Determination of paraquat and diquat by Surface Enhanced Raman
Scattering (SERS)


Yvonne Carella, Christine M. Davidson & W. Ewen Smith

Department of Pure and Applied Chemistry, University of Strathclyde, 295
Cathedral Street, GLASGOW G1 1XL, UK

                   
Pollution from pesticides is of increasing concern.  It is therefore
necessary to develop sensitive, molecularly-specific methods for the
detection of these compounds in the environment.  Raman spectroscopy is
potentially useful in this context as it provides a vibrational spectrum for
a given analyte, and has the potential to be used in situ.  The limited
sensitivity of conventional Raman scattering can be improved by use of
surface-enhanced Raman scattering (SERS).

Paraquat and diquat were analysed in colloidal suspension with an
aggregating agent using a 514.5 nm laser.  The conditions were optimized for
the technique and the lowest concentrations monitored were at pg/L levels.
It is commonly known that paraquat and diquat produce coloured free radical
species when reduced using sodium dithionite.  Paraquat gives a blue
coloured free radical and diquat produces a green species.  It was thought
that the reduction of these pesticides could increase the sensitivity of the
technique.  The free radicals were analysed in colloidal suspension and also
gave good results at the pg/L.