110 Agilent Cary 8454 UV-Visible Spectroscopy System Operator’s Manual
5 Using your 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 independence, a reference measurement must be
performed. All consecutive measurements refer 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. The absorbance properties of the cell and the
solvent also influence 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.
To ensure the highest accuracy of sample measurement, the blank
measurement should be taken immediately prior to the actual sample
measurement.
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