HI5221 User Manual

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Profile - See pH Setup section.

Reading Mode

This option allows the user to select the desired reading mode: Direct, Direct/AutoHold, Known Addi-

tion, Known Subtraction, Analyte Addition and Analyte Subtraction. Four of these Reading Modes are

collectively known as Incremental Methods (see ISE Theory section for details). Direct measurements

and Direct/AutoHold measurements are also available.

Direct

Direct measurements are analogous to taking pH measurements. The ISE is calibrated in ion standards

and sample measurements are made directly. The ISE’s manual should be consulted for tips and prac-

tices of making Direct measurements. The ion concentration can be read directly from the instrument.

Direct/AutoHold

Direct/AutoHold measurements are made similar to Direct measurements. The advantage of using

Direct/AutoHold is a measurement that has not reached equilibrium will not be used. Only after

the chosen stability criteria has been met will the meter go into the Direct/AutoHold mode. Using

Direct/AutoHold removes the subjective nature of stability.

Known Addition

In the Known Addition method, a sample is measured with an ISE before and after the addition of

a known volume of a standard. The mV difference is then used to calculate the concentration of the

ion in the original sample.

Known Subtraction

In the Known Subtraction method, a sample is measured with an ISE before and after the addition

of a known volume of a reactant standard. The reactant standard reacts with the measured ion in

the sample, reducing it’s concentration. The mV difference is then used to calculate the concentration

of the ion in the original sample. The stoichiometric ratio between reactant standard and ion in the

sample must be known.

Analyte Addition

Analyte Addition is similar to the Known Addition method, with the difference being that an aliquot

of sample is added to a known volume of standard. Both solutions contain the same measured ion. The

standard is measured with an ISE before and after the addition of a known volume of a sample. The

ion concentration is then calculated using the difference in mV potential. The sample should increase

the concentration of the ion being measured.

ISE SETUP (HI5222 only)

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User Manual - Page 38