ASTM D7621 Standard Test Method for Determination of Hydrogen Sulfide in Fuel Oils by Rapid Liquid Phase Extraction
8. Sampling and Test Specimen Preparation
8.1 Unless otherwise agreed, samples shall be taken in accordance with Practice D4057.
8.1.1 During sampling operations, care shall be taken to ensure that the integrity of the material is maintained and the possible loss of H2S is kept to a minimum. The precision of this method is critically dependent on the sampling, thermal history, and handling of the test sample.

8.1.2 Collect the sample directly in a suitable clean H2S inert container, of a minimum volume of 500 mL, with an impervious gas-tight closure. Suitable containers include amber glass bottles and epoxy lined containers. The closure aperture shall allow the drawing of a test specimen with the syringe or pipette (see 6.7 and 6.6). Epoxy lined containers shall be visually inspected to ensure that the lining has not been damaged and that the containers are not dented.

8.1.3 To ensure sample integrity fill the sample container to approximately 95 % full and cap immediately.

8.1.4 Where samples are drawn in a manner which does not minimize vapor loss (for example, continuous drip sampling) collect a dedicated sample for H2S determination.

8.1.5 When samples cannot be collected directly into the sample container, transfer the sample from the sampling device into the sample container and ensure that H2S loss is kept to a minimum.

NOTE 3 - The precision has not been determined for smaller volume containers.

8.2 If a dedicated H2S sample cannot be taken, then the H2S measurement shall be the first test carried out on the sample as any additional handling can lead to loss of H2S and low results.

8.3 Take the samples to the laboratory as soon as is practicable after sampling. Test immediately if possible. If samples are not tested immediately, store in a cool place such as a refrigerator (6.4), and analyze within 3 days after sampling.

8.4 Test Specimen Preparation - To minimize the loss of H2S gas, do not homogenize or transfer the sample to another container, and avoid shaking the sample before taking a test specimen.
8.4.1 The sample needs to be flowing freely enough to allow the test specimen to be drawn into the syringe or pipette (see 6.7 and 6.6). A sample that is not free flowing at ambient temperature shall be gently warmed in a water bath or oven (see 6.5) set at a temperature not exceeding 40 ºC.

8.4.2 Samples with viscosities greater than 3000 mm2s(-1) at 50 °C may be tested, but the precision has not been determined.

NOTE 4 - It has been found that samples with a viscosity over 500 mm2s(-1), at 50 °C, usually require warming.

8.4.3 By using a smaller volume of sample it is possible to extend the range of the instrument to over 200 mg/kg but the precision has not been determined.

9. Preparation of Apparatus
9.1 General - Follow the manufacturer's instructions for the correct set up, verification, calibration and operation of the apparatus.

9.2 Location of Apparatus - Use the apparatus under a suitable fume hood or equivalent well-ventilated work space, and vent the gas exit tube to a suitable extractor as the test will release small amounts of H2S gas during test specimen introduction and during the measurement.

9.3 Filters and Tubing:
9.3.1 At the beginning of each test inspect the moisture filter and the liquid trap. Replace the moisture filter if any discoloration is visible.

9.3.2 Replace the tubing that connects to the test vessel if any discoloration is visible.

9.3.3 The inlet air filter shall be replaced every 3 months, or earlier if any discoloration is visible.

9.3.4 Follow the manufacturer's instructions regarding the replacement intervals of the air pump and moisture filters.

9.4 Test Vessel - Before each test ensure that the test vessel and screw cap are clean and dry. Fit the screw cap tightly.

9.5 Liquid Trap - Empty and clean the liquid trap if any liquid or discoloration is visible.

NOTE 5 - Toluene, followed by petroleum ether (60/80), and acetone, are effective in cleaning the test vessel, cap, and liquid trap (see 7.3).

9.6 H2S Detector - Follow the manufacturer's instructions for installing a new calibrated detector and verify the performance immediately afterwards as described in 10.2.3.

9.7 Switch on the apparatus in accordance with the manufacturer's instructions.
9.7.1 Procedure A - After switch on, initiate the vapor phase processor cooling. Confirm that the temperature of the heater jacket is 60.0 °C +/- 1.0 °C and the vapor phase processor is -20.0 °C +/- 2.0 °C. Air purging of the H2S detector commences.

9.7.2 Procedure B: Confirm that the temperature of the heater jacket is 60.0 °C +/- 1.0 °C. Air purging of the H2S detector commences.