imidacloprid solution was transferred to each conical flask
for 0.02 and 0.20 ppm fortification levels. In case of water,
samples at pH 4, 7 and 9 (25 mL) were transferred into
volumetric flask 50 mL capacity and fortified with imidacloprid
at LOQ and 10 9 LOQ levels separately. A Volume
of 0.25 and 2.5 mL imidacloprid was transferred to
each volumetric flask for 0.02 and 0.20 ppm fortification
levels. The control samples were processed similarly where
in 0.25 and 2.5 mL acetonitrile was added.
A volume of 100 mL methanol was transferred into the
Erlenmeyer flask containing (50 g) fortified soil sample
and allowed to stand for 2 h. The Erlenmeyer flask was
placed onto orbital shaker for 30 min. After shaking, the
solutions were filtered into the round bottom flask of
500 mL capacity through Whatman filter paper No.1
bearing a bed of anhydrous sodium sulphate. Solvent was
removed using vacuum evaporator. The residual cake was
re-extracted twice with additional volume of 50 mL
methanol. The methanol extracts were collected, pooled
and concentrated to smaller volume (5–10 mL) using
vacuum evaporator at B40C. The concentrated extract
was subjected to further clean up by column chromatography.
A glass column packed with florisil as adsorbent
placed in between two layer of anhydrous sodium sulphate
was employed. The column was pre-conditioned with
methanol and concentrated extracts were loaded onto top of
the column and eluted with 100 mL acetonitrile @ 2 mL/
min. Eluate was concentrated to dryness using rotary
vacuum evaporator at B40C and residue re-dissolved in
5 mL acetonitrile. The samples were transferred into volumetric
flask 10 mL capacity using Whatman No. 1 filter
paper and final volume was made up to the mark with
acetonitrile.
The fortified water samples (25 mL) at different pH viz.
4, 7 and 9 were transferred separately into a separating
funnel of 250 mL capacity and a volume of 50 mL ethyl
acetate was added into it. The separating funnel was shaken
manually for 5 min with frequent vent. The contents of the
separating funnel were allowed to stand for 10 min for
layer separation. The ethyl acetate organic layer was collected
into a round bottom flask of 500 mL capacity. The
aqueous layer was re-extracted twice with additional volume
of 50 mL ethyl acetate and collected in the same
round bottom flask. The combined extract was concentrated
to dryness using rotary vacuum evaporator at B40C
temperature. The residue was re-dissolved in 5 mL acetonitrile.
The samples were transferred into volumetric flask
of 10 mL capacity through Whatman No. 1 filter paper and
final volume was made up to the mark with acetonitrile.