Jenway 6850 - 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
propor tional 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. The quantitation
mode may be used to construct such a curve against which sample results are
automatically measured.
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. In the spectrum measurement mode a baseline scan must be performed before
performing a sample scan.