Ionode IJ pH V5.1 User Manual

Page 14

Ionode IJ Instruction Manual

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

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)









100

157

008

865

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