Metrohm 780 - Stored Buffer Series

9.2 Evaluation
140
780/781 pH/Ion Meter, Manual
The calculation of the calibration data depends on the number of pH
buffers used:
1-Point calibration
Slope: The theoretical slope value of 100.0% is used.
pH(0) =
N
1
1
USlope
U
pH
⋅−
−
2-Point calibration
Slope =
( )
( )
N12
12
U
1
pHpH
UU
−
⋅
−
−
pH(0) =
N
USlope
U
pH
⋅−
−
;
pH
,
U
= mean value
3- and more point calibration
With at least 3 calibration buffers a compensation curve according to
the principles of the smallest mean-square error (linear regression) will
be calculated.
Slope =
( ) ( )
( )
N
i
2
i
i
ii
U
1
pHpH
UUpHpH
−
⋅
−
−⋅−
∑
∑
pH(0) =
N
U
Slope
U
pH
⋅
−
−
Variance =
( )
2n
UU
i
2
calculated,ii
−
−
∑
;n = no. of measuring points