 Commonwealth of Australia 2002

Appendix 5

DRAFT UNPUBLISHED ANALYTICAL PROCEDURE FOR PEROXIDE VALUE
FRAGRANCE MATERIALS ASSOCIATION (FMA)

FMA Instrumental Analysis and Specifications Committee

PEROXIDE VALUE

Definition

“Peroxide value = millimoles peroxide/liter”

A. Reagents:

1. 
   Potassium Iodide, saturated aqueous solution, (freshly prepared).
   
2. 
   Solvent Mixture 1: Glacial Acetic Acid: Chloroform (3:2).
   
3. 
   Solvent Mixture 2: Glacial Acetic Acid: Cyclohexane (3:2).
   
4. 
   Indicator: (Starch Solution or Thyodene)
   
5. 
   0.1N Sodium Thiosulfate, volumetric solution (v.s) (0.1N Na₂S₂O₃).
   
6. 
   0.01N Sodium Thiosulfate, volumetric solution (v.s.) (0.01N Na₂S₂O₃). (Prepare Fresh Monthly)
   a. Prepare by pipetting 10.0 ml. of 0.1N Na₂S₂O₃ into a 100 ml. volumetric flask and diluting to volume with distilled
   water.
   
7. 
   Benzoyl Peroxide: 97% minimum (Aldrich Chemical). If 97% Benzoyl Peroxide is not available, any suitable peroxide may be used as a substitute so long as the concentration is taken into consideration in the calculations.
   
8. 
   Methanol (Methyl Alcohol), Reagent grade
   

PROCEDURAL NOTE 1: There are laboratories which do not permit the use of chlorinated solvents. Two solvent systems (Reagents 2 and 3) are provided to address this concern.
PROCEDURAL NOTE 2: Use 0.1N Na₂S₂O₃ when expected peroxide values are over 20 mmol/L.

Use 0.01N Na₂S₂O₃ when expected peroxide values are less than 20 mmol/L.

PROCEDURAL NOTE 3 : This procedure may be performed using mechanical or manual mixing. When using mechanical mixing, a 250 ml. Erlenmeyer flask can be used. When manual mixing and shaking is performed, a 250 ml. Iodine flask is used.
PROCEDURAL NOTE 4: To assure the accuracy of the data, the appropriate standards (as prepared in section D) should be analyzed concurrently with the samples being tested.
B. Procedure:

1. 
   Transfer 10.0 ml. of sample and 50 ml. of the appropriate solvent mixture into the flask and stir at a slow speed or gently shake.
   
2. 
   Add 1.0 ml. of saturated potassium iodide solution and stir at a slow speed or gently shake for 1 minute.
   
3. 
   Add 100 ml. of distilled water and 1 ml. starch solution or 0.1 g of Thyodene indicator.
   
4. 
   Mix aggressively (high speed stirring) or shake well and immediately titrate with 0.1N or 0.01N Na₂S₂O₃ from a purple to a
   slightly yellow or colorless endpoint. (Note: these colors may be affected by the initial color of the test material).
   

C. Calculation

Peroxide Value (Millimoles Peroxide/Liter) = ml. _(titrant)  N _(titrant) 50

Note: Peroxide values may also be calculated as milliequivalents of peroxide. For example, the AOCS method used for fatty oils calls for a weighed sample and calculation as milliequivalents of peroxide per 1,000 grams of sample. Values calculated thus will be approximately twice those calculated by the FMA method.
D. Preparation of Benzoyl Peroxide Standards:

1. 
   Standard 1: (approx 2.0 mmol/L)
   
   1. 
      Accurately weigh approximately 0.005g. of Benzoyl Peroxide into a 10 ml. volumetric flask and add approximately 9 ml. of methanol. Mix until dissolution is complete (Gently warm if necessary). If the solution is warmed, cool to room temperature and dilute to volume with Methanol. Mix well. Calculate concentration as per step 4.
      
2. 
   Standard 2.: (approx. 6.0 mmol/L)
   
   1. 
      Accurately weigh approximately 0.015 g. of Benzoyl Peroxide into a 10 ml. volumetric flask and add aprroximately 9 ml. of methanol. Mix until dissolution is complete (Gently warm if necessary). If the solution is warmed, cool to room temperature and dilute to volume with Methanol. Mix well. Calculate concentration as per step 4.
      
3. 
   Standard 3.: (approx. 18.0 mmol/L)
   
   1. 
      Accurately weigh approximately 0.045g of Benzoyl Peroxide into a 10 ml. volumetric flask and add approximately 9 ml of methanol. Mix until dissolution is complete (Gently warm if necessary). If the solution is warmed, cool to room termperature and dilute to volume with Methanol. Mix well. Calculate concentration as per step 4.
      
4. 
   Calculation of standard concentration:
   
   1. 
      Wt.std. (g.) _(Adjusted) × 100  0.2423 = mmol/L
      
      1. 
         wt.std (g.) (Adjusted) = (wt of standard × percent of standard) / 100
         
5. 
   Calculation of mmol/L peroxide in standard
   
   1. 
      Millimoles Peroxide / Liter = ml. _(titrant)× N _(titrant)× 50
      

NOTE 1: No more than 5% error should be found between the calculated and titrated values. Methanol can be run as a blank.

NOTE 2: The committee recommends that the peroxide analyses should be validated by running the appropriate standards concurrently with the sanples.

DISCLAIMER FOR METHOD FOR DETERMINATION OF PEROXIDES:

This method is comparable to other methods used in the scientific community employing similar chemistry. However, after collaborative testing and comparisons of data, the FMA Instrumental Analysis and Specifications Committee has concluded that there may be competing reactions inherent in certain materials which may complicate the endpoint and thus can affect the accuracy of the method. (Note: This phenomena has also been observed using comparable procedures). It is recommeded that replicate analyses be performed.

References

ABS (Australian Bureau of Statistics) (2000) 1996 Census of Population and Housing – Basic Community Profile. Canberra, Commonwealth of Australia. Available from the following URL:

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