Girijavallabhan, C P; Nampoori, V P N; Radhakrishnan, P; Sheeba, M; Rajesh, M(Measurement Science and Technology, Institute of Physics Publishing, October 4, 2005)
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Abstract:
The design and development of a fibre optic evanescent wave refractometer
for the detection of trace amounts of paraffin oil and palm oil in coconut oil
is presented. This sensor is based on a side-polished plastic optical fibre. At
the sensing region, the cladding and a small portion of the core are removed
and the fibre nicely polished. The sensing region is fabricated in such a
manner that it sits perfectly within a bent mould. This bending of the
sensing region enhances its sensitivity. The oil mixture of different mix
ratios is introduced into the sensing region and we observed a sharp decrease
in the output intensity. The observed variation in the intensity is found to be
linear and the detection limit is 2% (by volume) paraffin oil/palm oil in
coconut oil. The resolution of this refractometric sensor is of the order of
10−3. Since coconut oil is consumed in large volumes as edible oil in south
India, this fibre optic sensor finds great relevance for the detection of
adulterants such as paraffin oil or palm oil which are readily miscible in
coconut oil. The advantage of this type of sensor is that it is inexpensive and
easy to set up. Another attraction of the side-polished fibre is that only a
very small amount of analyte is needed and its response time is only 7 s.