ASTM D2269 Test Method for Evaluation of White Mineral Oils by Ultraviolet Absorption
6. Apparatus
6.1 Spectrophotometer, equipped to handle liquid samples in 1-cm path length cells. The instrument shall be capable of measuring absorbance with a repeatability of +/-1.0 % or better from an average at the 0.4 absorbance level in the spectral region near 290 nm with a nominal band width of 1 nm or less.
NOTE 1 - For recommended methods of testing spectrophotometers to be used in this test method refer to Practice E 275.
6.2 Fused Quartz Cells, two, having path lengths of 1.00 +/- 0.005 cm, or better. The distance in centimetres does not include the thickness of the cell in which the sample is contained.
6.3 Separatory Funnels, glass-stoppered, 125-mL capacity, equipped with TFE-fluorocarbon stopcocks or other suitable stopcocks that will not contaminate the solvents used.
7. Reagents and Materials
7.1 Solvents :
7.1.1 Normal Hexane - Pure grade, having an ultraviolet light absorbance not exceeding 0.02 down to 260 nm when measured in a 1-cm cell (Warning: Normal hexane is extremely flammable, harmful if inhaled. May produce nerve cell damage.) The purity shall be such that the solvent control as defined in 8.3 shall have an absorbance curve compared to water showing no extraneous impurity peaks and no absorbance exceeding that of dimethyl sulfoxide compared to water at any wavelength in the range 260 to 350 nm, inclusive.
7.1.2 Spectroscopic 2.2.4-Trimethylpentane (Isooctane) - (Warning: Isooctane is extremely flammable, harmful if inhaled.).
NOTE 2 - For a suitable isooctane and a procedure for preparing spectroscopic solvents from commercially available stocks, see Test Method D1840.
7.1.3 Dimethyl Sulfoxide - For use as spectroscopic solvent (see Note 3) (Warning: Dimethyl sulfoxide is combustible. Also it is rapidly absorbed through skin.) Pure grade, clear, water white, 99.9 % dimethyl sulfoxide, m.p. 18.5°C, with an absorbance curve compared to water not exceeding 1.0 at 264 nm and showing no extraneous impurity peaks in the wavelength range up to 350 nm when measured through a path length of 1 cm.
NOTE 3 - This solvent can be purified by percolation through a 1.2-m column of type CAL 1.68 by 0.420 mm (12 by 40 mesh) activated charcoal. The column is 25 mm in diameter, drawn to 6.4 mm in diameter at the bottom and has a reservoir at the top for containing the liquid. Glass wool is placed in the bottom of the column, and about 13 mm of 0.707 to 0.074 (25 to 200 mesh) or 0.0149 to 0.074 (100 to 200 mesh) silica gel is placed on top of it. The column is filled with activated charcoal and the spectroscopic solvent poured into the reservoir and allowed to percolate through the charcoal at atmospheric pressure. The purified solvent is collected at the bottom of the column and stored in glass-stoppered bottles as it is very hygroscopic and reacts with some metal containers in the presence of air.
7.2 Naphthalene - high-purity, 99+ %.
7.3 Standard Reference Solution - A solution containing 7.0 mg of naphthalene per litre of purified isooctane.
7.4 Standard Reference Spectrum - The absorbance curve obtained by scanning the standard reference solution in the range from 260 to 350 nm against isooctane of the same spectral purity as that used to prepare the standard.
7.5 Standard Reference Absorbance - The absorbance at 275 nm of the standard reference spectrum.
NOTE 4 - This absorbance will be approximately 0.30.
