Eppendorf BioPhotometer plus - Manual (Page 43)

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11 Evaluation procedure
BioPhotometer plus — Operating manual
11 Evaluation procedure
This chapter describes the available evaluation procedures in the method programs (see
Parameter on page 26) and the calculation of a dilution by the device software.
11.1 Evaluation with factor
C = calculated concentration
A = measured absorbance
F = factor
The factor is programmed in the parameter list and can be modified. For the dye methods the
factor for calculating the dye component is calculated from the absorbance coefficient of the
device.
The factor always relates to the cuvette optical path length of 10 mm. If you change the parameter
CUVETTE the modification is taken into account by the device when calculating the results.
Therefore you do not need to change the factor for the evaluation.
If, on the other hand, you modify the concentration unit, you have to ensure that the factor is
adjusted for the selected unit.
11.2 Evaluation using standards
11.2.1 Single point calibration
F = calculated factor
C
S
= nominal concentration of the standard
A
S
= measured absorbance of the standard
The nominal concentration is programmed in the parameter list and can be modified.
If multiple measurement (2x, 3x) has been programmed for the standard, then the evaluation
from the measured absorbances takes place via linear regression taking into account the zero
value. After calculating the regression a CV value (coefficient of variation with a unit of %) is
formed as measure for the scattering of the measured values. If the CV is greater than 10% it will
be displayed. In this case the calibration will only be stored after confirmation.
The calculation of the sample concentration takes place using the calculated factor:
Hint!
When comparing the measuring results to those of other photometers / spectrometers note that
the values may depend on the bandwidths of the devices. In the following cases the differences
may be significant:
• The absorbance spectrum shows a narrow peak in the measurement wavelength.
• The measurement is carried out not at the maximum but at the edge of a peak.
You should therefore check the accuracy of the method by measuring standards.
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