ASTM D5705 Test Method for Measurement of Hydrogen Sulfide in the Vapor Phase Above Residual Fuel Oils
10. Procedure
10.1 Let each filled sample container sit at room temperature for at least 1 h, transfer part of its contents to an empty 1 L test bottle such that it is filled 50 % +/- 5 volume % with the sample. Discard the remaining contents of the sample container in compliance with applicable laws. A single test is to be performed on material from an individual sample container.
10.2 Insert a nitrogen purge line outlet to within about 13 mm above the fuel surface. Nitrogen purge at 2 L/min for 30 s the headspace above the test sample to displace air and water vapor. Minimize the time the bottle is open to avoid further loss of sample vapors. Close the test bottle opening (gas tight) with a cork stopper fitted with a dial thermometer (Fig. 1(a)) immediately after nitrogen purging.
10.3 Place each test bottle with sample in an oven or a water bath, set at 60 °C +/- 1 °C, until the sample temperature reaches 60 °C +/- 1 °C. Keep the sample in the oven or bath for a minimum of 30 min, which includes the time for the sample to reach 60 °C.
NOTE 5 - If the sample temperature does not reach 60 °C, low results will be obtained for the H2S concentration. If the temperature exceeds 60 °C, high results will be obtained for the H2S concentration.
10.4 While the sample is heating, place an unbroken length-of-stain detector tube in the hand-operated pump and test the pump for leaks. Consult the manufacturer's instructions for leak check procedure details and for maintenance instructions if leaks are detected. The leak check typically takes 1 min. 10.5 Remove the test bottle from the oven and place it in the four-prong clamp of the shaker. Shake at 3.67 s(-1) +/- 0.08 s(-1) (220 r/min +/- 5 r/min (revolutions per minute)) for 3 min +/- 1 s to achieve H 2 S equilibrium between the liquid and the vapor phase.
10.6 Rest the test bottle on a flat surface, remove the stopper with the dial thermometer, and immediately seal the top of the bottle with aluminum foil.
10.7 Select a detector tube with a range that best encompasses the expected H2S concentration. Reading accuracy is improved when the stain length extends into the upper half of the calibration scale.
10.8 Break off the tube tips and insert the tube into the pump, observing the flow direction indication on the tube. Insert the tube through the aluminum foil on the test bottle. Rest the pump on top of the test bottle with the detector tube only contacting the sample's vapor phase. Do not allow the detector tube to contact the liquid, see Fig. 1(b). Use one full compression stroke.
10.9 Remove the detector tube after complete decompression of the pump and immediately read the H2S concentration from the tube's calibration scale or from the charts provided in the box of tubes. Read the tube at the maximum point of the stain. If channeling has occurred (non-uniform stain length), read the maximum and minimum stain lengths and average the two readings. (Warning - If the calibration scale is not printed directly on the detector tube, be certain that any separate calibration chart is the proper match for the tube in use to avoid incorrect results.)
10.10 If the calibration scale specifies more than one stroke, correct the reading as below:
Ccor = C x S
where:
Ccor = the corrected hydrogen sulfide concentration in micromoles per mole (ppm v/v),
C = the reading from the detector tube in micromoles per mole (ppm v/v), and
S = the specified number of strokes.
NOTE 6 - If the test is being conducted at an altitude above 610 m, corrections for barometric pressure are significant. In this case, correct the reading as below:
Ccor = C x 101.325/P
where:
Ccor = the corrected hydrogen sulfide concentration in micromoles per mole (ppm v/v),
C = the reading from the detector tube in micromoles per mole (ppm v/v), and
P = the barometric pressure in kilopascals.
10.11 If the detector tube reading is over- or under-ranged, take another detector tube of a different range and test a second sample of the fuel oil. Do not repeat testing on a previously tested sample or reuse detector tubes. Continue the testing using different ranged detector tubes and new samples until either the reading is on-scale or less than 5 µmol/mol (5 ppm v/v).
10.12 After obtaining a satisfactory first result, repeat the test with another sample of the same fuel oil and a fresh detector tube.
10.13 Record the raw readings, the readings corrected for number of strokes, the readings corrected for barometric pressure, and the test temperature.
