Orion Benchtop pH/ISE Meter Instruction Manual
Special Features
43
Single Known Subtraction Measurement Procedure
In known subtraction, each addition of standard subtracts an increment of
the species to be measured. The known subtraction procedure and meter
prompts are the same as the known addition procedure except that the meter
asks for the reaction ratio. At this prompt enter the correct reaction ratio of
the species to be measured with the standard to be added. For example:
A sulfide (S
=
) sample is to be subtracted by the addition of silver (Ag
+
).
Two Ag
+
ions are required to subtract each S
=
ion, therefore the reaction
ratio is 0.5.
NOTE: Make sure the correct reaction ratio of
sample to standard is entered.
Total concentration of the sample should be approximately halved upon
addition of the standard. Therefore sample concentration should be known
within an order of magnitude.
See the following table to choose the correct standard concentration and
volume of addition.
Milliliters of standard Standard should be
to be added per 100 X times expected sample
mL of sample concentration
1 mL 50X
5 mL 10X
10 mL 5X
Select 2-SUBTR for the known subtraction procedure then follow the
meter prompts.
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