【Weekly Topic】(41) September 2, 2015: What are the two methods for determining the total iron content in water? What is used as the color-developing agent for each?

Just precipitate the ferrous and ferric ions – it’s using caustic soda solution, I guess

O-phenanthroline colorimetry, using o-phenanthroline as a colorimetric reagent

Colorimetry, spectrophotometry; potassium thiocyanate, diazophenyl

What are the two methods for determining the total iron content in water? What is used as the color-developing agent for each? Answer: There are generally two methods for determining the total iron content in water: the sulfosalicylic acid spectrophotometry method and the o-phenanthroline spectrophotometry method. In the sulfosalicylic acid method, ferrous ions are oxidized to ferric ions before measurement, with sulfosalicylic acid being used as the color-developing agent; the applicable range for this method is total iron contents greater than 0.4 mg/L. In the o-phenanthroline method, ferric ions are reduced to ferrous ions before measurement, using o-phenanthroline as the color-developing agent; the applicable range for this method is 0.02–20 mg/L

Reagents and solutions: Salt; Acid: 6 mol/L or 3 mol/L solution; Ammonia water: 10% or 2.5% solution; Sulfuric acid, glacial acetic acid, sodium acetate, acetic acid-sodium acetate buffer solution (pH = 4.5); Salicylhydrazine acid: 2% solution; Ophenanthroline: 0.2% solution; Ammonium ferric sulfate, iron standard solution. Preparation of the iron standard solution: Weigh 0.863 g of ammonium ferric sulfate, to an accuracy of 0.001 g, and place it in a 200 ml beaker. Add 100 ml of water and 10 ml of sulfuric acid; after dissolution, transfer the entire mixture to a 1000 ml volumetric flask and dilute with water to the mark, then mix well. Transfer 50.0 ml of this iron standard solution to a 500 ml volumetric flask, dilute to the mark, and mix well. Analysis steps: 1. Take 6 volumetric flasks and add 0, 1.00, 2.00, 4.00, 6.00, 8.00, and 10.00 ml of the iron standard solution to each respectively. Perform the following operations for all of them as well: add about 60 ml of water, adjust the pH to around 2 using salt acid, check the pH value with a precise pH paper, add 2.5 ml of salicylhydrazine acid, 10 ml of acetic acid-sodium acetate buffer solution, and 5 ml of ophenanthroline, then dilute with water to the mark and mix well. 2. Use a cuvette of appropriate thickness; at the maximum absorption wavelength (around 510 nm), use water as the reference and adjust the absorbance of the spectrophotometer to zero before measuring the absorbance. 3. Subtract the absorbance of the reagent blank test from the absorbance of each standard solution. Plot a standard curve with the iron content on the horizontal axis and the corresponding absorbance on the vertical axis. Store properly

Method for determining ferrous iron by reducing trivalent iron with ascorbic acid, followed by color development with o-phenanthroline and measurement of absorbance at 510 nm

1. Ophenanthroline spectrophotometry: Reagent – ophenanthroline. 2. Diazophenanthroline spectrophotometry: Reagent – 1,10-diazophenanthroline

There are generally two methods for determining the total iron content in water: the sulfosalicylic acid spectrophotometry method and the o-phenanthroline spectrophotometry method. The sulfonate method involves oxidizing divalent iron to trivalent iron for simultaneous determination; sulfosalicylic acid is used as the color-developing agent, with a detection range for total iron content of greater than 0.4 mg/L ； The adjacent method involves reducing trivalent iron ions to divalent iron ions and then measuring them together; using o-phenanthroline as a color-developing agent, the measurement range is 0.02–20 mg/L

Sulfosalicylic acid method, Sulfosalicylic acid; O-phenanthroline method, O-phenanthroline

There are generally two methods for determining the total iron content in water: the sulfosalicylic acid spectrophotometry method and the o-phenanthroline spectrophotometry method. In the sulfate method, ferrous ions are oxidized to ferric ions before measurement, with sulfosalicylic acid being used as the color-developing agent; this method is suitable for total iron concentrations above 0.4 mg/L. In the o-phenanthroline method, ferric ions are reduced to ferrous ions before measurement, using o-phenanthroline as the color-developing agent; its applicable range is from 0.02 to 20 mg/L