Single Analate Subtraction - Thermo Scientific Orion Versa Star Pro User Manual

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Chapter 4 pH, pH/ISE and pH/LogR Measurement Modules
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72 Orion Versa Star Pro Meter User Manual

Single Analate Subtraction

In single analate subtraction, the first measurement uses known standard solution containing
the type of ions that the ISE can measure and that will complex with the analate of interest in
the unknown sample. The second measurement follows the addition of the unknown sample
that reduces the concentration of the ions in the measurement solution. The concentration of
the analate in interest in the unknown is then calculated. Concentrations are in Molarity or
Normality due to the stoichiometric nature of the subtraction.
Ensure the subtraction ability of the analate/sample concentration and volume added does not exceed
the concentration of the chosen standard.
A convenient standard volume is 100 mL.
The analate/sample may be added by volume only. A volume of 1 mL usually works.
The standard solution to which additions are made should be approximately 1/50 the expected sample
concentration.
1. Prepare the ion selective electrode (ISE) according to the instructions in the electrode user
manual. Prepare all required solutions (ionic strength adjusters, standards, etc) and review
any special requirements outlined in the electrode user manual. Connect the ISE, and any
other electrodes to be used, to the module inputs on the selected channel.
2. Determine the ISE slope as directed in the electrode user manual.
3. In the measurement mode, press the channel key until the channel with the pH/ISE
module with ISE connected is shown. If needed, press the mode key until ISE
Measurement is shown as the measure mode and use the
Electrode Type.
4. In the measurement mode, press the setup key.
5. Press the ,,  or  key to highlight Channel 1, Channel 2, Channel 3 or Channel 4
and press the f3 (Select) key.
a. Select the appropriate channel number that the ISE is connected.
6. Press the  or key to highlight Incremental Techniques and press the f3 (Select) key.
7. Press the  or  key to highlight Single Analate Subtraction and press the f3 (Select)
key.
8. Press the f3 (Clear) key as needed to delete the displayed slope value. Use the numeric
keypad to enter the ISE slope value determined in step 2 and press the f2 (Accept) key.
9. Enter the standard volume using the numeric keypad and press the f2 (Accept) key.
10. Enter the total volume (standard volume plus added ISA volume) using the numeric keypad
and press the f2 (Accept) key.
11. Enter the standard concentration using the numeric keypad and press the f2 (Accept) key.
Analate Subtraction Recommendations
ISE Mode Menu to set the
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