Instruction manual

It is possible to calculate the ratio of ammonia to ammonium ion, theoretically, if the pH is known.
A. Martell and R. Smith in Critical Stability Constants
, Plenum Press, New York, 1974, state:
[NH
4
+
] [NH
4
+
]
⎯⎯⎯⎯ = ⎯⎯⎯⎯ K ~ 10
-9.3
[H
3
O
+
] [NH
3
] 10
-
pH
[NH
3
]
at 25
o
C, X = 0.1 where pH ~ 9.3
The ratio of ammonium to ammonia is given by:
[NH
4
+
]
⎯⎯⎯⎯ = K
-pH
= 10
9.3-pH
[NH
3
]
Both temperature and ionic strength will cause the exact value of K to vary. If, for example, while
the pH at 25
o
C and X = 0.1 is 9.3, an increase in ionic strength to X = 1.0 yields a pH of 9.4, at
25
o
C.
TROUBLESHOOTING GUIDE
The goal of troubleshooting is the isolation of a problem through checking each of the system
components in turn: the meter, the glassware the electrodes, the standard and reagents, the sample,
and the technique.
Meter
The meter is the easiest component to eliminate as a possible cause of error. Most meters are
provided with an instrument check-out procedure in the instruction manual and a shorting strap for
convenience in troubleshooting. Consult the manual for complete instructions and verify that the
instrument operates as indicated and is stable in all steps.