ASTM D2420 Standard Test Method for Hydrogen Sulfide in Liquefied Petroleum (LP) Gases (Lead Acetate Method)
8. Procedure
8.1 Connect the test apparatus to the sample source by use of a minimum length of high-pressure tubing (see 6.5).
8.2 Flush the line and apparatus for about 1 min.
8.3 Fill the water bath with warm water (50 °C to 70 °C). Tap water is satisfactory.
8.4 By use of the needle valve, adjust the rate of gas flow to 2.3 +/- 0.2 L/min.
8.5 Immediately, place a single strip of water-moistened lead acetate paper on the hook in the test cylinder so that the paper is held midway between the watchglass and the bottom of the upper stopper.
8.6 Expose the moist paper for exactly 2 min to the gas flow of 2.3 +/- 0.2 L/min. Remove the test paper and proceed as described in Section 10.
9. Interpretation of Results
9.1 Compare the exposed test paper with a moist test paper that has not been exposed.
9.1.1 In the absence of distinct coloration, interpret the result as "negative" ("pass").
9.1.2 If there is a distinct coloration, wait 5 min before interpreting the test results.
9.1.2.1 If, after 5 min, the paper has no distinct coloration, interpret the result as "negative" ("pass").
NOTE 1 - The presence of methyl mercaptan in liquefied petroleum gas gives a distinct yellow stain to the test paper which, however, fades completely in less than 5 min.
9.1.2.2 If, after 5 min, the paper does have a distinct coloration, interpret the result as "positive" ("fail").
NOTE 2 - Concentrations of H2S in LPG of 4 mg/m3 and higher will give a positive result.
