
6
1.0
6 B 2 2.9X10-
5
2.9
7 B 2 4.8X10-
5
4.8
Pipet A = 1 ml graduated pipet
Pipet B = 2 ml pipet
7. On semi-logarithmic graph paper, plot the mV reading (linear axis) against the
concentration (log axis) as in Figure 1.
8.
Rinse the electrode(s) in distilled water and blot dry.