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An
Ultra Violet spectrophotometer works by passing ultra violet
“light” through the sample and measuring the
amount of light transmitted at a number of different wavelengths.
In the Authenticator some 256 wavelengths between 180 nm
(deep UV) and 450nm (visible blue) are measured. This information
is stored in the Authenticator, but can also be downloaded
and displayed on a PC.
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A
Typical Ultra Violet Spectrum of Whisky
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Spectrophotometers
are comparison instruments, so each set of measurements
whether of genuine products or unknown samples must be compared
to the measurement of a fixed standard. This can be air
(i.e. nothing in the cell), distilled water, or normally
in spirit authentication, a mixture of 40% ethanol in water.
This measurement of the fixed standard is given a value
of 100% transmission at all wavelengths, and subsequent
sample measurements are compared to this.
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first step it is necessary to establish the spectrum of the
genuine products. As different production batches may vary
slightly, we recommend measuring some 8 – 10 samples
and taking an average. It is then necessary to set a tolerance
around this to allow for this variation in samples tested
in the field. |
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Genuine
product plus tolerances
In operation the user scrolls down a list of brands
stored in the Authenticator to find the supposed product.
A sample of the suspect product is then measured and
the curve compared to the stored curve and tolerance
limits.
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If
the measurement falls within the tolerance, a green light
is illuminated and PASS appears on the display. If just
outside the tolerance, an amber light is illuminated and
FAIL appears on the display. If significantly different
from the genuine curve, a red light is illuminated, and
FAIL appears on the display.
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Information
on all samples is stored in the memory of the Authenticator,
together with date and time information, for subsequent
downloading and analysis.
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