ASTM D3703 Test Method for Peroxide Number of Aviation Turbine Fuels
5. Apparatus
5.1 Iodine Number Flask, 250 mL, glass-stoppered.
6. Reagents
6.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
6.2 Purity of Water - Unless otherwise indicated, references to water shall be understood to mean reagent water conforming to Specification D1193, Type II.
6.3 Acetic Acid Solution - Mix 4 mL of concentrated hydrochloric acid (HCl, sp gr 1.19) with 996 mL of glacial acetic acid (CH3COOH (Warning - Poison Corrosive. Combustible can be fatal if swallowed. Causes severe burns. Harmful if inhaled. See A1.2)).
6.4 1,1,2-Trichloro-1,2,2 Trifluoroethane (Warning - See A1.1)
6.5 Potassium Dichromate Solution, Standard (0.1 N) - ACS reagent grade. Dissolve 2.452 g of the dried potassium dichromate (K2Cr2O7) in water and dilute to 500 mL in a volumetric flask. This solution is 0.1 N. As an alterative, the lab may use commercially prepared solution.
6.6 Potassium Dichromate Solution, Standard (0.01 N) (Warning - Avoid contact with eyes and skin and avoid breathing of dust) - Dilute 100 mL of 0.1 N K2Cr2O7 solution with water to 1000 mL in a volumetric flask.
6.7 Potassium Iodide Solution - Dissolve 120 g of potassium iodide (KI) in 100 mL of water. Larger quantities of solution may be prepared, provided the concentration of KI in water is equivalent. Discharge any color from this solution by placing 1 mL of KI solution, 50 mL of water, and 5 mL of starch solution in a 300-mL flask and blanketing with nitrogen or carbon dioxide. If a blue color develops, add 0.005 N Na2S2O3 solution from a microburet until color just disappears. Add a sufficient quantity of Na2S2O3 solution, thus determined, to the main KI solution to convert all free iodine to iodide. When properly prepared, 1 mL of KI solution should not turn blue when starch solution is added, but with starch plus one drop of 0.01 N K2Cr2O7 solution plus two drops of HCl, the blue color should develop. Store this solution under chloroform.
6.8 Sodium Thiosulfate Solution, Standard (0.1 N) - Dissolve 12.5 g of sodium thiosulfate (Na2S2O3•5H2O) plus 0.1 g of sodium carbonate (Na2CO3) in 500 mL of water (the Na2CO3 is added to stabilize the Na2S2O3 solution). Let this solution stand a week or more before using. As an alternative, the lab may use a commercially prepared solution. Standardize against 0.1 N K2Cr2O7 solution, using any appropriate technique, such as the one indicated in 4500-C1 B. Standardize at intervals frequent enough to detect changes of 0.0005 in normality.
6.9 Sodium Thiosulfate Solution, Standard (0.005 N) - Prepare a twenty-fold dilution of the 0.1 N Na2S2O3 solution prepared in 6.8, using a volumetric flask. One way to accomplish this is to dilute 100 mL of 0.1 N Na2S2O3 solution with water to 2000 mL in a volumetric flask. Prepare this solution fresh with restandardized 0.1 N Na2S2O3 solution when any change of 0.0005 or over in normality is detected.
6.10 Starch Solution - Make a paste of 6 g of arrowroot starch or soluble iodometric starch with cold water. Pour the paste into 1 L of boiling water. Add 20 g of potassium hydroxide (KOH), mix thoroughly, and allow to stand for approximately 2 h. Add 6 mL of glacial acetic acid. Mix thoroughly and then add sufficient HCl (sp gr 1.19) to adjust the pH value of the solution to 4.0. Store in a glass-stoppered bottle. Starch solution prepared in this manner can remain chemically stable for up to one year. As an alternative, the lab may use a commercially prepared solution (some are preserved with salicylic acid).
7. Sampling
7.1 Samples shall be taken in accordance with the procedures described in Practice D4057.
