Ionode IJ pH V5.1 - Manual (Page 14)

Ionode IJ Instruction Manual 14
calibration. It can also be accurately measured
using the mV mode of a pH meter.
1) Measure the temperature of two buffers and
select the pH values for the buffers at this
temperature (see
Table 2 : pH Values of
Standard Buffers at Various
Temperatures)
2) Measure the mV readings for the two
buffers. Allow several minutes for the
electrode to attain thermal equilibrium with
the buffers.
3) Divide the measured difference by the
theoretical difference (see Table 1 ) and
multiply by 100.
Example:
Buffer 1 (pH 6.865 @ 25ºC): +11 (mV)
Buffer 2 (pH 4.008 @ 25ºC): +174 (mV)
SLOPE(T=25ºC): 59.157 (mV/pH)
 
 
% 4 . 96 100
157 . 59 008 . 4 865 . 6
11 174
Slope %
 
 


Note that ATC provided by pH meters only
corrects the temperature term in the Nernst
equation. It does not correct the temperature
coefficients of buffers unless they are specified
and the meter software calculates accordingly.
With the exceptions of fully dissociated strong
acids and bases, all samples have temperature
coefficients as well. These vary depending on
the nature of the sample and cannot be
corrected by the pH meter. For best reporting,
the temperature at which the measurement has
been made should be stated.
Inbuilt temperature compensation is offered as
an
option for models IJ44 and
IJ64.Temperature sensor types include Pt1000
RTDs, and 10K and 30K NTC thermistors. For