ASTM D6667 Total Volatile Sulfur in Gaseous Hydrocarbons/Liquefied Petroleum Gases
ASTM D6667 Standard Test Method for Determination of Total Volatile Sulfur in Gaseous Hydrocarbons and Liquefied Petroleum Gases by Ultraviolet Fluorescence
7. Hazards
7.1 High temperature, flammable hydrocarbons, and gases under high pressures occur in the test method. Use materials that are rated for containing these pressurized hydrocarbons in all sample containers and sample transfer apparatus. Exercise extra care when using flammable materials near the oxidative furnace.
8. Sampling
8.1 Obtain a sample in accordance with Practices F 307, D1265, D3700, D5287, or GPA-2174 or GPA-2166. Analyze samples as soon as possible after taking from bulk supplies to prevent loss of sulfur or contamination due to exposure or contact with sample containers.
8.2 If the sample is not used immediately, then thoroughly mix it in its container prior to taking a test specimen. The use of segregated or specially treated sample containers can help reduce sample cross-contamination and improve sample stability.
9. Preparation of Apparatus
9.1 Assemble and check the apparatus for leaks according to manufacturer's instructions.
9.2 Typical apparatus adjustments and conditions are listed in Table 2.
9.3 Adjust instrument sensitivity and baseline stability and perform instrument-blanking procedures following manufacturer's guidelines.
10. Calibration and Standardization
10.1 Consult Table 3 and select a calibration range based on the anticipated sulfur concentrations present in samples to be analyzed, preferably using a sulfur compound and a diluent type representative of the samples to be analyzed (Note 4). Table 3 is representative of typical ranges, but narrower ranges than those indicated may be used if desired. However, the method precision using narrower ranges than those indicated has not been determined. Ensure the standards used for calibration bracket the concentrations of the samples being analyzed.
NOTE 4 - The number of standards used per curve may vary.
10.2 With the sample valve in the load position, connect the pressurized sample container to the sample valve of the sample inlet system.
10.3 Obtain a quantitative measurement of the injected material by filling the sample loop of the sample valve system for the matrix being analyzed (see Table 2) (Notes 5 and 6).
NOTE 5 - Injection of a constant or similar sample size for all materials analyzed in a selected operating range promotes consistent combustion conditions and may simplify result calculations.
NOTE 6 - An automatic sample transfer and injection device may be used.
10.3.1 Flush the sample loop with sufficient calibrant to assure that the material to be injected is representative.
10.3.2 For LPG samples, if bubbles are present in the viewable portion of the liquid column, flush the sample loop to introduce a new liquid-full sample portion.
10.4 Start the analyzer and inject the calibration material according to the manufacturer's instructions.
10.5 Calibrate the instrument using one of the following techniques.
10.5.1 Multi-point Calibration:
10.5.1.1 When the apparatus features an internal self-calibration routine, analyze the calibration standards and blank three times using the procedures described in 10.2-10.4.
10.5.1.2 Calibrate the analyzer according to the manufacturer's instructions to yield sulfur concentration (see Section 13). This curve is typically linear and system performance shall be checked at least once per day, each day of use. (Note 7).
NOTE 7 - Other calibration curve techniques may be used when accuracy and precision are not degraded. The frequency of calibration may be determined by the use of quality control charts or other quality assurance/quality control techniques.
10.5.2 One-point Calibration:
10.5.2.1 Utilize a calibration standard (6.4) with a sulfur content close to that of the samples to be analyzed (±25 % max.).
10.5.2.2 Follow the instrument manufacturer's instructions to establish an instrument zero (instrument blank) by conducting an analysis run without injection of the calibration standard.
10.5.2.3 Perform measurements of the calibration standard a minimum of three times.
10.5.2.4 Calculate a calibration factor K, in counts per nanogram of sulfur (counts/ng S) as described in 12.2.
