ASTM D5305 Test Method for Determination of Ethyl Mercaptan in LP-Gas Vapor
9. Procedure
9.1 Select the tube range that includes the expected concentration of ethyl mercaptan present in the sample. Reading accuracy is improved when the stain extends at least one-half of the tube length. Consider multiple strokes or a lower range tube, or both, to achieve this length of stain.
9.2 Break off both tips of the glass stain tube and insert the outlet of the tube (indicated by arrow in direction of flow) snugly into the pump head. Temperature of tube shall be maintained in the 0 to 40°C range throughout the test.
9.3 Insert the detector tube well into the gas sampling chamber through the tube access and vent (Vent C).
9.4 Operate the pump to draw a measured amount of sample through the detector tube. Within any limits set by the manufacturer's instructions, use multiple strokes to achieve a stain extending to approximately one-half the tube length.
9.5 Remove the tube from the pump and follow the manufacturer's instructions if further handling of the tube is necessary.
9.6 Within 30 seconds, read the concentration of ethyl mercaptan from graduations on the tube or from charts supplied with the tube. The scale reading nearest the end of the stain is taken as the appropriate scale reading.
10. Interpretation of Results
10.1 If the number of pump strokes used is different from the number specified by the manufacturer, apply a correction as follows:
corrected ethyl mercaptan concentration = scale reading x (specified strokes/actual strokes)
10.2 Some detector tubes that may be used in this test method may be calibrated for other mercaptans in milligrams per cubic metre (mg/m3). Perform the conversion from mg/m3 of t-butyl mercaptan to ppmv of ethyl mercaptan as documented in Annex A1.
10.3 Correct the reading for barometric pressure, especially at high altitudes. For details of this correction, see Annex A1.
10.4 Readings of concentrations below 5 ppmv may not be reliable, and may warrant further investigation. (See Appendix X2.)
NOTE 2 - This test method is a direct measure of the concentration of ethyl mercaptan in the vapor phase of LP-gas. If the temperature of the system is known, results can be used to obtain an approximation of the concentration of ethyl mercaptan in the liquid phase. (See Appendix X1.)
