Hanna Instruments HI 4521 - Manual (Page 55)

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Make sure the instrument has been calibrated before taking ISE measurements.
When using one of the incremental methods for measurement and no or only a one-point ISE calibration was
performed, a warning message will be displayed on the LCD, notifying the user that at least a two-point ISE
calibration must be performed.
For accurate measurements, add the appropriate
ISAB (Ionic Strength Adjustment Buffer) to both samples and
standards, if necessary. If ISAB is added to the calibration standards, it is important to add ISAB also to the
samples to be measured.
DIRECT MEASUREMENT
To measure the concentration of a sample using the Direct
reading mode:
• Press and then to select ISE Measure mode.
• Select the Direct reading mode (see ISE Setup for details).
• Add ISAB to the sample solution.
• Submerge the Ion Selective Electrode tip and the tempera-
ture probe approximately 4 cm (1½”) into the sample to
be tested. Allow time for the electrode to stabilize.
• The measured concentration value will be displayed on the LCD
in the selected units.
Note: If the reading is out of range, “-----” will be dis-
played on the LCD.
DIRECT/AUTOHOLD MEASUREMENT
To measure the concentration of a sample using the Direct /
AutoHold reading mode:
• Press and then to select ISE Measure mode
for the selected channel.
• Select the Direct/AutoHold reading mode (see ISE Setup for
details).
• Add ISAB to the sample solution.
• Submerge the Ion Selective Electrode tip and the tempera-
ture probe approximately 4 cm (1½”) into the sample to
be tested. Allow time for the electrode to stabilize.
I S E M E A S U R E M E N T I S E M E A S U R E M E N T I S E M E A S U R E M E N T I S E M E A S U R E M E N T I S E M E A S U R E M E N T
(HI 4522 only) (HI 4522 only) (HI 4522 only) (HI 4522 only) (HI 4522 only)
62
Example 1
You have sulfide samples and you are adding Ag
+ . The reaction is:
One mole sulfide sample reacts with 2 moles silver standard (f = ½).
Example 2
You have sulfide samples and you are adding Pb
2+ . The reaction is:
One mole sulfide sample reacts with 1 mole lead standard (f = 1).
Analyte Addition and Analyte Subtraction
Analyte Addition and Subtraction are variations of the previous two methods.
With Analyte Addition, sample (analyte) is added to an ion standard being measured. The standard and
sample contain the same ion. mV are taken before and after the sample addition. From the mV the analyte
concentration is determined.
With Analyte Subtraction, sample (analyte) is added to an ion standard being measured. The analyte reacts
with the measured ion in a known manner thus removing measured ions from the solution. From the change
in mV the concentration of the analyte is determined.
∆
E - the difference of potential from the electrode;
S - the electrode slope, determined in a
previous calibration;
f
- the stoichiometric ratio between sample
and standard;
where: C
SAMPLE
- the sample concentration;
C
STD
- the standard concentration;
V
SAMPLE
- the sample volume;
V
STD
- the standard volume;
and V
T
= V
SAMPLE
+ V
STD