Section 6
|
Incremental Techniques
Single Known Subtraction
In known subtraction, each addition of standard subtracts an increment of the species to be
measured. Enter the correct reaction ratio of the species to be measured with the standard to
be added. For example, a sulfide (S
-2
) sample is to be subtracted by the addition of silver (Ag
+
).
Two silver ions are required to subtract each sulfide ion and the reaction ratio is 0.5.
Sample concentration should be known within an order of magnitude and the total sample
concentration should be approximately halved upon addition of the standard. Refer to the
following table to choose the correct standard concentration and volume of addition.
Amount of standard to be added
per 100 mL of sample
Standard concentration compared to expected sample concentration
1 mL
50 times more concentrated
5 mL
10 times more concentrated
10 mL
5 times more concentrated
•
Refer to the appropriate electrode user guide for instructions for preparing the electrode,
required solutions (ionic strength adjusters, standards, etc) and any special requirements.
Determine the electrode slope as directed in the electrode user guide.
•
Ensure that the electrode, ATC probe and reference electrode (if applicable) are connected
to the meter inputs that correspond with the selected channel.
Single Known Subtraction Procedure
1. Prepare the sample as directed in the electrode user guide.
2. In the measurement mode, press the setup key. Press the ▲ / ▼ keys to highlight
Incremental Techniques and press the f2 (select) key.
3. Dual channel display only: Press the ▲ / ▼ keys to select the channel to perform the single
known subtraction on and press the f2 (accept) key.
4. Press the ▲ / ▼ keys to highlight Single Known Subtraction and press the f2 (select) key.
5. Use the numeric keypad, decimal key and +/- key to enter the electrode slope and press the
f2 (accept) key. Determine the electrode slope as directed in the electrode user guide or use
the theoretical slope from the table in the
Electrode ID and Slope for Incremental
Techniques
section.
6. Use the numeric keypad and decimal key to enter the sample volume, in mL, and press the
f2 (accept) key.
7. Use the numeric keypad and decimal key to enter the total volume, in mL, and press the
f2 (accept) key. The total volume includes the sample volume, ISA volume and diluting
agent volume, but not the standard volume.
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Orion Dual Star pH/ISE Benchtop Meter User Manual
Thermo Scientific
Incremental Techniques
|
Section 6
8. Use the numeric keypad and decimal key to enter the concentration of the standard and
press the f2 (accept) key.
9. Use the numeric keypad and decimal key to enter the reaction ratio of sample to standard
and press the f2 (accept) key. For example, if a sulfide (S
-2
) sample is to be subtracted by
the addition of silver (Ag
+
), two silver ions are required to subtract each sulfide ion and the
reaction ratio is 0.5.
10. Rinse the electrode (ATC probe, stirrer probe and reference electrode, if applicable) with
distilled water, blot dry with a lint-free tissue and place the electrode(s) into the sample.
When the electrode and sample are ready, press the f2 (next) key.
11. Wait for the reading to stabilize. When the reading is stable, press the f2 (yes) key.
12. Use the numeric keypad and decimal key to enter the volume of the standard, in mL, to be
added to the sample and press the f2 (accept) key.
13. Add the standard to the sample and press the f2 (yes) key.
14. Wait for the reading to stabilize. When the reading is stable, press the f2 (yes) key.
15. The meter will display the result of the single known subtraction. Press the f3 (log/print) key
to save and end the single known subtraction, export the data to the data log and export the
data to a printer or computer, if a printer or computer is connected to the meter and enabled
in the setup menu.
Note: Press the f1 (escape) key to return to the measurement mode without saving the single
known subtraction.
16. Press the f2 (next) key.
17. To perform a single known subtraction using the values that were entered for the previous
single known subtraction, press the f2 (yes) key. To perform a single known subtraction and
enter new values, press the f3 (no) key. To end the incremental technique and return to the
measurement mode, press the f1 (escape) key.
Thermo Scientific
Orion Dual Star pH/ISE Benchtop Meter User Manual
|
57
Section 6
|
Incremental Techniques
Double Known Subtraction
•
Ensure that the subtraction ability of the chosen standard concentration and volume added
does not exceed the concentration of sample.
o For most double known subtraction analysis, it is recommended that:
o The sample volume should be 100 mL.
o The concentration of the standard added should be 50 times the expected sample
concentration.
•
The volume of the first addition of standard should be 1 mL and the volume of the second
addition of standard should be 10 mL.
•
Refer to the appropriate electrode user guide for instructions for preparing the electrode,
required solutions (ionic strength adjusters, standards, etc) and any special requirements.
•
Ensure that the electrode, ATC probe and reference electrode (if applicable) are connected
to the meter inputs that correspond with the selected channel.
Double Known Subtraction Procedure
1. Prepare the sample as directed in the electrode user guide.
2. In the measurement mode, press the setup key. Press the ▲ / ▼ keys to highlight
Incremental Techniques and press the f2 (select) key.
3. Dual channel display only: Press the ▲ / ▼ keys to select the channel to perform the
double known subtraction on and press the f2 (accept) key.
4. Press the ▲ / ▼ keys to highlight Double Known Subtraction and press the f2 (select) key.
5. Use the numeric keypad and decimal key to enter the sample volume, in mL, and press the
f2 (accept) key.
6. Use the numeric keypad and decimal key to enter the total volume, in mL, and press the
f2 (accept) key. The total volume includes the sample volume, ISA volume and diluting
agent volume, but not the standard volume.
7. Use the numeric keypad and decimal key to enter the concentration of the standard and
press the f2 (accept) key.
8. Use the numeric keypad and decimal key to enter the reaction ratio of sample to standard
and press the f2 (accept) key. For example, if a sulfide (S
-2
) sample is to be subtracted by
the addition of silver (Ag
+
), two silver ions are required to subtract each sulfide ion and the
reaction ratio is 0.5.
9. Rinse the electrode (ATC probe, stirrer probe and reference electrode, if applicable) with
distilled water, blot dry with a lint-free tissue and place the electrode(s) into the sample.
When the electrode and sample are ready, press the f2 (next) key.
58
|
Orion Dual Star pH/ISE Benchtop Meter User Manual
Thermo Scientific
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