ASTM D6428 Test Method for Total Sulfur in Liquid Aromatic Hydrocarbons and Their Derivatives by Oxidative Combustion and Electrochemical Detection
9. Hazards
9.1 Consult current OSHA regulations, suppliers' Materials Safety Data Sheets, and local regulations for all materials used in this test method.
9.2 High temperature is employed in this test method. Extra care must be exercised when using flammable materials near the high temperature furnace.
10. Sample Handling
10.1 Collect the samples in accordance with Practice D3437 or Practice D3852 as appropriate.
10.2 To preserve sample integrity (consistency) and prevent the loss of volatile components, which may be in some samples, do not uncover samples any longer than necessary. Analyze samples as soon as possible after taking from the bulk supplies to prevent loss of sulfur or contamination.
10.3 Since this procedure is intended for trace level contamination, care must be taken to ensure the containers used for the sample, the specimen, and the working standards do not alter the sample result.
11. Preparation of Apparatus
11.1 Assemble the apparatus in accordance with manufacturer's instructions.
11.2 Adjust the gas flows and the combustion temperature to the desired operating conditions.
12. Calibration and Standardization
12.1 Prepare a series of calibration standards using a stock solution covering the range of operation as described in 8.6-8.8, and consisting of sulfur type and matrix similar to samples to be analyzed.
12.2 Volumetric measurement of the injected sample can be obtained by filling the syringe to the 80 % level, retracting the plunger so that the lower liquid meniscus falls on the 10 % scale mark, and recording volume ofliquid in the syringe. After the sample has been injected, again retract the plunger so that the lower liquid meniscus falls on the 10 % scale mark, and record the volume of liquid in the syringe. The difference between the two volume readings is the volume of sample injected.
12.3 Alternatively, the sample injection device may be weighed before and after injection to determine the amount of sample injected. This test method provides greater precision than the volume delivery method, provided a balance with a precision of +/- 0.01 mg is used.
12.4 Insert the syringe needle through the inlet septum up to the syringe barrel and inject the sample or standard at a uniform rate of 0.2 to 1.0 µL/s. Rate of injection is dependent on such factors as viscosity, hydrocarbon type, and sulfur concentration. Each user must adopt a method whereby a consistent and uniform injection rate is ensured.
NOTE 9 - For the most consistent injection rate and best analytical results, a constant rate injection system or automatic sampling system may be helpful. Consult manufacturer for recommendations.
NOTE 10 - With direct injection below 2 mg/kg of sulfur, the needle-septum blank may become increasingly important. Error due to this can be avoided by inserting the syringe needle into the hot inlet and allowing the needle-septum blank to dissipate before injecting the sample.
12.5 For the method blank, rinse the syringe thoroughly with the solvent blank, Then inject the same amount of solvent blank as utilized with standards and obtain the reading. Measure the blank a second time and average the results. The solvent blank should contain less than 0.05 mg/kg of sulfur.
12.6 If the system features an automatic calibration procedure, repeat the measurement ofeach calibration standard three times. All calibration points shall be used to construct a calibration curve. System performance shall be checked with suitable calibration standard each day and when changing concentration ranges.
12.7 For those analyzers not equipped with an automatic calibration procedure, construct a standard curve as follows: Repeat the determination of each calibration standard and the blank three times to determine the average net response for each standard. Construct a curve plotting milligrams of sulfur injected versus detector response (integration count). The response curve should be linear and shall be checked at least once per week.
