Yokogawa PH72 Personal pH/ORP Meter - Manual (Page 74)

IM 12B03D02-01E
9-7
9. Technical Information
Test solution pH
9
0
20
40
60
A
lka
line e
rr
o
r
(mV)
10 11 13 14
F0907.EPS
12
Solution temperature
at 25
؇
C
3mol/l-Na
+
1mol/l-Na
+
0.1mol/l-Na
+
Figure 9.7 Ion Concentration vs Alkaline Error
9.6 The Acid Error
The acid error also varies depending on the glass membrane compositions and the types
of acids. It increases gradually with immersion time and finally reaches equilibrium.
Once a glass electrode has the acid error, it cannot recover soon even by being soaked in
a neutral solution and needs considerable time. Practically, the acid error is small
compared to the alkaline error so that it is negligible.
pH
-1
Acid error (mV)
0
10
30
50
1 3
F0908.EPS
2
Solution temperature
at 25
؇
C
H
2
SO
4
H
3
PO
4
HCl
Figure 9.8 Acid Type vs Acid Error