ASTM F1398-93(2012)

1.3.1 This test method is limited by the sensitivity of current instrumentation, as well as by the response time of the instrumentation. This test method is not intended to be used for components larger than 12.7-mm (¹/₂-in.) outside diameter nominal size. This test method could be applied to larger components; however, the stated volumetric flow rate may not provide adequate mixing to ensure a representative sample. Higher flow rates may improve the mixing but excessively dilute the sample.

1.3.2 Different instrumental methods (such as flame ionization detector (FID), mass spectrometer (MS)) will yield total hydrocarbon (THC) levels that are not comparable due to different sensitivities to different molecular species. Hydrocarbon contaminants of high-purity gas distribution systems can be subdivided into two general categories: ( 1) noncondensable hydrocarbons (<C₄), that are present due to difficulty of removal and relative atmospheric abundance, and (1.3.3 Because of the tremendous disparity of hydrocarbon species, it is suggested that direct comparisons be made only among data gathered using the same detection method.

1.3.4 This test method is intended for use by operators who understand the use of the apparatus at a level equivalent to six months of experience.