ASTM D6021 Standard Test Method for Measurement of Total Hydrogen Sulfide in Residual Fuels by Multiple Headspace Extraction and Sulfur Specific Detection
11. Procedure
11.1 Remove a sample from refrigerated storage and allow it to stand in the laboratory until it flows freely. A sample can be analyzed as soon as it flows freely. A sample that is still not free flowing after sitting at laboratory ambient for 1 h should be heated gently just until it flows freely. (Warning - At no time should the container temperature be allowed to exceed the temperature of the sample at the time.)
11.2 To avoid possible loss of H2S in the headspace vial by reaction with oxygen, displace the air in the vial with nitrogen prior to transferring a sample into it. Weigh the nitrogen flushed headspace vial and septum seal to the nearest 0.1 mg and then transfer, by any suitable means, as quickly as possible to minimize losses, between 0.05 and 5.0 g of residual fuel oil sample directly into the nitrogen filled headspace vial, and seal the vial immediately with the septum seal to avoid H2S losses PTFE side of the septum in contact with sample. Reweigh the filled headspace vial to the nearest 0.1 mg. Cover the septum seal with an aluminum seal, and crimp the aluminum seal with the hand crimper.
11.3 Place the headspace vial in a 60°C oven for at least 5 min but for no more than 15 min.
11.4 Install an 0.5-mL sample loop if the anticipated H2S concentration is between 1 and 100 ppmw, a 2.5-mL sample loop ifthe anticipated H2S concentration is between 0.1 and 50 ppmw, and a 10-mL sample loop if the anticipated H2S concentration is between 0.01 and 10 ppmw. With Valve 2 in. the load position (see Fig. 1) and Valve 1 closed, evacuate the sample loop by opening Valve 3. When a vacuum of at least -70 kPag is achieved, then close Valve 3.
11.5 Take the headspace vial from the oven, and immediately insert the sampling needle (see Fig. 1) through the septum of the headspace vial containing the residual fuel oil sample.
11.6 Open Valve 1, and let the sample fill the injection loop until a reading of 0 kPa is achieved on the pressure/vacuum gauge. Close Valve 1.
11.7 Place Valve 2 in the Inject position (see Fig. 1) for 10 s to allow the carrier gas to sweep the sample to the H2S analyzer. Return Valve 2 to the load position. Remove sampling needle from the vial. Record reading from the analyzer as reading A1.
11.8 After the injection step, insert a needle connected to a line containing nitrogen at atmospheric pressure into the septum to reestablish atmospheric pressure within the vial.
11.9 Repeat steps 11.3 - 11.9 with the same headspace vial but record the reading from the analyzer as reading A2.
11.10 Repeat steps 11.3 - 11.9 with the same headspace vial but record the reading from the analyzer as reading A3. Two injections are sufficient for the required calculations but three are required to verify the correctness of the multiple extraction procedure.
