ASTM D1552 method for sulfur in petroleum products (High-temperature method)
9. Preparation of Apparatus
9.1 Induction-Type Furnace - Assemble the apparatus according to the instructions furnished by the manufacturer. Purify the oxygen by passing it through (1) H2SO4 (relative density 1.84), (2) Ascarite, and (3) magnesium perchlorate (Mg(ClO4)2) or phosphorus pentoxide (P2O5) (Warning - see 7.4). Connect a rotameter between the purifying train and the furnace. Insert a small glass-wool plug in the upper end of the glass tubing connecting the furnace with the absorber to catch oxides of tin. Connect the exit end of the combustion tube to the absorber with glass tubing, using gum rubber tubing to make connections. Position the absorber so as to make this delivery line as short as possible. Fig. 2 illustrates schematically the assembled apparatus. Adjust the oxygen flow to 1 +/- 0.05 L/min. Add 65 mL of HCl (3 + 197) and 2 mL of starch-iodide solution to the absorber. Add a sufficient amount of the appropriate standard KIO3 solution (Table 1) to produce a faint blue color. This color will serve as the end point for the titration. Adjust the buret to zero. Turn on the furnace filament switch and allow at least 1 min warm-up before running samples (Warning - see 7.4).

9.2 Resistance-Type Furnace - Assemble the apparatus according to the instructions furnished by the manufacturer. Purify the oxygen by passing it through (1) H2SO4 (relative density 1.84), (2) Ascarite, and (3) Mg(ClO4)2 or P2O5 (Warning - see 7.4). Connect a rotameter between the purifying train and the furnace. Fig. 3 illustrates schematically the assembled apparatus. Turn on the current and adjust the furnace control to maintain a constant temperature of 1316 +/- 14°C (2400 +/- 25°F). Adjust the oxygen flow rate to 2 +/- 0.1 L/min. Add 65 mL of HCl (3 +/- 197) and 2 mL of starch-iodide solution to the absorber. Add a few drops of the appropriate standard KIO3 solution (Table 2) to produce a faint blue color. Adjust the buret to zero.

9.3 Resistance-Type Furnace - IR Detection - Assemble and adjust apparatus according to manufacturer's instructions. Initialize microprocessor, check power supplies, set oxygen pressure and flows and set furnace temperature to 1371°C (2500°F).

9.3.1 Condition a fresh anhydrone scrubber with four coal samples when analyzing petroleum coke samples, or with four petroleum product samples that are representative or typical of the sample types to be analyzed.

9.3.2 Calibrate the automatic balance according to manufacturer's instructions.

10. Standardization
10.1 For Iodate Methods:
10.1.1 Determination of Alum Factor:
10.1.1.1 Because these rapid combustion methods involve the reversible reaction 2SO2 + O2 = 2SO3, it is not possible to evolve all the sulfur as SO2. The equilibrium of the reaction is temperature dependent and, in an oxygen atmosphere above 1316°C, about 97 % of the sulfur is present as SO2. To assure that the furnace is in proper adjustment and that its operation produces acceptably high temperature, potassium alum is employed for standardizing the apparatus. Depending on the type of combustion equipment used, proceed as described in Sections 10 to 14 to determine the alum factor. Use 15 mg weighed to +/- 0.1 mg of potassium alum for this determination.

Use the same materials in the determination of the alum and standardization factors as for the unknown samples. For example, V2O5 has a definite effect and should be included if used for unknowns as recommended in the procedure with the resistance-type furnace.

10.1.1.2 Calculate the alum factor as follows:
Alum factor (AF) = (SA x WA)/(100(Va - Vb) x C1)
where:
SA = mass percent sulfur in potassium alum used,
WA = milligrams of potassium alum used,
Va = millilitres of standard KIO3 solution used in determining the alum factor,
Vb = millilitres of standard KIO3 solution used in the blank determination, and
C1 = sulfur equivalent of the standard KIO3 solution used in determining the alum factor, mg/mL.

10.1.1.3 The alum factor should be in the range from 1.02 to 1.08. If values smaller than 1.02 are observed, confirm independently the sulfur content of the alum and the sulfur equivalent of the KIO3 solution before repeating the alum factor determination. If values larger than 1.08 are observed, make adjustments in the equipment in accordance with the manufacturer's recommendation and repeat the alum factor determination.

10.1.2 Determination of Standardization Factor:
10.1.2.1 Because effects such as sample volatility can also affect the relative recovery as SO2 of the sulfur originally present in the sample, it is necessary to determine a standardization factor. Proceed as described in Sections 10 through 14, using an oil sample of similar type to the unknown sample and of accurately known sulfur content.

10.1.2.2 For IR detection, determine and load the microprocessor with the calibration factor for the particular type of sample to be analyzed (lubricating oil, petroleum coke, residual fuel) as recommended by the manufacturer.

10.1.2.3 Calculate the standardization factor as follows:
Standardization factor (Fs) = (Ss x Ws)/(100(Vs - Vb) x C)
where:
Ss = mass percent sulfur in standardization sample used,
Ws = milligrams of standardization sample used,
Vb = millilitres of standard KIO3 solution used in the blank determination,
Vs = millilitres of standard KIO3 solution used in determining the standardization factor, and
C = sulfur equivalent of the standard KIO3 solution used in determining the standardization factor, mg/mL.

10.1.3 Quality Control - Run a suitable analytical quality control sample several times daily. When the observed value lies between acceptable limits on a quality control chart, proceed with sample determinations.

11. Preparation of Coke
11.1 It is assumed that a representative sample has been received for analysis. If the sample of coke received is not dry, it is recommended that the sample be dried prior to grinding.

11.2 Grind and sieve the sample received so as to pass a 60-mesh (250-µm) sieve.

11.3 Dry the sieved material to constant weight at 105 to 110°C.

12. Analysis of Quality Control Samples
12.1 A QC sample shall be analyzed each day samples are analyzed to verify the testing procedure and instrument performance. Additional QC samples may be analyzed. The QC samples shall be treated as outlined in Sections 13, 14, or 15, depending upon the type of furnace set-up used by the lab.

12.2 When QC/Quality Assurance (QA) protocols are already established in the testing facility, these may be used to confirm the reliability of the test result.

12.3 When there is no QC/QA protocol established in the testing facility, Appendix X1 can be used as the QC/QA system.