Hanna Instruments HI 4003 Instruction Manual page 11

Cadmium ion selective electrode

Enlarged version

appear on polishing strip move the paper slightly

and continue polishing.

If the membrane is damaged, the response becomes

extremely sluggish, or the slope of the electrode has

decreased significantly, and procedures above have

not helped, the sensor should be replaced.

XI. XI. XI. XI. XI. 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. The

meter is calibrated with two or more freshly made stan-

dards that are in the linear measurement range of the

unknowns. Two mL of ISA (HI 4000-00) is added to each

100 mL volume of standard or sample. More calibration

standards are required in non-linear regions. Unknowns

are read directly.

Samples with concentration greater than 0.1 M should be

diluted to be within the working range of the electrodes.

The final result must be multiplied by the corresponding

dilution factor to determine the actual concentration.

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.

Hi 4103