Hanna Instruments HI 4014 - Manual (Page 7)

12 13
5. Hold inner stem and unscrew module and replace
with a new one. (HI 4114-51).
6. Reassemble electrode (see section VII), and refill with
electrolyte. Soak new membrane in potassium solu-
tion to condition before calibration.
2) Follow section VII; General Guidelines to optimize test
set-up.
3) During calibration it is best to start with lower concen-
tration samples first. Wait for a stable reading before
reading/ recording values. Permit longer equilibra-
tion at these levels (3 or 4 minutes).
4) To prevent carry over and contamination of samples,
rinse sensors with deionized water and dab dry be-
tween samples. Do not rub membrane.
Typical HI 4014 and HI 4114 Linearity
-160
-110
-60
-10
40
90
1 2 3 4 5 6
-Log of Concentration
m
V
XI XI XI XI XI. Direct Calibration and Measurement Direct Calibration and Measurement Direct Calibration and Measurement Direct Calibration and Measurement Direct Calibration and Measurement
This method is a simple procedure for measuring many
samples. A direct reading ISE meter (HI 4222 or equiva-
lent) determines concentration of the unknown by a direct
reading after calibrating the meter with the standards. HI
4014-00 ISE is added to both samples and standards to
adjust the ionic strength of the solutions at a dose of 2 mL
per 100 mL standard or sample. The meter is calibrated
with freshly made standards that are in the measurement
range of the unknowns. Unknowns are then read directly.
In the non-linear region, more calibration standards are
required and more frequent calibrations are advised.
A pH/mV meter in mV mode and semi log graph paper
may also be used. Two or more freshly prepared standards
that are in the measurement range of the unknowns (with
ISA added), are measured in mV mode on the meter.
These values are plotted on semi-log paper and the points
are connected to form a straight-line curve. When samples
are measured, their mV values are converted to concentra-
tion by following the mV to the concentration axis on the
semi-log plot.
Procedure:
Follow sections VIII and IX to prepare electrodes for mea-
surement.
1) Follow section VI to prepare standards/ solution. Stan-
dards should bracket and fall within the range of
interest. Standards and solutions should be at the
same temperature.
2 mL of HI 4014-00 is added to 100 mL of
both samples and standards. Add stir bar and mix
before taking measurements.