ASTM D1552 method for sulfur in petroleum products (High-temperature method)
6. Apparatus
6.1 Combustion and Iodate Detection System:
6.1.1 Furnaces - Two major types are available, the primary difference being the manner in which the necessary high temperatures are obtained. These two types are as follows:
6.1.1.1 Induction Type, which depends upon the high-frequency electrical induction method of heating. This assembly shall be capable of attaining a temperature of at least 1482°C (2700°F) in the sample combustion zone, under the conditions set forth in 9.1 and shall be equipped with an additional induction coil located above the combustion zone, substantially as shown in Fig. 1.

6.1.1.2 The furnace work coil should have a minimum output of 500 W; the minimum input rating of the furnace must be 1000 W. With the correct amount of iron chips, weighed to +/- 0.05 g, the maximum plate current will be between 350 and 450 mA. (Warning - This type of furnace is capable of inflicting high frequency burns and high-voltage shocks. In addition to other precautions, maintain all guards properly.) (Warning - Disconnect the furnace from the power line whenever electrical repairs or adjustments are made.)

6.1.1.3 Resistance Type, capable of maintaining a temperature of at least 1371°C (2500°F).

6.1.2 Absorber, as described in Test Method D1266.

NOTE 1 - Also suitable for use with either type of furnace is an automatic titrator, specifically designed for iodometry. This combines the functions of absorption and titration to a predetermined end point.

6.1.3 Buret, standard 25-mL or automatic types available from the manufacturers of the specific combustion units, are suitable (Note 1).

6.2 Combustion and IR Detection System, comprised of automatic balance, oxygen flow controls, drying tubes, combustion furnace, infrared detector and microprocessor. The furnace shall be capable of maintaining a nominal operating temperature of 1350°C (2460°F).

6.3 Miscellaneous Apparatus - Specific combustion assemblies require additional equipment such as crucibles, combustion boats, crucible lids, boat pushers, separator disks, combustion tubes, sample inserters, oxygen flow indicator, and oxygen drying trains. The additional equipment required is dependent on the type of furnace used and is available from the manufacturer of the specific combustion unit. To attain the lower sulfur concentration given in Section 1, the ceramics used with the induction furnace assembly shall be ignited in a muffle furnace at 1371°C (2500°F) for at least 4 h before use.

6.4 Sieve, 60-mesh (250-mm).

7. Reagents and Materials
7.1 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.

7.2 Purity of Water - Unless otherwise indicated, references to water shall be understood to mean reagent water as defined by Type II or III of Specification D1193.

7.3 Alundum (Al2O3) or Magnesium Oxide (Com-Aid).

7.4 Anhydrone (Magnesium Perchlorate). (Warning - In addition to other precautions, handle magnesium perchlorate with care. Avoid contacting it with acid and organic materials. Reactions with fuel may be violent.)

7.5 Hydrochloric Acid (3 + 197) - Dilute 30 mL of concentrated hydrochloric acid (HCl, relative density 1.19) to 2 L with water. (Warning - Poison. Corrosive. May be fatal if swallowed. Liquid and vapor cause severe burns.)

7.6 Oxygen (Extra Dry) - The oxygen shall be at least 99.5 % pure and show no detectable sulfur by blank determination. (Warning - Oxygen vigorously accelerates combustion.)

7.7 Phosphorus Pentoxide - (P2O5).

7.8 Potassium Alum (Aluminum Potassium Sulfate).

7.9 Potassium Iodate, Standard Solution (0.06238 N), 1 mL of this solution is equivalent to 1 mg S) - Dissolve 2.225 g of potassium iodate (KIO3) that has been dried at about 180°C to constant weight, in water and dilute to 1 L. Thoroughly mix the solution.

7.10 Potassium Iodate, Standard Solution (0.006238 N), 1 mL of this solution is equivalent to 0.1 mg S) - Measure exactly 100 mL of KIO3 solution (0.06238 N) into a 1–L volumetric flask, and dilute to volume with water. Thoroughly mix the solution.

7.11 Potassium Iodate, Standard Solution (0.01248 N), 1 mL of this solution is equivalent to 0.2 mg S) - Measure exactly 200 mL of KIO3 solution (0.06238 N) into a 1-L volumetric flask and dilute to volume with water. Thoroughly mix the solution.

7.12 Ascarite, 8 to 20 mesh.

7.13 Special Materials for Induction-Type Furnaces:
7.13.1 Tin (20 to 30-mesh).

7.13.2 Iron-Chip Accelerator having a sulfur content of not more than 0.005 mass %.

7.14 Standard Sample - Potassium alum (AlK(SO4)2•12H2O).

7.15 Starch-Iodide Solution - Make a paste by adding 9 g of soluble starch to 15 mL of water. Add this mixture, with stirring, to 500 mL of boiling water. Cool the mixture, add 15 g of potassium iodide (KI), and dilute to 1 L with water.

7.16 Sulfuric Acid (relative density 1.84) - Concentrated sulfuric acid (H2SO4). (Warning - Poison. Corrosive. Strong oxidizer.)

7.17 Vanadium Pentoxide, anhydrous, powdered V2O5.

7.18 Quality Control (QC) Sample(s) , preferably are portions of one or more petroleum products that are stable and representative of the samples of interest. These QC samples can be used to check the validity of the testing process and performance of the instrument as described in Section 12.

8. Sampling
8.1 Take samples in accordance with the instructions in Practice D4057.