Eppendorf BioPhotometer plus - Manual (Page 20)

5 Operation
20
BioPhotometer plus — Operating manual
5.5 Proteins
You can measure the protein concentrations directly by measuring in the UV range at 280 nm or
after adding reagent in the VIS range.
5.5.1 Protein 280 nm
The measurements can be evaluated via a factor entered into the parameters or via a single point
calibration (measuring a standard).
• Factor: This evaluation mode is preprogrammed ex factory. However, you still have to enter
the factor before the first measurement.
If you modify the parameter "CUVETTE" (preprogrammed to 10 mm) the modified thickness
of the layer will be taken into account by the device when calculating the results. This means
you do not need to adjust the factor for evaluation but have to provide the input for an optical
path length of 10 mm.
• Standard: Alternatively you can program the evaluation mode "Standard" ("STD") (see
Methods with evaluation via standards on page 21).
Results display
In addition to the concentration result and the absorbance at measuring wavelength 280 nm the
absorbances at 2 additional wavelengths are displayed as an indication for the purity of the
measured protein sample. The absorbance at 340 nm should be near zero for pure samples.
Tubid measuring solutions have raised absorbances at all measuring wavelengths distorting the
measuring result. You can partially correct the distortion by enabling the parameter
"CORRECTION A
340
".
5.5.2 Protein after adding reagent (Bradford, BCA, Lowry)
You can evaluate these methods via factor or calibration (standard measurement).
• Factor: If you evaluate via factor you must take into account when making the entry that the
factor is adjusted to the selected result unit.
If you modify the parameter "CUVETTE" the modified optical path length is, however, taken
into account by the device when calculating the results. This means you do not need to adjust
the factor for evaluation but have to provide the input for an optical path length of 10 mm.
• Standard: For evaluation via calibration you can program up to 10 different standards for
these methods. The procedure for calibration is described in the next chapter (see Methods
with evaluation via standards on page 21).
Top: method name and sample number
Center: result and unit
Bottom right: absorbance results
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