Ionode IJ pH V5.1 - Manual (Page 36)

Ionode IJ Instruction Manual 36
5.4. Calibration Standards
Light's solution and ZoBell's solution are NBS
standards which are stable for several months if
stored in a dark plastic bottle in the refrigerator.
The quinhydrone standards are highly unstable.
They must be made fresh and discarded after
use.
Light's Solution
39.21g ferrous ammonium sulphate,
Fe(NH
4
)
2
(SO
4
)
2
·6H
2
O
48.22g ferric ammonium sulphate,
Fe(NH
4
)(SO
4
)
2
·12H
2
O
56.2mL sulphuric acid (sp. gr. 1.84)
made to 1L with distilled water
Table 7:
Light’s Solution (Ref: Ag/AgCl
Saturated KCl)
Temperature (ºC) Potential (mV)
25 476
ZoBell's Solution
1.408g potassium ferrocyanide,
K
4
Fe(CN)
6
·3H
2
O
1.098g potassium ferricyanide, K
3
Fe(CN)
6
7.456g potassium chloride, KCl
made to 1L with distilled water
Note:
ZoBell’s solution is more stable prepared
in two parts, which are accurately combined 1:1
just prior to use.
Part 1: 1.408g potassium ferrocyanide plus
7.456g of potassium chloride made up to
500mL.
Part 2: 1.098g potassium ferricyanide made up
to 500mL.