## 3 Results and Discussion
### Suitability of Sorbent Materials
#### 3.2.3 Sulphur Compounds  
The gas mixture VSL162904 (concentration around 400 nmol/mol for each sulphur compound) was first analysed with GC/MS to verify the composition of the static gas mixture (Figure 7a). The compounds were detected by the mass spectrometer, even though hydrogen sulphide coelutes with carbon dioxide. When analysing the diluted gas mixtures after transfer onto sorbent tubes, hydrogen sulphide and methyl mercaptan could not be detected on either of the three selected sorbent materials (Figure 7b). Furthermore, sulphur dioxide which was not present in the gas mixture was identified; mostly on Carboxen 1003 (much smaller amounts were detected on Tenax TA and Tenax TA/SulfiCarb). A possible explanation for the presence of sulphur dioxide is that sulphur compounds partly react with oxygen when stored on the sorbent materials. Figure 5: Storage stability of halogenated hydrocarbons on TCC. (**a**) for 1,2-dichlorobenzene, 1,2-dichloropropane, 1,1,2-trichloroethane, chloroform; (**b**) for 1,2-dichloroethylene, vinylchloride, for chloromethane, dichloromethane. (**c**) for tetrachlorohexabutane, trichloroethylene, tetrachloroethylene, freon 113. Figure 6: Storage stability of halogenated hydrocarbons on Tenax TA. (**a**) for 1,2-dichlorobenzene, 1,2-dichloropropane, 1,1,2-trichloroethane, chloroform; (**b**) for 1,2-dichloroethylene, vinylchloride, for chloromethane, dichloromethane. (**c**) for tetrachlorohexabutane, trichloroethylene, freon 113. The recovery yields were estimated by calculating the breakthrough of sulphur compounds for all three sorbent materials. To determine this, two tubes were connected in series during loading and both tubes were desorbed and analysed. If the recovery is complete, the first tube should contain the compounds while the second tube should remain clean. The second tube, when using either Tenax TA/SulfiCarb or Carboxen 1003 sorbent materials was observed to be clean (all compounds below detection limit). However, the Tenax TA tubes contained 5% of the total CS\({}_{2}\) and 37% of the total T-BM. Figure 7: (a) Chromatogram analysis of VSL162904 containing approximately 400 nmol/mol per sulphur component (CO2: carbon dioxide, H2S: hydrogen sulphide, COS: carbonyl supplied, CH4S: methyl-mercapan, C6: Hexane, T-BM: tert-butyl-mercapan, THT: tetrahydrothiophene). (b) Chromatogram analysis of the sulphur compounds (at \(\sim\)100 nmol/mol) on Carboxen 1003. To prevent breakthrough shorter loading times could be used however, loading times less than 10 min are not recommended because they lead to less accurate results. The desorption efficiency at 275 \({}^{\circ}\)C was determined by analysing the tubes twice, to determine if there were traces of components left on the tubes after the first analysis. As the response for COS relative to C6 was very low it was difficult to determine the desorption efficiency for this compound. Only hexane was found on the Carboxen 1003 tubes in the second analysis. Therefore, the desorption temperature was then performed at 300 \({}^{\circ}\)C. During a second control of the desorption efficiency, no hexane was found. Five tubes for each sorbent material, and 1 or 2 blanks were analysed on 6 different days during a period of 14 days to determine the short-term stability. During these 14 days, the sorbent tubes were stored in the laboratory at 20 \({}^{\circ}\)C. The peak area of each compound on the 5 tubes was averaged and the relative response factor (RRF) against the internal standard, C6, was determined according to Equation (1). \[RRF=\frac{\frac{A_{i}}{m_{i}}}{\frac{A_{C6}}{m_{C6}}} \tag{1}\]  
In which:  
\(RRF=\) Relative Response Factor  
\(A_{i}=\) Average peak area compound \(i\)  
\(m_{i}=\) Mass compound \(i\)  
\(A_{C6}=\) Average peak area of the internal standard C6  
\(m_{C6}=\) Mass internal standard C6  
The results from the short-term stability studies for sulphur compounds are presented in Figures 8-10 for the 100 nmol/mol gas mixture and in Figures 11-13 for the 20 nmol/mol gas mixture.