Methods for Product Assay Methods for Residual Peroxide Determination Additional Information

Titanium Oxalate (Spectrophotometric)

Principle

The sample is clarified by treatment with aluminum chloride and sodium hydroxide solution and the hydrogen peroxide reacted with potassium titanium oxalate in acid solution to form the yellow pertitanic acid complex. The colored complex is measured spectrophotometrically at 400 nm.

Scope of Application

This method is suitable for the determination of hydrogen peroxide in aqueous effluents and raw sewage in the range 0.1 - 50 µg/mL (or 0.1 - 50 mg/L) as H2O2.

Interferences

Formation of the peroxotitanium complex is specific to hydrogen peroxide. However, wastewaters possessing a strong yellow background color may affect accuracy. Normal background color can be reduced by filtering the sample, or compensated for by zeroing out a blank of unreacted sample. The method includes a flocculation pretreatment step to remove suspended matter – the AlCl3 - NaOH pretreatment step may be omitted when analyzing clear waters.

Safety Precautions

Potassium titanium oxalate is a toxic material and should be handled and disposed of in accordance with the MSDS. Neoprene gloves and monogoggles are recommended.

Concentrated sulfuric acid and sodium hydroxide are corrosive, hazardous materials and should be handled and disposed of in accordance with the MSDS. Neoprene gloves and monogoggles are recommended, as is working under a vacuum hood.

Sample bottles containing H2O2 should not be stoppered, but rather vented or covered loosely with aluminum foil or paraffin film.

Reagents

All reagents should be of analytical reagent grade unless otherwise stated

1. Potassium permanganate solution (0.1N)
2. Aluminum chloride solution (484 g/L)
   Dissolve 121 g of aluminum chloride hexahydrate in 150 mL of demineralized water. Dilute to 250 mL with demineralized water in a measuring cylinder and mix well.
3. Potassium titanium oxalate solution (50 g/L)
   Dissolve 25 g of potassium titanium oxalate, in 400 mL of demineralized water, warming if necessary. Cool and dilute to 500 mL with demineralized water in a measuring cylinder and mix well.
   Warning: Potassium titanium oxalate is toxic and solutions must be handled using a safety pipette or burette.
4. Sodium hydroxide solution (240 g/L)
   Dissolve 60 g of sodium hydroxide in 150 mL of demineralized water, dilute to 250 mL with demineralized water in a measuring cylinder and mix well.
5. Sulfuric acid solution (1+9)
   Slowly add 50 mL of sulfuric acid, d 1.84, with continuous stirring to 450 mL of demineralized water in a 1 liter beaker. Cool.
   Note: Safety goggles must be worn when handling concentrated sulfuric acid.
6. Sulfuric acid solution (1 + 17)
   Slowly add 20 mL of sulfuric acid, d 1.84, with continuous stirring to 340 mL of demineralized water in a 1 liter beaker. Cool.
7. Standard hydrogen peroxide solution (stock) 1 mL = 1000 μg
   Add 7.50 mL of hydrogen peroxide solution (275 g/Kg) to a 2 liter volumetric flask, dilute to volume with demineralized water and mix well.
   This solution must be standardized as described below on the day of use.
   Using measuring cylinders, add 10 mL sulfuric acid solution (1 + 9) and 50 mL of demineralized water to a 250 mL conical beaker. Add potassium permanganate solution (0.1N) dropwise to the appearance of a faint permanent pink color.
   Pipette 50.0 mL of hydrogen peroxide solution (stock) into the flask and titrate with potassium permanganate solution (0.1N) to the reappearance of the same permanent pink color. Let the titration obtained be T mL.
   Then the concentration of the hydrogen peroxide solution (stock) = ((T x N x 17 x 1000 x 1000 x 1000) / (1000 x 50 x 1000)) μg/mL = T x N x 340 μg/mL
   Where N is the normality of the potassium permanganate solution.
   Let this concentration be G μg/mL.
8. Standard hydrogen peroxide solution (working) 1 mL = 100 μg
   Pipette 25.0 mL of hydrogen peroxide solution (stock) into a 250 mL volumetric flask. Dilute to volume with demineralized water and mix well.
   Then the concentration of the hydrogen peroxide solution (working) = G/10 μg/mL
   This solution must be freshly prepared on the day of use.

Apparatus

Spectrophotometer capable of measuring absorption at a wavelength of 400 nm and fitted with 10 mm and 40 mm pathlength glass cells.

Procedure

Preparation of Calibration Graph

From a burette add the volumes of hydrogen peroxide solution (working) shown in the table below into a series of 25 mL volumetric flasks.

Volume of Standard Hydrogen Peroxide solution (working) (ml)	0.0	1.0	2.0	3.0	4.0	5.0	6.0
Mass of Hydrogen Peroxide taken (ug)	0.0	1.0 x (G/10)	2.0 x (G/10)	3.0 x (G/10)	4.0 x (G/10)	5.0 x (G/10)	6.0 x (G/10)

Using a safety pipette add 2.5 mL of sulfuric acid solution (1 + 17) and dilute each solution to about 20 mL by adding suitable volumes of demineralized water. Mix well and using a safety pipette add 2.0 mL of potassium titanium oxalate solution (50 g/L). Dilute each solution to volume with demineralized water and mix well.

Measurement of Standard Solutions

Set the spectrophotometer to measure absorption at a wavelength of 400 run and select a pair of 10 mm pathlength glass cells.

Adjust the instrument for zero absorption against demineralized water in one of the cells. Using the other cell measure in turn the absorption of each of the standard solutions.

Subtract the absorption of the standard solution containing no added hydrogen peroxide from that of the remaining standard solutions.

Plot the optical densities against the corresponding hydrogen peroxide content of the standard solutions.

Draw in the line of best fit through the series of points and the origin to obtain the required calibration graph.

Repeat the measurements using 40 mm glass cells for the solutions containing up to 5.0 mL of standard hydrogen peroxide (working) solution.

Preparation and Analysis of Sample Solutions

Fill a 500 mL glass bottle with the sample, if possible directly from the source of supply, by means of a rubber tube passing to the bottom of the bottle. Allow the sample to flush out the bottle for two minutes then withdraw the tube and stopper the bottle.

Pipette into the bottle 1.0 mL of aluminum chloride solution (484 g/L) and 1.0 mL of sodium hydroxide solution (240 g/L) with the pipette tips beneath the surface of the liquid. Allow any surplus sample to overflow from the bottle. Replace the stopper and mix the contents by inverting the bottle several times. Allow the precipitate to settle.

Pipette 20.0 mL of the supernatant liquor from the clarified sample into a clean 25 mL volumetric flask.

Prepare a reagent blank solution by pipetting 20.0 mL of demineralized water into a clean 25 mL volumetric flask.

Treat the sample and blank solutions exactly as described under Preparation of Calibration Graph from "using a safety pipette add 2.5 mL of sulfuric acid solution (1 +17) ..."

Prepare a sample blank solution by pipetting 20.0 mL of the supernatant liquor from the clarified sample into a 25 mL volumetric flask. Add 2.5 mL of sulfuric acid solution (1 + 17) and dilute to volume with demineralized water.

Measure the absorption of the sample solution, the sample blank solution and the reagent blank solution as described. Subtract the absorption of the sample blank solution and the absorption of the reagent blank solution from that of the test solution.

Relate the optical density so obtained to the calibration graph to obtain the weight of hydrogen peroxide. Let this weight be A µg as H2O2.

Calculation

Hydrogen peroxide content (as H₂O₂) = (A/20) mg/L

Sourcing for Titanium Reagent

Titanium potassium oxalate

Alfa Aesar: (978) 521-6401 http://www.alfa.com/
City Chemical: (800) 248-2436 http://www.citychemical.com/
MP Biomedicals: (800) 854-0530 http://www.mpbio.com/
Pfaltz & Bauer: (203) 574-0075 http://www.pfaltzandbauer.com/

References
Solvay Chemicals, Inc.