2.3.2.1. Method 7196A (colorimetric method for hexavalent chromium)
This is an accepted method for the estimation of dissolved hexavalent chromium in ground water. It is mainly used for certain domestic and industrial waste for the quantification of Cr (VI). For the quantification of Cr (VI) between a ranges from 0.5 to 50 ppm, this is the widely accepted method.
Briefly, 95 ml of ground water sample was taken in a beaker/flask. To it, 2.0 ml of colouring reagent diphenylcarbazide solution was added. It was then acidified to pH 2.0 ± 0.5 using 0.1 M H2SO4. Next, it was incubated for an about 7 to 10 minutes for the colour development. After the incubation period, the colour intensity was read at 540 nm against Cr (VI) standard series.
2.3.2.2. Method…show more content… To this, 2 drops of Bromophenol blue indicator was added. Next, 1 M sodium hydroxide solution was added until blue colour remains in the solution. Afterwards, pH was adjusted using 0.12 M sulphuric acid till blue colour disappears in the solution and again 1 ml of 0.12 M sulphuric acid was added in excess to make the pH 2.4. In the next step, 5.0 ml of APDC was added and mixed properly and at this point pH was 2.8. Following this, 10.0 ml of MIBK was added and shook vigorously for 3 to 5 minutes. Ketone layers were allowed to get separated from water and then Milli Q water was added until the ketone layer reached to the neck of volumetric flask. With the help of Flame Atomic Absorption Spectrophotometer, ketone layer was aspirated and estimated the concentration of Cr (VI) with standard series and against…show more content… Extraction of estimation of total chromium from soil samples
For this, 2.5 g of soil was taken in a conical flask. To this, 1.0 ml of 2.0 N H2SO4 with 20.0 ml HNO3 and 3.0 ml H2O2 was added. The sample was then heated upto dryness. After that, 3.0 ml of concentrated nitric acid and 1.0 ml H2O2 was added to remove organic constituents from soil. The residue was dissolved with 1.0 ml of 2.0 N H2SO4 and 10.0 ml of Milli Q water followed by filtration with 0.45 μM whatman 540 filter paper. Finally, it was diluted upto 100 ml in volumetric flask for the determination of total chromium using flame atomic absorption spectrophotometer.
2.3.2.5. Extraction of estimation of trivalent chromium from soil samples
Here, 1.0 ml of 2.0 N H2SO4 was added in the soil residues obtained by alkaline digestion method described above. Next, 20.0 ml concentrated nitric acid with 3.0 ml hydrogen peroxide was added to the residues and was heated to almost dryness. Later, 3.0 ml concentrated nitric acid and 1.0 ml H2O2 was added to remove organic constituents from soil. The residue was dissolved with 1.0 ml of 2.0 N H2SO4 and 10.0 ml of Milli Q water followed by filtration with 0.45 μM whatman 540 filter paper. Finally it was diluted upto 100 ml in volumetric flask for the determination of trivalent chromium using flame atomic absorption