Jenway 7305 - Manual (Page 14)

The optical layout of the 7300 and 7305 spectrophotometers is shown below:
Figure 3.2.1 – Diagram of light path
The light from the pre-focused tungsten halogen (7300) or pre-aligned xenon (7305) lamp is focused
onto the grating, with 1200 lines per millimeter, which separates the light into discreet wavelengths.
The diffracted spectrum of light then passes through a further slit and lens arrangement before passing
through the sample in the sample chamber from left to right. The light which is not absorbed by the
sample is transmitted through a collecting lens and onto the signal detector. The photo-diode detector
used is mounted directly onto the detector PCB and is used to calculate the % transmittance. The result
is displayed either as % transmittance or absorbance on the instrument display.
3.3 GooD PRACtiCe GUiDeLineS
1. For optimum performance all spectrophotometers should be sited in a clean, dry, dust free atmosphere.
When in use ambient temperature and light levels should remain as constant as possible.
2. If required adherence to Standard Operating Procedures (SOP) and Good Laboratory Practice (GLP)
should be monitored with regular calibration checks and a suitable Quality Control (QC) programme.
3. The sample chamber lid must be fully closed during measurement and before any readings are
recorded or printed.
4. The correct selection of sample containers is imperative for accurate and reproducible results:
a) Check that the material of the sample container is compatible with the wavelengths to be used
for measurement. In general glass can only be used down to 360nm or 320nm depending on quality.
Standard plastic cuvettes can be used down to 320nm. Special UV versions can be used down to
260nm. Below this level quartz cuvettes must be used.
b) Plastic disposable cuvettes should only be used ONCE.
c) Glass cuvettes should be thoroughly cleaned after use. Discard when scratches become evident on
optical surfaces.
d) Care should be taken when selecting semi-micro or micro cuvettes. The cuvette window on the
Entrance slit
Grating
Collimator mirror
Exit Slit
Detector
Collecting Lens
Sample
Lamp
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