Iron occurs in the minerala as hematite, taconite and pyrite. It is widely used in steel and other alloys Elevated iron levels in water can cause stains in plumbing, laundry and cooking utensils and can impart objectionable taste and colour to foods.
Phenanthroline method:
Principle:
Iron is brought into solution, reduced to the ferrous stste by boiling with acid and hydroxylamine, and treated with 1, 10-phenanthroline at pH 3.2 to 3.3. Three molecules of phenanthroline chelate each atom of rerrous ironto form an orange-red complex. The coloured solution obeys Beers's law, it's intensity is independent of pH from 3 to 9. The presence of an exess of phenanthroline insures rapid colour development in the pH range between 2.9 to 3.5. Colour standars are stable for at least 6 months.
Instrument and Equipment:
• Spectrophotometer
PURPOSE:
To describe the Laboratory standard operating procedure for measurement of Iron by Colorimetric method in Water and Waste Water samples.
SCOPE:
Applicable to the Laboratory for analysis of Water and Waste Water samples, where measurement of Iron by colorimetric method is required.
RESPONSIBILITY:
Lab chemist
:
Analysis of sample for measurement of Iron by colorimetric method.
Technical Manager
:
Review of activity
Quality Manager
:
Implementation and compliance of SOP.
PROCEDURE:
Principle:
Iron is brought into solution ,reduced to the ferrous state by boiling with acid and hydroxylamine, and treated with 1,10-phenanthrolin at pH 3.2 to 3.3. Three molecules of phenanthroline chelate each atom of ferrous iron to form an orange res complex. The colored solution obeys Beer’s law ; its intensity is independent of pH from 3 to9. A pH between 2.9 and 3.5 insures rapid color development in the presence of an excess of phenanthroline.
Instrument and Equipment:
Spectrophotometer
Reagents:
Hydroxylamine solution: Dissolve 10.0gm of Hydroxylamine in 100mL of water
Ammonium Acetate buffer Solution: Dissolve 250 gm of Ammonium Acetate in 150 ml water. Add 700 mL conc. Glacial acetic acid.
Sodium acetate solution: Dissolve 200 gm Sodium acetate in 800 mL water.
Phenanthroline Solution: Dissolve 100 mg 1,10-phenanthrolin monohydrate in 100ml water by stirring and heating to 80°C. Do not boil.
Potassium permanganate 0.1M: Dissolve 0.316 KMnO4 in distilled water and make up to 100mL.
Stock Iron Solution: dissolve 1.404 gm of Ferrous Ammonium Sulphate in 50mL water , add 20mL conc. H2SO4..Dilute to 1000mL with water and mix. 1.00mL=200µg Fe.
Standard Iron solution:Pipet 50.0mL stock solution into a 1000mL volumetric flask and dilute to mark (1.0mL= 10.0µg Fe)
Pipet 5.00mL stock solution into a 1000mL volumetric flask and dilute to mark (1.0mL= 1.0µg Fe)
Test Method:
Filtered the sample through filter paper in to a cleaned conical flask, if necessary
Prepare the Iron standards in the range of 1 to 5 mg/l Fe.
Set the photometer to zero absorbance with blank solution and obtain absorbance reading of standards.
Plot a graph against absorbance and concentration
Pipette 50ml of the sample in to 100ml volumetric flask.
Add 2 ml of Hcl and 1ml of hydroxylamine hydrochloride ,add few glass beads and heat to boiling.
To insure dissolution of iron, continue boiling until volume is reduced to 15 to 20 ml.
Cool to room temperature and transfer to 100 ml , add 10 ml of Ammonium acetate
buffer and 4 ml of 1,10 phenanthroline and dilute to mark with water, Mix thoroughly
and allow for 10 min and see absorbance at 510 nm using spectrophotometer.
If the absorbance beyond the range of the standard curve, repeat using a diluted sample.
Prepare a blank in which 50ml of distilled water is substituted for the sample.
Calculation:
Fe mg/L = µg Fe (in 100ml final volume)
mL of sample
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