ASTM D6447 Standard Test Method for Hydroperoxide Number of Aviation Turbine Fuels by Voltammetric Analysis
8. Procedure
8.1 Electrode Cleaning Solution Preparation - Transfer equal amounts of the acetic acid solution and distilled water into a 5 mL glass vial. One way to do this is to use separate pipettes for each material that can deliver a 2 mL volume.
8.2 Blank Preparation (0 mmole) - Into a 5 mL glass vial, in succession, pipette 1 mL of KCl solution, 1 mL of acetic acid solution, and 0.2 mL of KI solution. Reversal of mixing order will result in high blank readings of the voltammetric analyzer calibration. Cap the vial and shake for 5 s using a vortex mixer (see 5.2).
8.3 Standard Preparation (1 mmole) - Into a 5 mL glass vial, in succession, pipette 1 mL of 0.002 N K2Cr2O7 solution, 1 mL of acetic solution, and 0.2 mL of KI solution. Cap the vial and shake for 5 s using a vortex mixer (see 5.2).
8.4 Calibration:
8.4.1 The voltammetric analyzer used in this test method gives linear results between 0.2 and 2 mmole. Below 0.1 mmole, the signal to noise ratio becomes large. Although the voltammetric analyzer is linear between 0.1 and 2 mmole, calibration is conducted with a blank (0 mmole) and 1 mmole standard for convenience. Values obtained between 1 and 2 mmole are still considered valid even though they lie outside the range in which the instrument is calibrated.
8.4.1.1 Blank Reading (0 mmole) - Insert the combination electrode of the voltammetric analyzer into the cleaning solution, remove, and rub dry the bottom electrode surface with a nonabrasive cloth or paper towel. Insert the combination electrode into the prepared blank solution (with minimal delay after preparation) and perform the voltammetric analysis (see 5.1) for liberated iodine. Record the reading. Remove the combination electrode from the blank solution, and rub dry the bottom surface of the electrode. Run at least three tests of the prepared blank to ensure the blank value has leveled off. Complete the blank determinations within 3 min of mixing the reagents.
8.4.1.2 Standard Reading (1 mmole) - Insert the combination electrode of the voltammetric analyzer into the cleaning solution, remove, and rub dry the bottom electrode surface with a nonabrasive cloth or paper towel. Insert the combination electrode into the prepared standard solution (with minimal delay after preparation) and perform the voltammetric analysis (see 5.1) for liberated iodine. Record the reading. Remove the combination electrode from the standard solution, and rub dry the bottom surface of the electrode. Run at least three tests of the standard to ensure the value is stable and repeatable. Complete the standard determinations within 3 min of mixing reagents.
8.4.2 Calibration Frequency - Recalibration with freshly prepared blank and standard solutions should be performed after a set of samples has been tested at one time, with a ten sample maximum within that set.
8.5 Sample Analysis:
8.5.1 Volume Selection - Select the appropriate volume of sample from the following table. If the hydroperoxide value is unknown, use 1 mL of sample. If the determined hydroperoxide value is below 0.1 or above 2 mmole, repeat the analysis after selecting the appropriate volume of sample from the following table.
8.5.2 Sample Preparation - Transfer the sample into a 5-mL glass vial. (Use a 10-mL glass vial if sample volume is above 3 mL.) In succession, transfer 1 mL of acetic acid solution and 0.2 mL of KI solution into the vial, cap the vial, and shake for 20 s, using a vortex mixer. Pipette 1 mL of KCl solution into the vial, cap the vial, and shake gently by hand for 2 s. Let the vial stand undisturbed for 10 s, allowing two layers to form. Use an appropriate size pipette to transfer a volume of test specimen from the lower (aqueous) layer into a second, clean vial. Perform each sample analysis (see 8.5.3) within 3 min of mixing reagents. (The transfers can be accommodated using pipettes or other suitable means).
8.5.3 Sample Analysis - Insert the combination electrode of the voltammetric analyzer into the cleaning solution, remove, and rub dry the bottom electrode surface with a nonabrasive cloth or paper towel. Insert the combination electrode into the prepared sample solution (the aqueous layer pipetted into a second vial) and perform the voltammetric analysis (see 5.1) for liberated iodine. Record the reading. Remove the electrode from the sample solution, wipe off the sides and bottom surface of the electrode, insert the electrode into the cleaning solution, and rub dry the bottom surface of the electrode with a nonabrasive cloth or paper towel.