Quality control methods for

Determination of the rate of recovery 
Prepare five individual samples using each of the following procedures: 
1. To prepare solution S
2
, first dissolve separately 0.040 g of each of the 
reference substances, desmetryn R, prometryn R and simazine R, in 
sufficient acetone R to produce 100.0 ml. Then place 5.0 ml of each 
solution into a 100-ml volumetric flask and dilute the mixture to volume 
with acetone R (S
2
). Place 10.0 g of powdered plant material into a 500-ml 
conical flask and add 1.0 ml of solution S
2
. Shake this mixture 

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Quality control methods for medicinal plant materials 
mechanically for 60 minutes; if necessary, repeat the operation manually 
and then proceed as described under "Preparation of the plant material 
extract". Use either the purified or especially purified extract for the 
determination by gas chromatography, as specified in the test procedure 
for the plant material concerned. 
2. Treat 10.0 g of powdered plant material as described under "Preparation 
of the plant material extract". Use either the purified extract or the 
especially purified extract for the determination by gas chromatography, 
as specified in the test procedure for each individual plant material. 
Calculate the rate of recovery (R) in % using the following formula: 
c
b
a
)
-
( 
2
where a = average quantity in mg/kg of the 5 residues obtained using procedure 1,
b = average quantity in mg/kg of the 5 residues obtained using procedure 2,
c = quantity of reference substances in mg contained in solution S
2
during
procedure 1. 
The rate should be within the range 70-120%. It is specific for each drug.