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
5. Apparatus
5.1 Furnace - An electric furnace held at a temperature (1075 ± 25°C) sufficient to pyrolyze the entire sample and oxidize sulfur to SO2.

5.2 Combustion Tube - A quartz combustion tube constructed to allow the direct injection of the sample into the heated oxidation zone of the furnace. The combustion tube shall have side arms for the introduction of oxygen and carrier gas. The oxidation section shall be large enough (see Fig. 1) to ensure complete combustion of the sample (see 11.3). Fig. 1 depicts a typical combustion tube. Other configurations are acceptable when precision is not degraded.

5.3 Flow Control - The apparatus shall be equipped with flow controllers capable of maintaining a constant supply of oxygen and carrier gas at the specified rates.

5.4 Drier Tube - The apparatus shall be equipped with a mechanism for the removal of water vapor formed during sample combustion. This can be accomplished with a membrane drying tube, or a permeation dryer that utilizes a selective capillary action for water removal.

5.5 UV Fluorescence Detector - A quantitative detector capable of measuring light emitted from the fluorescence of sulfur dioxide by UV light.

5.6 Sample Inlet System - The system provides a heated gas-sampling valve, or a LP gas-sampling valve, or both, with a heated expansion chamber, connected to the inlet of the oxidation area, Fig. 2. The system is swept by an inert carrier gas and shall be capable of allowing the quantitative delivery of the material to be analyzed into the oxidation zone at a controlled and repeatable rate of approximately 30 mL/min. Fig. 3 provides an example.

5.7 Strip Chart Recorder, equivalent electronic data logger, integrator or, recorder (optional).

6. Reagents
6.1 Purity of Reagents - Reagent grade chemicals shall be used in 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 Inert Gas - Argon or helium only, high purity grade (that is, chromatography or zero grade), 99.998 % min purity, moisture 5 mg/kg max. (Warning - Argon or helium may be a compressed gas under high pressure (7.1)).

6.3 Oxygen - High purity (that is chromatography or zero grade), 99.75 % min purity, moisture 5 mg/kg max, dried over molecular sieves. (Warning - Oxygen vigorously accelerates combustion and may be compressed gas under high pressure (7.1)).

6.4 Calibration Standards - Certified calibration standards from commercial sources or calibration gases prepared using certified permeation tube devices are required. Table 1 lists the sulfur source material and diluent matrices used during the inter-laboratory study (Notes 2 and 3).

NOTE 2 - Other sulfur sources and diluent materials may be used if precision and accuracy are not degraded.

NOTE 3 - Calibration standards are typically re-mixed and re-certified on a regular basis depending upon frequency of use and age. These calibration standards may have a useful life of about 6 to 12 months.

6.5 Quality Control (QC) Samples, preferably are portions of one or more gas or LP gas materials that are stable and representative of the samples of interest.