Unicam UV 1 uv-visible spectrophotometer v1.30 was used for
analysis. Fresh vegetable samples were obtained from Dorayi ward,
forming part of Kumbotso Local Government, Kano, Nigeria. All
reagents used were of analytical-reagent grade. The vegetable sample
was chopped and ground in a porcelain mortar till homogeneous slurry
was formed. 10g of the slurry was taken into a 250cm3
beaker by
washing with 70 cm3
distilled water and 2.5ml of 4% NaOH was
added. The content of the beaker was warmed at 800
C for 25min with
occasional shaking. The resulting solution was filtered through a fluted
filter paper into 100 cm3 volumetric flask and made up to the mark. An
aliquot of 4 cm3
was taken into a test tube cooled in ice. 1 cm3
of 5%
Ag2SO4 solution was added followed by subsequent addition of 7 cm3
of 98% H2SO4 and 0.1 cm3
of 5% phenol solution. The solution was
allowed to stand for 20min while shaking occasionally. The resulting
mixture was extracted in 50 cm3
separating funnel by adding toluene
and shaking for 5 to 10min. The lower aqueous layer was discarded.
The organic phase was washed twice with 10ml of distilled water by
shaking for 2min and each time discarding the aqueous phase. The
organic phase was extracted again by shaking for 1 min with 10 cm3
of
10% Na2CO3 solution and collected in a test tube. Absorbance was read
at 407nm. Since 4cm3
of the 100cm3
filtrate was used for analysis.The
amount of nitrate (µg/g) in the vegetable was calculated by the formul