98 Agilent 8453 UV-visible Spectroscopy System Operator’s Manual
4 Using your Agilent 8453 UV-visible Spectroscopy System
When Do I Have to Measure a Blank?
When Do I Have to Measure a Blank?
The measurement data acquired by your spectrophotometer is instrument
independent. To achieve this independency, a reference measurement must be
performed. All consecutive measurements are referring to the last measured
reference.
In the Agilent ChemStation software, the reference measurement is combined
with a baseline measurement. The baseline displayed is information about the
quality of the current reference. In absorbance mode the data should be close
to 0 AU and in transmission mode the data should be close to 100%.
Typically reference measurements for dissolved samples are made on the cell
filled with the solvent used. Here, in addition, the absorbance properties of the
cell and the solvent are influencing the reference data. In wavelength ranges
where your solvent or cell is absorbing, the noise of the baseline spectrum is
high. Reliable sample data cannot be expected in these areas.
Therefore new reference or blank measurements are required when
• you change your measurement cell or its orientation relative to the
measurement position
• you use a different solvent or event a different lot of the same solvent
• the time between your reference measurement and the sample
measurement get too long
• the time conditions are depending on the aging rate of your lamps and
possible changes of your environmental conditions—typically the last blank
measurement should not be older than half an hour.
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