ASTM D2420 Standard Test Method for Hydrogen Sulfide in Liquefied Petroleum (LP) Gases (Lead Acetate Method)
6. Apparatus and Materials
6.1 Apparatus for Detecting Hydrogen Sulfide in Liquefied Petroleum Gas, as shown in Fig. 1 or commercially available apparatus.
6.2 Lead Acetate Test Paper - Commercially available test paper is satisfactory. Alternatively, the test paper may be prepared by dipping strips of smooth filter paper in 5 % aqueous lead acetate solution and removing the excess solution with a clean blotter. The strips of paper shall be approximately 50 mm long and 10 mm wide and contain a 3 mm hole near one end so they will hang freely vertical in the test apparatus.
6.3 Gas Flow Indicator - Capable of measuring flow rates in the range of 2 to 3 L of gas per minute. A wet test meter rotameter and mass flow controller have been found to be suitable.
6.4 Water - Unless otherwise indicated, reference to water shall be understood to mean reagent water that meets the requirements of Type II or III of Specification D1193, or distilled water.
6.5 Tubing - High-pressure connecting tubing to connect the test apparatus to the sample collection point. Internally clean, non-reactive and non-absorptive stainless steel material is recommended, but other materials that safely contain the pressure, resist being cut or torn, and have been tested to be inert relative to the stream being tested may be utilized.
6.5.1 Internal surfaces of sample containers, lines and fittings may be surface coated with an inert material to reduce bare metal surfaces which could react with, or absorb, trace hydrogen sulfide.
6.6 High-Pressure Sample Container, optional - Designed for containing liquefied petroleum gas. An inert surface coating on the inner surface of the container may be used, and is recommended.
7. Sampling
7.1 Collect a representative sample by Practice D1265 using a clean, high-pressure sample container which is inert to hydrogen sulfide.
7.1.1 As an alternative sampling procedure, connect the test apparatus directly to the sample source and perform the test in the field. This method of direct field measurement eliminates any inaccuracy introduced by the sampling procedure or sample container.
7.2 (Warning - Experience has demonstrated that the chemical activity and physical absorptive properties of hydrogen sulfide can cause the concentration of H2S in a liquefied petroleum gas sample to be depleted before analysis, even when the sample is contained in scrupulously clean, stainless steel sample cylinders. Conversely, an increase in sulfide concentration has been found to occur when samples of liquefied petroleum gas containing no hydrogen sulfide are transferred in sample cylinders that have not been properly cleaned and which have been in use with samples containing hydrogen sulfide. This demonstrates that data obtained on samples tested for hydrogen sulfide in the laboratory might not reliably represent the hydrogen sulfide concentration at the sample source.)
