## 1 Introduction  
Hydrogen vehicles are currently commercially available from, or in development by, many manufacturers [1]. With regards to performance, fuelling time and range, these vehicles are nowadays comparable to conventional engines and have one major advantage: they only produce water in the exhaust. The implementation of these vehicles into the consumer market is necessary to help Europe meet the challenging targets for lowering carbon dioxide levels. However, the implementation of these vehicles requires the development of a sizable hydrogen fuelling infrastructure. There are several methods currently used to produce hydrogen for use at fuelling stations. These methods include the electrolysis of water, the steam methane reforming (of natural gas or biogas) and the chloralkali process. Depending on the methods, different impurities that may be present in the final product have negative and sometimes irreversible effects on the vehicle's fuel cell. Therefore, the industry has developed specifications to ensure that these impurities will not impair the operations; the ISO 14687-2:2012 [2] standard (currently under revision) and EN 17124:2018 [3]. These standards set requirements for purity of hydrogen provided by the refuelling stations; no laboratory can however currently perform all of these measurements under accreditation. The specifications in these standards cover a wide range of impurities (13 gaseous species and particles) and include challenging measurements, mainly due to the very low levels of the required detection limits and the need for \"total\" measurements (total hydrocarbons, total sulphur compounds, halogenated compounds). Furthermore, erroneous results can arise from the use of an inappropriate sampling method or from choosing the wrong sampling container. Currently, the methods used for sampling hydrogen gas and particulates from a refuelling station have not been verified to ensure that the sample is representative of the hydrogen at the station. Additionally, the sampling containers used for transporting the gas and particulate samples to the analytical laboratories must be tested to ensure that the sample remains stable during transport. For example, if impurities were to absorb onto the surfaces of the sampling vessels, a \"dirty\" hydrogen could appear to be sufficiently pure during quality assurance checks. A total compounds family usually covers a large number of species having rather different physical properties and the identification of all species is almost impossible in routine analysis. Quantification is mainly done after conversion of the compounds into one species. Interferences or compounds that cannot be converted efficiently may lead to biased results. However, only a few impurities per family may actually be present in the hydrogen. Defining the compounds that are the most likely to be present must be done by a speciation method. As most of the compounds belonging to the species are organic, sorbent tubes could be used to sample hydrogen. By using the right sorbent and the adequate sampling volume, organic impurities belonging to hydrocarbons, halogenated compounds and sulphur compounds will be trapped and retained on the sorbent while the hydrogen will pass through. This will lead to an enrichment of the targeted compounds enabling challenging detection limits to be attained. Recently, a review [4] of publicly available purity analyses of real samples of hydrogen was performed as part of the EMPIR project (European Metrology Programme for Innovation and Research), \"MetroHyVe\" [5]. Totally, 32 hydrogen purity reports [6; 7; 8] from more than 20 different stations were reviewed, focusing on \"total\" species. For hydrocarbons, methane, ethane, acetone were the most common impurities in the hydrogen (present in more than 10 samples). Ethanol, isopropyl alcohol and propane were also found in several samples (in more than 5 samples). Finally, heptane, cyclohexane, n-butane, isobutane, octane and decene were found in a few samples (between 1 to 5 samples).