Chapter
4
|
pH, pH/ISE and pH/LogR Measurement Modules
17.
The meter will display the calculated sample concentration and summary of the incremental
technique performed. Press the
f1 (Esc) key to proceed to the measurement mode or press
the
f2 (Next) key to perform another analysis.
Double Known Addition
Double Known Addition Recommendations
The sample volume should be 100 mL.
The concentration of the standard should be 100 times the expected sample concentration.
The volume of the first addition should be 1 mL and the volume of the second addition should be 10 mL.
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.
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 measurement mode and use the
ISE Mode Menu
to set the Electrode Type.
3.
In the measurement mode, press the
setup key.
4.
Press the ◄ or ► key to highlight the channel setup menu that the ISE is connected with
(Channel 1, Channel 2, Channel 3 or Channel 4)
and press the f3 (Select) key.
5.
Press the ◄ or ►key to highlight Incremental Techniques and press the
f3 (Select) key.
6.
Press the
▲ or
▼ key to highlight Double Known Addition and press the
f3 (Select) key.
7.
Enter the sample volume using the
numeric keypad and press the f2 (Accept) key.
8.
Enter the total volume (sample volume plus added ISA volume) using the numeric keypad
and press the
f2 (Accept) key.
9.
Enter the standard concentration using the numeric keypad and press the
f2 (Accept) key.
10.
Rinse the ISE and any other electrodes in use with distilled water or rinse solution required
for that electrode. Blot the electrode dry with a lint-free tissue or shake the electrode, place
into the prepared sample and press the
f2 (Next) key.
a.
Follow all electrode rinsing and drying instructions or exceptions in the ISE user
manual. Do not wipe or rub the sensing element of the electrode.
11.
Wait for the mV value on the meter to stabilize and press the
f2 (Accept) key.
12.
Enter the first standard volume using the numeric keypad and press the
f2 (Accept) key.
13.
Add the first specified volume of the standard to the sample and press the
f2 (Yes) key.
14.
Wait for the mV value on the meter to stabilize and press the
f2 (Accept) key.
15.
Enter the second standard volume using the numeric keypad and press the
f2 (Accept) key.
16.
Add the second specified volume of the standard to the sample and press the
f2 (Yes) key.
17.
Wait for the mV value on the meter to stabilize and press the
f2 (Accept) key.
50
|
Orion V
ERSA
S
TAR
Meter User Manual
Thermo Scientific
Chapter
4
|
pH, pH/ISE and pH/LogR Measurement Modules
18.
The meter will display the calculated sample concentration and summary of the incremental
technique performed. Press the
f1 (Esc) key to proceed to the measurement mode or press
the
f2 (Next) key to perform another analysis.
Single Known Subtraction
In
known subtraction, each addition of standard subtracts an increment of the species to be
measured. Enter the reaction ratio of the measured species to the added standard. For
example, if a sulfide (S
2-
) sample will 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 in Molarity or Normality should be known within an order of magnitude
and the total sample concentration should be approximately halved upon addition of the
standard. Concentrations are in Molarity or Normality due to the stoichiometric nature of the
subtraction. 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 (in Molarity or Normality)
compared to expected sample concentration
1 mL
50
times more concentrated
5 mL
10 times more concentrated
10 mL
5 times more concentrated
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 measurement mode and use the
ISE Mode Menu
to set the Electrode Type.
4.
In the measurement mode, press the
setup key.
5.
Press the ◄ or ► key to highlight the channel setup menu that the ISE is connected with
(Channel 1, Channel 2, Channel 3 or Channel 4) and press the
f3 (Select) key.
6.
Press the ◄ or ►key to highlight Incremental Techniques and press the
f3 (Select) key.
7.
Press the
▲ or
▼ key to highlight Single Known 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 sample volume using the numeric keypad and press the
f2 (Accept) key.
10.
Enter the total volume (sample volume plus added ISA volume) using the numeric keypad
and press the
f2 (Accept) key.
11.
Enter the standard concentration in Molarity or Normality using the numeric keypad and
press the
f2 (Accept) key.
Thermo Scientific
Orion V
ERSA
S
TAR
Meter User Manual
|
51