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
7. Apparatus
7.1 Spectrophotometer, equipped to measure the absorbance of solutions in the spectral region 240 to 300 nm with a spectral slit width of 1 nm or less. Wavelength measurements shall be repeatable and known to be accurate within 0.1 nm or less as measured by mercury emission line at 253.65 nm or the absorption spectrum of either holmium oxide glass at 287.5 nm or holmium oxide solution at 287.1 nm. At the 0.4 absorbance level in the spectral region between 240 and 300 nm, absorbance measurements shall be repeatable within more or less 0.5 % or better. In the absorbance range encompassing 0.2 to 0.8, the photometric accuracy shall not differ by more than more or less 0.5 % of samples whose absorbance has been established by a standardizing laboratory.
7.1.1 Discussion - Many manufacturers provide secondary standards, traceable to NIST primary standards, for checking the wavelength accuracy and photometric accuracy of spectrophotometers. These materials may be used to verify spectrophotometer performance provided that they have been recalibrated periodically as recommended by the manufacturer.
7.2 It shall be initially and thereafter periodically demonstrated that an instrument can be operated in a manner to give test results equivalent to those described in 7.1.
NOTE 1 - For recommended methods of testing spectrophotometers to be used in this test method, refer to Practice E 275. Other preferred alternatives to those in 7.1 are potassium dichromate in perchloric acid (NIST SRM 935 series as described in Practice E 275) for photometric accuracy and a 20 mg/L high (>99 %) purity naphthalene in spectroscopic grade isooctane for wavelength accuracy. The latter has a minor maximum at 285.7 nm. The naphthalene solution shall not be used for photometric accuracy.
7.3 Vitreous Silica Cells, two, having path lengths of 1.00 more or less 0.005 cm.
7.4 Pipets, Class A.
7.5 Lens Paper.
7.6 Balance, capable of taring or weighing 100 g to the nearest 0.0001 g. The balance shall be accurate to more or less 0.0002 g at a 100-g load.
8. Solvents
8.1 Spectroscopic 2,2,4 Trimethyl Pentane (Isooctane). (Warning - Isooctane is extremely flammable, harmful if inhaled.)
NOTE 2 - Spectroscopic-grade isooctane is available commercially. Technical-grade isooctane is a satisfactory base stock for the preparation of spectroscopic solvent. Allow about 4 or 5 L of this material to percolate through a column of activated silica gel (74 µm) 50.8 to 76.2 mm in diameter and 0.6 to 0.9 m in depth. Collect only the portion of the solvent that has a transmission compared to distilled water greater than 90 % over the entire spectral range from 240 to 300 nm. Store in scrupulously clean glass-stoppered bottles and always keep covered. In general it will be best to use a fresh portion of silica gel in preparing a new batch of solvent. However the gel can be reactivated by pouring 500 mL of acetone through the column, draining, drying by suction, and heating the gel in thin layers in an oven at 400°C until white color is restored. Activated silica gel is stored in closed containers.
8.2 Solvents for Cleaning Cells - Acetone or ethyl alcohol, with residue after evaporation no greater than 10 mg/kg. (Warning - Acetone and ethyl alcohol are extremely flammable and can be harmful if inhaled.)
NOTE 3 - The 10 mg/kg is the American Chemical Society (ACS) reagent grade maximum specification. An ACS reagent grade solvent may be used without further testing.
