M silver. at concentrations equal or less than 10 – Hanna Instruments HI 4115 User Manual

Page 7

dards. Add stir bar and mix thoroughly and continu-
ously before taking measurements. A lower level ionic
strength adjuster is prepared by diluting HI 4000-00
ISA (20 mL diluted to 100 mL). This should be used
at a dose of 1 part per 100 parts sample or standard.
Sample ionic strengths will be approximately 10

-2

3) Follow section VII to optimize test set-up.
4) During calibration it is best to start with lower concen-

tration samples first. Wait for a stable measurement
before recording values. Slightly longer equilibra-
tions are required at lower concentrations .

5) To prevent carry over and contamination of samples,

rinse sensors with deionized water and dab dry be-
tween samples.

Typical Linearity for HI 4015 & HI 4115

for Silver Measurement

150

200

250

300

350

400

450

500

-Log of Concentration (M)

Regular Level
Low Level

XI.

XI. Direct Calibration and Measurement

Direct Calibration and Measurement

The direct calibration technique is a simple procedure for
measuring many samples. A direct reading ISE meter (HI
4222 or equivalent) determines concentration of the un-
known by a direct reading after calibrating the meter with
the standards. The meter is calibrated with two or more
freshly made standards that are in the linear measurement
range of the unknowns. Unknowns are read directly. At
very low levels of silver, special precautions must be em-
ployed for reproducible measurements. Water used for
standards must be free of halides and sensors and glass-
ware must be rinsed repeatedly with this water to prevent
carry over. Plastic beakers are recommended. In the region
where the electrode response appears curved, more calibra-
tion points are needed, and calibration will need to be
repeated more frequently. See

“Procedure for Silver” be-

low for additional instructions.
A pH/mV meter in mV mode with semi-log graph paper
may also be used. Two or more freshly prepared standards
that are in the measurement range of the unknowns are
measured in mV mode on the meter.
These values are plotted on the semi-log paper and the
points are connected to form a straight-line curve. When
samples are measured, their mV values are converted to
concentration by following the mV to the concentration axis
on the semi-log plot.

Procedure for Silver
1) Follow sections VIII and IX to prepare sensors for

measurement.

2) Follow section VI to prepare standard solution. Stan-

dards should bracket and fall within the range of
interest.
Two mL HI 4000-00 ISA is added to 100 mL of both
samples and standards for measurements equal or
above 10

-4

M silver. At concentrations equal or less

than 10

-4

M silver, prepare a separate calibration curve

and use 1 mL of a diluted ISA in sample and stan-