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3
Good Measurement Practices
General Considerations
A similar effect can occur in cases of incomplete mixing. This is especially
true where the specific gravities or miscibilities of the solvent and analyte
are quite different. Again, stirring is a way to prevent this kind of
problem.
In an unstirred cell, it is sometimes possible to observe local
photodegradation of sensitive analytes. Because the actual volume of the
sample in the light path is very small, stirring the sample will reduce the
time any given analyte molecule is in the light path. This minimizes the
photodegradation and increases homogeneity. Using a flow cell with
continuous flow can yield similar results.
Checklist for Best Results
Cell:
Measurements:
48
Cell is made of quartz or glass
Apertured cells have black sides
Apertured cells have an aperture greater than or equal to 3 mm
Cell windows are free of fingerprints and other contamination
Flow cell used instead of an apertured standard cell
Solution in cell is free of floating particles
Both solution in cell, and cell walls are free of bubbles
Solution in cell is mixed homogeneously
Blank measured on same solvent as sample
Blank measurement shows a flat baseline
show a good and a poor baseline)
Cell orientation of blank and sample measurements is the same
Ideally, the cell is not removed between the measurement, which means
the cell is filled/rinsed using a pipette or a flow cell is used
Time between blank and sample measurement should be short
Agilent Cary 8454 UV-Visible Spectroscopy System Installation Guide
(Figure 11
and
Figure 12
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Troubleshooting
