Thermo Fisher Scientific CyberScan pH 5000 - Manual (Page 141)

Instruction Manual CyberScan pH5500/ 5000
Analate Addition and Analate Subtraction
In the Analate methods, the initial millivolt reading is taken with the
electrode immersed in the standard; then an aliquot of sample is
added, and the final millivolt reading is taken. Sample concentration
is calculated from the change in the millivolt readings.
Analate Addition
V
V
s
s std
+ V
C =
s
C
std
( )
10 UE/S
-
V
std
V
s
( )
Analate Subtraction
V
V
s
s std
+ V
C =
s
C
std
( )
10 UE/S
-
V
std
V
s
( )
As with known addition, with analate addition the sample and the
standard solution contain the same ion being measured. With analate
subtraction, the ion being measured. With analate subtraction, the ion
being measured is in the standard solution, and not in the sample
solution. For example, a fluoride standard and a fluoride ISE might be
used to measure to aluminium concentration of a sample. When the
sample containing aluminium is added to the standard it reduces the
measured fluoride content of the standard. The amount of reduction
is proportional to the aluminium in the sample.
The analate methods offer the same advantages as do the addition
methods in that they effectively deal with complex samples. A distinct
advantage of the analate subtraction method is that it can be used in
cases where an ISE does not exist for a given species, such as
aluminium in the example cited.
Prior to use the electrodes should be conditioned in distilled or
deionized water for at least 10 minutes or in accordance with the
manufacturer’s instructions.
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