A New Colorimetric Method for the Microdetermination of Pyrethrins

A new colorimetric method for the microdetermination of pyrethrins
in the presence of pyrogallic acid, an antioxidant and other adjuvants,
is described. pyrethrins react with sulphuric acid to yield a colour
complex, which has medium absorbance at 263 mu. Complete
colour reaction requires heating for 10 min at 100°C. The colour
cOmplex is stable for a long period and Beer's law is obeyed in the
range 1-120 ug pyrethrins. Sufficient absorbance is obtained when
Sulphuric acid of 80-98% strength is used. Of the several solvents tested
for their effect on the colour reaction, ethyl alcohol, ethyl acetate and
trichloroethylene did not interfere. Hexachlorocyclohexane, lindane
and aldrin when incorporated with pyrethrins did not affect the colour
Complex. The method developed is specific and rapid. It is highly
sensitive, enabling the estimation of pyrethrins at as low as 1 ug level.