ASTM D1840 Test Method for Naphthalene Hydrocarbons in Aviation Turbine Fuels
ASTM D1840 Standard Test Method for Naphthalene Hydrocarbons in Aviation Turbine Fuels by Ultraviolet Spectrophotometry
10. Procedure A - Serial Dilution
NOTE 4 - The user may use alternative Procedure B if preferred.
10.1 For recommended techniques, refer to Practices E 169. Check carefully sections on handling and cleaning of cells and glassware, instrument adjustments, and method of absorbance measurement.
10.2 Prepare three dilutions of the sample as follows:
10.2.1 First Dilution - If the sample is more volatile than isooctane, add 10 to 15 mL of spectroscopic isooctane to a clean, dry, glass-stoppered, 25 mL volumetric flask. Weigh out approximately 1 g of sample in the flask, dilute to volume with spectroscopic solvent, and mix thoroughly. If the sample is less volatile than isooctane, weigh out approximately 1 g of sample in the flask, dilute to volume with spectroscopic solvent, and mix thoroughly.
10.2.2 Second Dilution - Pipet 5.00 mL of the first dilution into a 50-mL glass-stoppered volumetric flask, dilute to volume with spectroscopic isooctane, and mix thoroughly.
10.2.3 Third Dilution - Dilute 5.00 mL of second dilution to 50 mL in the same manner as in 10.2.2.
10.3 Measurement of Absorbance - Pipet portions of the third dilution into the sample cell of the spectrophotometer. Cover the cells immediately to prevent transfer of aromatic hydrocarbons from the sample cell to the solvent cell. Check the windows of the absorption cells and make certain they are clean. Measure the absorbance as recommended in Practices E 169. Record the absorbance of the sample as compared to spectroscopic isooctance at 285 nm.
NOTE 5 - The dilution of the sample should be controlled so that absorbance readings fall within a range of 0.2 to 0.8 for maximum reproducibility of results. To accomplish this it may be necessary to use an alternative third dilution than the one specified in 10.2.3, such as 10 mL of the second dilution to 25 mL with solvent.
10.4 Determination of Cell Correction - Measure and record the absorbance of the spectroscopic isooctance-filled sample cell as compared to the spectroscopic isooctance-filled solvent cell.
