ASTM D5705 Test Method for Measurement of Hydrogen Sulfide in the Vapor Phase Above Residual Fuel Oils
7. Apparatus
7.1 Shaker, a bench-top orbital shaker and platform equipped with a four-prong clamp to hold 1 L Boston round-bottom glass bottles and capable of operation at 3.67 s(-1) +/- 0.08 s(-1) (220 r/min +/- 5 r/min (revolutions per minute)).
NOTE 3 - An orbital shaker with an orbit of 19 mm has been found to be suitable.
7.2 Timer, capable of measuring from 1 s to 30 min at second intervals.
7.3 Stopper with Temperature Measuring Device, a No. 2 cork stopper with a temperature measuring devices inserted through it that is capable of accurately measuring the temperature of the sample at 60 °C +/- 1 °C as required in the procedure and extending at least 25 mm into the residual fuel but no closer than 25 mm from the bottom of a test bottle (see Fig. 1(a)). A dial thermometer having a range of -18 °C to 82 °C and a 200 mm stem has been found suitable to use.
7.4 Oven or Water Bath, capable of heating the fuel oil samples to 60 °C +/- 1 °C.
7.5 Detector Tube Pump, a hand-operated piston or bellows-type (Fig. 1(b)) pump with a capacity of 100 cm3 +/- 5 cm3 per stroke. It must be specifically designed for use with detector tubes. (Warning - A detector tube and pump together form a unit and must be used as such. Each manufacturer calibrates detector tubes to match the flow characteristics of its specific pump. Crossing brands of pumps and tubes is not permitted, as considerable loss of system accuracy is likely to occur.)
8. Reagents and Materials
8.1 Containers - Both sample and test containers are composed of H2S-inert material such as 1 L size (clear Boston round-bottom) glass bottles with screw caps. The bottles are clean and dry. Mark test containers at the 50 % volume level by using a ruler. (Warning - Hydrogen sulfide reacts with metal surfaces and is easily oxidized, which depletes its concentration and gives false low test results. Containers such as epoxy-lacquered cans are suitable for sample collection. Alternative containers must give equivalent results to those obtained by using glass.)
8.2 Length-of-Stain Detector Tube and Calibration Scale, a sealed glass tube with breakoff tips sized to fit the tube holder of the detector tube pump. The reagent layer inside the tube, typically a silica gel substrate coated with the active chemicals, must be specific for hydrogen sulfide and must produce a distinct color change when exposed to a sample of gas containing hydrogen sulfide. Any substances known to interfere must be listed in the instructions accompanying the tubes. A calibration scale should be marked directly on the tube, or other markings that provide for easy interpretation (reading) of hydrogen sulfide content from a separate calibration scale should be supplied with the tubes. The calibration scale shall correlate H2S concentration to the length of the color stain. Annex A1 provides additional information. Shelf life of the detector tubes must be a minimum of two years from the date of manufacture, when stored according to the manufacturer's recommendations.
9. Sampling
9.1 The sampling of residual fuel oils is done according to Practice D4057 for the sampling of storage tanks, ships, or barges. Composite sampling or running samples can be taken; spot samples should be taken from the midpoint or below midpoint of the fuel oil in a storage tank by first sufficiently purging sample transfer lines and then taking single samples where each sample comprises one and only one test. (Warning - Samples taken for this test method shall be dedicated to a single H2S determination and not used for any other purpose, as any additional handling can lead to loss of H2S and thus low results.)
NOTE 4 - Liquid samples taken well into the fuel oil have had less H2S lost by degassing as compared with a fuel oil's surface. Samples taken from well within the fuel oil storage provide material that represents the greatest potential for H2S exposure during fuel oil movements. Hydrogen sulfide is lost by degassing (elevated temperature and mechanical agitation increases H 2 S degassing), oxidation, and absorption on water-wet surfaces.
9.2 Fill at least two 1 L size sample containers with fuel oil. Minimize the headspace of the sample container. Cap immediately and deliver to the testing facility. Test each sample within one to four hours from the time of sampling.
9.3 Sample integrity is extremely important; therefore, sample containers must be composed of inert materials, filled nearly completely with liquid, and capped tightly until tested. Sample handling should be minimized, and rapid testing for H2S is required. Samples can not be stored for later testing as H2S loss may occur by the mechanism described in Note 4.
