Page 110 - The Veterinary Laboratory and Field Manual 3rd Edition

The selection, use, maintenance and quality control of laboratory equipment and supplies 79

specimen is polychromatic light but within a
narrow range (for example, an Ilford blue filter
has wavelength range of 450–480 nm). Most
regional laboratories will have a simple spectro-
photometer, which can operate at wavelengths
in the visible spectrum between, for example,
345 and 750 nm (see Chapter 7 and Figure 2.44).
The majority of quantitative methods used in
clinical chemistry result in a coloured product,
which can be measured. In most cases the inten-
sity of colour is directly related to the amount
of substance in a solution, that is, the more
intense the colour the higher the concentration
of the substance in the sample. Measurements
are made on either (1) the amount of light
absorbed by the sample (absorbance) or (2)
the amount of light passing through the sample
(transmittance). The sample (coloured solu-
tion) is usually held in a cuvette. Cuvettes are
small volume receptacles made of special glass
or re-useable or disposable plastic. Most manu-
Figure 2.43 Dispenser. Photo: Willy Schauwers, facturers guarantee that each batch is matched
Provincial Institute for Hygiene, Antwerp.
for consistency and precision. The manufacturer
will provide details on how to use the spectro-
ranges and are supplied with a range of adap- photometer/colorimeter and the methodologies
tors to fit commonly used reagent bottles. The
dispensers must be used in such a way that
no air-bubbles are dispensed while adding the
reagent.
Follow the same quality assurance as for
mechanical automatic pipettes.

colorimetry equipment and
spectrophotometer

Colorimeter and spectrophotometer are names
given to instruments that produce and then mea-
sure light which passes through or is absorbed
by a coloured solution representing the sample. Figure 2.44 Semi-automatic photometer, Rayto
Spectrophotometers use a diffraction grating RT-9200 (wavelengths in the visible spectrum between
prism to produce monochromatic light to pass 330–800 nm, five standard filters, three optional filters,
through the sample whereas colorimeters use flow cell. Photo: Tom Gernaey, Tactilab RDC, Brussels,
filters and the light that passes through the Belgium.

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