Identification of sink spots in two thermal desorption GC/MS systems for the analysis of polycyclic aromatic hydrocarbons

- Incomplete thermal desorption (TD) recovery of PAHs was observed.
- Degree of incompleteness was linked to volatility of a compound.
- Sink spots in thermal desorption systems that retain PAHs were identified.
- Short-path TD had better recovery for PAHs than two-stage TD.

Thermal desorption (TD) GC/MS has been used for the analysis of polycyclic aromatic hydrocarbons (PAHs) and other semi-volatile organic compounds. However, thermal desorption recovery of PAHs have not been well studied and the cause of PAH residues in a TD system has not been clearly understood. Our results showed that low volatility of PAHs can lead to their incomplete recovery in a TD system: for the PAHs with low vapour pressures, up to 10% and 3% could be lost in a two-stage (TS) TD system and a short-path (SP) TD system, respectively. Within the TSTD system, the majority of residues were found in the 4-port valve and in the spot where internal trap and the 4-port valve connects. Within the SPTD system, residues were largely confined to the tube needle connecting the sample tube and GC injection port as well as inside the injection port. Since the volatility of PAHs can represent the range typical of semi-volatile organic compounds (SVOCs), our results have a wide implication for the thermal desorption of SVOCs in general.

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