This invention relates to a quantitative test for the determination of mercaptan-based odorants in natural, synthetic, L.P. gases and the like.
Conventionally, mercaptan-based odorants are used in gas so that escaping gas can be recognized by members of the general public. These odorants are usually injected into the gas supply prior to the supply entering the distribution facilities of a town or the like and if too much odorant is present, then the slightest leak causes widespread odors thus resulting in unnecessary complaints or reports from the general public. It should be understood mercaptan-based odorants normally used are extremely penetrating in their effect and that it is necessary to maintain the levels within fairly strict limits.
At the present time, there are methods of attempting to assess the amount of mercaptan-based odorant present and the most common method is for the operator to smell the gas. This method is qualitative in nature and depends on the olfactory nerve. It therefore has large variations in readings, depending on the operator, and apart from this inherent error, the operator with a cold is not able to perform the test.
Odorant measuring tubes have been used and this method involves the injection of a known volume of gas by a pump into a tube filled with a reactant which is absorbed on a granular material. The length of the developed stain due to the reaction is a measure of the odorant level, but in actual tests inconsistencies have been observed in the length of the stain which varies with the number of pump strokes and the concentration of odorant. Difficulty has also been observed in measurement of the actual length of the stain as there is no definite demarcation line between the end of the stain and the unstained material.
Titration also gives good quantitative results, but a minimum time of 30 minutes is required to conduct a single test. Furthermore, the apparatus itself is elaborate and requires a relatively high degree of operator skill. It also requires gas pressure greater than those on normal domestic service as the gas has to pass through several fritted glass bubblers.
Laboratory apparatus such as a gas chromatograph can of course be used with good quantitative results, but the size and high cost of the apparatus prohibit its use as a field instrument.