Thermo Fisher Scientific CyberScan pH 5000 - Manual (Page 89)

Instruction Manual CyberScan pH5500/ 5000
Direct Reading with Standards
The direct reading method is the most common method of ion
measurement. When using this method, you will use standards of
known values to standardize the meter with ion standards. An ionic
strength adjuster (ISA) is added to both the standards and the
sample. 2 to 5 standards are used to standardize the meter. The
standards should bracket the expected value of the sample. The Ion
specific electrode is immersed in a stirring sample and the ion
concentration is read directly from the meter.
Direct Reading with Blank offset
The blank method is a method commonly used for determination of
ion concentration in a sample with a very low level of ions present.
Because of background interference at low concentration levels, a
blank is used and the value of the ion concentration in the blank is
subtracted from the value of the measured sample.
Known Addition Method
The known addition method is an incremental method used for
samples with a complex matrix. A standard with a known
concentration of the ion species of interest is added to the sample.
The difference in mV potential is then used to calculate the
concentration of the ion of interest.
Known Subtraction Method
The known subtraction method is also an incremental method. The
ion of interest in the sample is not identical to the ion in the standard
solution. The standard of known ion concentration that is added to the
sample quantitatively reacts in the sample with the ion of interest.
This reaction removes a fixed amount of the ion of interest from the
sample solution. The ion concentration is then calculated based upon
the difference in the mV potential.
Analate addition
The analate addition method is a modification of the known addition
method. In the Analate Addition method, the initial mV measurement
is recorded in a standard solution. The ion in the standard solution is
the ion of interest and is detected by the ion selective electrode in
use. A sample containing the ion of interest is then added to the
standard solution. The difference in the mV potential is then used in
the calculation of the concentration of the ion of interest. This method
is useful if the sample temperature is significantly different than that
of the standard. When the small volume of hot sample is added to the
larger volume, the temperature impact becomes negligible.
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