Jenway 6305 - Manual (Page 17)

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h) Flow-through cuvettes must be selected with care and consideration for the
sample type, sample volume, pumping system, rinse, sample and waste handling
to be used.
5. Samples and standards should not be stored in open cuvettes or sample containers
as evaporation will change the value and lead to staining of the walls which may be
irreversible. If stored in stoppered and sealed cuvettes, they should be filled with little
or no air space and the values regularly checked against a reference standard or
quality control material.
6. Samples should be allowed to equilibrate to ambient temperature before
measurement (unless a suitable temperature controlled sample holder is in use).
Temperature change during measurement may cause air bubbles to form on the
walls of the sample holder. This is a common cause of drift during measurement.
7. In the preparation of samples and standards high grade borosilicate glass and AR
grade chemicals and reagents must be used. Good quality deionised water or other
suitable solvents must be used for dissolving or diluting samples, chemicals and
reagents.
8. All measurements require calibration to a blank, for maximum accuracy this should be
prepared with care using the same deionised water or solvent used for dissolving or
diluting the sample. Where reagents are added to the sample to produce a colour
proportional to its concentration a ‘sample based’ blank should be used. In this case
the blank should consist of all reagents or chemicals to be used, except the sample
which will produce the colour to be measured.
9. Deviations from the Beer-Lambert Law may occur at high and low concentrations
giving non-linear response during sample concentration measurements. For all new
methods a linear range should be defined by the preparation of a calibration curve.
10. Cuvettes and sample holders must be filled to a minimum level which covers the light
path. All Jenway spectrophotometers have a beam height of 15mm.
11. The instrument must be calibrated to zero absorbance/100% transmittance prior to
taking readings.