3.8 GOOD PRACTICE GUIDELINES
1.
For optimum performance blank and sample calibration should be carried out at the beginning
and end of every sample batch.
2.
To ensure accurate results are obtained the sample area lid should be kept in the closed position
during measurement.
3.
The styrene cuvettes supplied with the unit are disposable (i.e. ideally they should be used
once and then thrown away). Some repeat use is possible providing extreme care is taken
during cleaning to ensure no damage occurs to the polished surface.
NOTE:
The plastic cuvettes supplied with the unit are not suitable for use below a
wavelength of 310nm.
Other grades of UV plastic cuvettes can be used down to 275nm. If the unit is
being used below this wavelength, UV grade quartz glass cuvettes must be used.
4.
UV quartz glass cells should be used for measurements below 310nm.
5.
Plastic cuvettes are not suitable for use with organic solvents.
6.
Glassware used in the preparation of standards should be made of a high grade borosilicate
glass. The use of soda glass should be avoided wherever possible as leaching can occur during
prolonged contact, giving erroneous results.
7.
Glass cuvettes should be thoroughly cleaned after use. Discard when scratches become evident
in polished surfaces.
8.
Chemical reagents should, wherever possible, be of high grade quality. Contamination can
cause problems, even at very low levels. Diluents (i.e. water or solvents) must be free from
impurities.
9.
There are some substances which do not follow Beer’s Law. When attempting a new method it
is advised that linearity checks should be performed over the range of concentrations being
used. This can be carried out by preparing a quantity of known strength solutions and checking
the results.
a)
Deviations from Beer’s Law may occur at high concentrations by association of
molecular ionic species.
b)
Deviations from Beer’s Law may occur at low concentrations by variation in hydration,
introducing changes in the nature of complex ions.
c)
Absorption which does not obey Beer’s Law will require a graph of known standards
to be plotted. This should indicate Reading vs Concentration. The reading obtained
from the unknowns can then be related to the concentration from the graph.
10.
Samples and standards can “outgas” when left in the cuvette. Bubbles formed on the cuvette
walls will cause reading errors.
11.
When entering the SPECTRUM mode it is recommended that a baseline scan should be carried
out.
640 050/REV B/11-99
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