24
1st Cal. Point
Two options are available for the 1st Cal. Point parameter: Point and
Offset.
Point:
A new buffer can be added to an existing calibration. The
electrode slope will be reevaluated with the addition of this buffer
(normal operation).
Offset:
The new buffer calibration point can create a constant
offset to all existing pH calibration data (existing calibration
must have a minimum of two pH buffers).
To set the 1st Cal. Point:
• Press
while in
pH Measure
mode.
• Press
.
• Use
or
to select the Calibration option.
• Press
and use
or
to highlight the 1st Cal. Point option.
• Press
/
as desired.
• Press
to return to previous menu.
Edit Custom Buffers
If special custom pH buffers are required during calibration, the
Edit Custom Buffers option is available. Up to five pH custom
buffers can be added. If a custom buffer is used, the user must
verify it’s value at temperature of calibration.
To edit/set the Custom Buffers:
• Press
while in
pH Measure
mode.
• Press
.
• Use
or
to select the Calibration option.
• Press
and use
or
to highlight the Edit
Custom Buffers option.
• For a previous set value, press
to set the custom buffer value to “
----
” if desired and confirm the
setting by pressing
, otherwise press
to edit the selected custom buffer.
• While in edit custom buffer menu press
to set the custom buffer value to 7.000 pH and then use
or
to set the desired custom buffer value.
57
For a positively charged Ion (i.e. Calcium), the reactant addition should decrease the mV. For a
negatively charged Ion (i.e. Sulfide, Fluoride, Chloride), the reactant addition should increase the mV.
Start with a small trial. For example: Measure 50 mL of sample, add a magnetic stir bar, place on a
stirrer, add ISA (consult ISE manual) and place ISE electrode tip in to the sample. Put instrument in mV
mode and record the observed mV. Using a micropipet, add a volume of the Reactant standard. Start by
adding 500 µL at a time (for example). Watch the change in mV. When you have observed
approximately a 15 mV change from the original sample, calculate the total volume added. Adjust
sample and standard volumes proportionally to standard volumes that can be measured with accuracy.
Use volumetric pipettes for standard, ISA and reagent addition.
• Press
then edit the procedure variables to the volumes determined in the prior step.
Procedure:
• Press
to enter Known Subtraction mode.
• Volumetrically add sample to a clean beaker. Add stir bar and place on a magnetic stir plate. Stir
sample. The method will prompt user to add ISA. Place ISE sensor tip into the solution and a mV value
will show on the display.
• Press
to take the first mV reading.
• When the reading is stable, press
to store the first mV reading. The second step of the method
will be displayed on the LCD in which the user is notified to add the Volume of Reagent to the sample.
• Press
to take the second mV reading.
• When the reading is stable, press
to store the second mV reading. The ISE measurement results
will be displayed on the LCD.
• Press
to log the current results into an ISE Method Report. Press
to return to
ISE
Measure
mode. Press
to start another measurement. Rinse ISE sensor between samples.
• Press
, to modify parameters.
Note
: Press
at any time to stop the measurement and return to
ISE Measure
mode.
ANALYTE ADDITION
To measure the concentration of a sample using Analyte Addition method:
• Press
and then
to select
ISE Measure
mode for the selected channel.
• Select the Analyte Addition method (see ISE Setup
→
Reading Mode).
• Prior to starting an AA procedure, the ISE sensor must be calibrated with a minimum of two standards
containing ISA. The slope of the electrode will be used in all calculations involved in AA.
• If following an established procedure: Press
then edit the method variables and follow the
procedure below.
