5.1 Low operating temperature fuel cells such as proton exchange membrane fuel cells (PEM-FC) require high purity hydrogen for maximum material performance and lifetime. Analysis to 0.1 part per million (ppm(v)) concentration of total hydrocarbons (measured as methane) in hydrogen is necessary for ensuring a feed gas of sufficient purity to satisfy fuel cell system needs as defined in SAE J2719 or as specified in regulatory codes.

5.2 Dynamic dilution techniques using highly accurate mass flow controllers can be used with test samples that have total hydrocarbon content exceeding the upper limit of the instrument’s linear range, without the need to recalibrate the instrument using higher levels of calibration standards. The sample can be diluted with a high purity grade of hydrogen (99.999 %, so long as it contains < 0.1 ppm(v) total hydrocarbons) to achieve a result of the total hydrocarbon content by applying the appropriate dilution factor to the result. Samples that contain total hydrocarbon concentrations greater than 1000 ppm(v) may be determined, although results will likey be achieved with reduced precision and should be analyzed by the dilution method.

5.3 Although not intended for application to gases other than hydrogen, techniques within this test method can be applied to other non-hydrocarbon gas samples requiring total hydrocarbon content determination. This can be achieved by using a zero gas and a calibration gas that consist of the same background gas as the actual sample. As an example, for the total hydrocarbon determination of nitrogen, the instrument zero point must be determined with a high purity grade of nitrogen (99.999 % and < 0.1 ppm(v) total hydrocarbons) and the instrument calibration must be done with a certified standard of methane in nitrogen in the appropriate range. This will correct for any interferences caused by the background gas.

1.1 This test method describes a procedure for total hydrocarbons (THC) measurement in hydrogen intended as a fuel for fuel cells on a methane (C1) basis. The determination of total hydrocarbons on a C1 basis is an analytical technique where all of the hydrocarbons are assumed to have the same response as methane. Sensitivity from 0.1 part per million (ppm(v), µmole/mole) up to 1000 parts per million (ppm(v), µmole/mole) concentration are achievable. Higher concentrations can be analyzed using appropriate dilution techniques. This test method can be applied to other gaseous samples requiring analysis of trace constituents provided an assessment of potential interferences has been accomplished.

1.2 This test method is an FID-based hydrocarbon analysis method without the use of separation columns. Therefore, this method does not provide speciation of individual hydrocarbons. Several varieties of instruments are manufactured and can be used for this method.

1.2.1 This method provides a measure of total hydrocarbons “as methane,” because all hydrocarbon species are quantified the same as methane response, which is the sole species used for calibration. Magnitude of the FID response to an atom of carbon is dependent on the chemical environment of this atom in the molecule. This method provides the total hydrocarbon result as if all carbon atoms are from aliphatic, aromatic, olefinic, or acetylenic compounds, where the detector response caused by these atoms are approximately relative to the number of carbon atoms present in the molecule. Other types of molecules, including those containing oxygen or chlorine atoms will respond differently and usually much lower than the corresponding aliphatic hydrocarbon. Therefore other methods (Test Methods D7653, D7892, or equivalent) must be utilized to determine the exact constituents of the total hydrocarbon response determined by this method.

1.3 The proper handling of compressed gas cylinders containing air, nitrogen, hydrogen, or helium requires the use of gas regulators to preclude over-pressurization of any instrument component

1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.