## 2 Methods
### Chemicals and Gas Mixtures
#### 2.3.3. Sulphur Compounds  
A static gas mixture was prepared in an aluminium cylinder containing all the sulphur compounds listed in Table 3. As an internal standard, n-hexane was added. For the preparation of the static gas mixture, a liquid mixture containing CS\({}_{2}\), T-BM, THT and hexane (C6) was prepared using a Liquid Mixture Robot (LMR) developed at VSL. The LMR is equipped with a Multi-Purpose Sampler (MPS), a multifunctional autosampler and sample preparation robot (from Gerstel), an analytical balance (from Mettler), and a system for controlling the MPS and the balance. The LMR allows the automatic preparation of liquid mixtures containing up to 20 individual components. The individual components were added in decreasing order according to their boiling points. The liquid mixture obtained was injected with a syringe into an evacuated cylinder, treated with an Alphatech(r) H\({}_{2}\)S coating, then vaporized and diluted with nitrogen, to obtain a mother mixture. The mother mixture was further diluted and COS, H\({}_{2}\)S and CH\({}_{4}\)S were added to obtain the end mixture. The gas mixture preparation was performed by static gravimetry according to ISO 6142-1 [24]. The composition of the final mixture (VSL162904) used for the short-term stability tests is given in Table 3.  
According to ISO 14687-2 [2] the threshold for total sulphur compounds in hydrogen is 0.004 mol/mol (4 nmol/mol). This value is based on requirements from the Proton Exchange Fuel cell producers and the detection limits of available instruments and test methods. To reach lower mole fraction, the static gas mixture was dynamically diluted with N\({}_{2}\) using thermal mass-flow controllers according to ISO 6145-7 [25]. Dilutions from approximately 400 nmol/mol per sulphide in the static gas mixture to approximately 100 and 20 nmol/mol per sulphide in the dynamic gas mixture were produced for the short-test stability (Table 4). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Components** & \begin{tabular}{c} **Mole Fraction before** \\ **Dilution (nmol/mol)** \\ \end{tabular} & \
\begin{tabular}{c} **Mole Fraction after** \\ **Dilution (nmol/mol)** \\ \end{tabular} &
\begin{tabular}{c} **Expanded Uncertainty** \\ **(nmol/mol) (k = 2)** \\ \end{tabular} \\ \hline Chloromethane & 5130 & 51.30 & 3.08 \\ Vinyl chloride & 5009 & 50.09 & 3.51 \\ Ethane, 1,1,2-trichloro-1,2,2-trifluor & 4768 & 47.68 & 2.86 \\ Dichoromethane & 5005 & 50.05 & 3.00 \\
12-dichlorethylene & 5173 & 51.73 & 3.10 \\ Chloroform & 5196 & 51.96 & 3.12 \\ Trichoethylene & 5276 & 52.76 & 3.17 \\
12-dichloropopane & 5261 & 52.61 & 3.16 \\
112-trichloroethane & 6951 & 69.51 & 4.17 \\ Tetrachloroethylene & 5242 & 52.42 & 3.15 \\ Tetrahexafluorobutane & 3030 & 30.30 & 2.12 \\ Dichorobenzene & 1005 & 10.05 & 0.70 \\ \hline \hline \end{tabular} Subsequently, a volume of 240 mL of this gas mixture was transferred onto the sorbent tubes on the starting day (D0). All the tubes were then stored in the fridge (+4 °C) prior to analysis.  
\end{table} 
Table 2: Composition of the gas mixture used for halogenated hydrocarbons. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Component** & \
\begin{tabular}{c} **Mole Fraction (nmol/mol)** \\ \end{tabular} &
\begin{tabular}{c} **Expanded Uncertainty** \\ **(nmol/mol) (k = 2)** \\ \end{tabular} \\ \hline H\({}_{2}\)S & 392.66 & 0.19 \\ CH\({}_{4}\)S & 395.4 & 0.4 \\ COS & 392.19 & 0.32 \\ C6 \({}^{*}\) & 434.4 & 0.5 \\ CS\({}_{2}\) & 408.1 & 0.5 \\ THT & 427.0 & 0.5 \\ T-BM & 389.9 & 0.6 \\ \hline \hline \end{tabular} \({}^{*}\) Internal standard.  
\end{table} 
Table 3: Composition sulphur gas mixture VSL162904. The dynamically obtained gas mixtures were transferred onto sorbents using a specially designed sampling manifold. The manifold is equipped with mass-flow controllers (MPCs) and 3-way valves to allow the simultaneous sampling of 12 sorbent tubes.