ASTM D1266 Test Method for Sulfur in Petroleum Products (Lamp Method)
5. Apparatus
5.1 Absorbers, Chimneys, Lamps, and Spray Traps (Fig. 1), as required are described in detail in Annex A3. The standard flask and burner (Fig. A3.1) as shown is not suitable for burning highly aromatic mixtures without blending. The flask and burner for aromatic samples (Fig. A3.1) permits burning these samples directly without blending and may also be used to burn nonaromatic samples; with this lamp, a second port with control valve in the burner manifold is required.
5.2 Cotton Wicking - Clean, unused, uniform, twisted white cotton yarn of good quality. For the burner to burn aromatic samples use long staple, fine-spun, commercial fine grade.
5.3 Manifold System, consisting of a vacuum manifold with regulating device, valves, and so forth (Fig. 2) and a dual manifold (burner and chimney) supplying a gas mixture of approximately 70 % carbon dioxide (CO2) and 30 % oxygen (O2) at regulated pressures. The vacuum manifold shall be connected to a pump of sufficient capacity to permit a steady gas flow of about 3 L/min through each absorber and to maintain a constant manifold pressure of approximately 40 cm of water below atmospheric. The gas mixture in the chimney manifold shall be maintained at a nearly constant pressure of 1 to 2 cm of water and the burner manifold at approximately 20 cm of water. A suitable arrangement is shown in Fig. 2 and described in Annex A3, but any other similar system can be used. Modifications of the manifold and associated equipment for burning samples in air are shown in Fig. A2.1 and described in Annex A2.
6. Reagents and Materials
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 as defined by Type II or Type III of Specification D1193.
6.3 Carbon Dioxide and Oxygen - The carbon dioxide (CO2) and the oxygen (O2) shall each be at least 99.5 % pure. These gases shall meet the requirements of 9.5.
6.4 Diluent - The diluent used shall have a sulfur content less than 0.001 mass %, be completely miscible with the sample to be analyzed, and permit burning at a moderate rate without smoking. Normal heptane, isooctane, and absolute ethyl alcohol have been found suitable (Note 10).
6.5 Hydrochloric Acid (1 + 10) - Mix 1 volume of concentrated hydrochloric acid (HCl, relative density 1.19) with 10 volumes of water.
6.6 Hydrogen Peroxide Solution (1 + 19) - Mix 1 volume of concentrated hydrogen peroxide (H2O 2, 30 percent) with 19 volumes of water. Store in a dark-colored glass-stoppered bottle.
6.7 Methyl Purple Indicator - Aqueous solution containing approximately 0.1 % active constituent. (Not methyl violet.)
6.8 Sodium Hydroxide Solution (100 g/L) - Dissolve 100 g of sodium hydroxide (NaOH) in water and dilute to 1 L.
6.9 Sodium Hydroxide, Standard Solution (0.05 M) - Dilute 2.8 mL of saturated NaOH solution to 1 L (Note 3), using for this purpose the clear saturated solution decanted after standing long enough to permit any precipitate to settle out. Standardize by titration against standard acid, using the methyl purple indicator. Store in an alkali-resistant glass bottle and protect to minimize contamination by CO2 from the air. Use only pure gum rubber tubing for connections between the storage bottles and burets.
NOTE 3 - The calculation of results can be simplified by adjusting the molarity of the NaOH solution to 0.0624 more or less 0.0001. Then 1 mL of the NaOH solution will be equivalent to 0.0010 g of sulfur. In this case, the factor 16.03M in the calculation (see 12.1) becomes 1.000.
6.10 Quality Control (QC) Sample(s), preferably are portions of one or more liquid petroleum materials or product standards of known sulfur content that were not used in the generation of the instrument calibration curve. These (QC) samples are to be used to check the validity of the testing process as described in Section 12. An ample supply of QC sample material shall be available for the intended period of use, and must be homogeneous and stable under the anticipated storage conditions.
