ASTM D6021 Standard Test Method for Measurement of Total Hydrogen Sulfide in Residual Fuels by Multiple Headspace Extraction and Sulfur Specific Detection
6. Apparatus
6.1 A schematic of the headspace sampling system required for this analysis is shown in Fig. 1. It consists of:
6.1.1 Sampling On/Off Valve, with 3.2 mm o.d. connector (Valve 1).

6.1.2 Six-Port External Loop Injection Valve, made with 316 stainless steel, resistant to attack by sulfur compounds and having 3.2 mm o.d. tubing from each port (Valve 2).

6.1.3 Polytetrafluoroethylene (PTFE) Sample Loops, of 0.5, 2.5, and 10 mL are used for H2S content of 1 to 100, 0.1 to 50, and 0.01 to 10 ppmw, respectively.

6.1.4 Pressure/Vacuum Gage, 6.3 mm diameter dial type with range of -100 to 200 kPag, 5 kPa divisions from -100 to 0 and 10 kPa divisions from 0 to 200 kPag.

6.1.5 Vacuum On/Off Valve, 3.2 mm o.d. connector (Valve 3).

6.1.6 Sulfur Selective Detector, any H2S specific detector capable of measuring H2S in the gas from 1 to 10 000 ppmv with a repeatability of +/- 2 % of full scale.

NOTE 3 - Good performance has been obtained with a lead acetate tape detector and a sulfur chemiluminescence detector.

6.1.7 Fluorocarbon Tubing, 0.6 m long by 3.2 mm o.d. to connect components together.

6.2 Vacuum pump, 3.2 mm o.d. outlet, capable of achieving a 0.2 kPa vacuum and with a capacity of 100 mL/min.

6.3 Headspace Oven, capable of operating at 60 +/- 0.5°C with internal dimensions of 30 by 30 by 30 cm. An optional vent line is recommended in case a vial leaks.

6.4 Analytical Balance, sensitivity of 0.01 mg, maximum weight of 250 g.

6.5 Data Handling System, such as electronic integrator or any computer unit that can work with a chromatographic signal.

6.6 If sulfur specific detectors are used instead of an H2S analyzer then a chromatographic system equipped with a suitable column and oven is required to separate H2S from other sulfur compounds (see Test Method D5504).

6.7 Hand Crimper, to crimp 20 mm diameter aluminum seals.

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 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 Acetic Acid Solution - Add 50 mL of glacial acetic acid (CH3COOH) to a 1-L volumetric flask and then add Type II distilled water, as specified in Specification D1193, to the 1-L mark to make a 5 % acetic acid solution.

7.3 Aluminum Seals, 20 mm diameter to seal septas to headspace sample vials.

7.4 Headspace Vials, 30-, 60-, or 120-mL borosilicate glass vials with 20 mm mouth diameter.

7.5 Hydrogen Sulfide Gas Calibration Standard, 1, 10, and 100 µL/L H2S in helium or nitrogen high pressure cylinders (obtain from gas supply company). (Warning - Hydrogen sulfide is an extremely toxic gas.)

7.6 Gases, helium or nitrogen (H2S free), chemically pure grade or purified, as carrier gas to sweep sample into the detector.

7.7 Lead Acetate Sensing Paper - Prepare in accordance with Test Method D2420, using appropriate size strips and drying in an H2S-free environment. Commercially available test paper has been found satisfactory.

NOTE 4 - Reagents from 7.2 and 7.7 are only needed if using an H2S lead acetate tape detector.

7.8 Nuts and Ferrules, Polytetrafluoroethylene (PTFE) and stainless steel (3.2 mm).

7.9 Septas, 20 mm diameter PTFE silicone/fluorocarbon to seal headspace sample vials.

7.10 Side Port Needles, for pressure lock, A-gas series (with reduction union 3.2 mm to 1.6 mm).

7.11 Syringe Needles, common dischargeable (dosing needle).