25
Calculations for Software
136
Orion AquaMate 7000 Vis and Orion AquaMate 8000 UV-Vis
Thermo Scientific
Linear regression
through zero
A = a
1 *
(c)
Where:
A = absorbance
c = concentration
a
1
= slope
The slope is calculated as:
a
1
= SXY/SXX
This model requires:
• Slope is not equal to zero or infinity
• At least one standard data point with concentration
>0
• The absorbance of the 0 concentration blank = 0A
Segmented model
The segmented model requires:
• Data for at least two standard data points with
different concentrations and absorbances
• Slopes of all segments must be ascending (positive)
or descending (negative)
Validity of standard
curves
A(c
1
) > A(c
2
) for all c
1
> c
2
or
A(c
1
) < A(c
2
) for all c
1
> c
2
Where:
A = absorbance
c
1
, c
2
= concentration
Valid nonlinear standard curve
If this is not the case, there will be more than one
solution within the specified domain, and the message
“Curve cannot be used to determine sample
concentrations – it may produce ambiguous results”
will appear when the curve is viewed.
Invalid nonlinear standard curve
Calculation
Calculation(s)
Graphs
