Sampling VOCs using DTD
This method was used by the Materials Working Group (MWG) Testing and Standards sub group for Round Robin Testing #2 in 2019 & 2020 and developed at The Indianapolis Museum of Art at Newfields
Direct thermal desorption (DTD) should be performed in duplicate for all agreed‐upon Round‐Robin samples using the following DTD sampling conditions
Materials, Supplies, and Equipment[edit | edit source]
- Sample size for each trial should be noted and should fall between 3 and 20mg.
- Chromatographic separation should employ a DB‐5 chromatographic column (or equivalent) with a He carrier gas flow rate of 1.5 mL min‐1.
Procedure[edit | edit source]
- Trial 1: DTD at 90°C for 30 minutes (only for those with with cryotrapping capability)
- Trial 2: DTD at 115°C for 2 minutes (indicate cryotrap or no cryotrap)
- Trial 3: DTD at 180°C for 1 minute (indicate cryotrap or no cryotrap)
- Split ratio of 20:1 is common.
- The oven temperature program is:
- 40°C for 3 min
- 20°C/min ramp to 150°C
- 10°C/min ramp to 250°C
- isothermal hold for 6.5min.
- Detection of ions is accomplished using a mass spectrometer scanning a mass range of 29 to 120 m/z for the first 5 min to detect small volatile molecules
- Detection mass range of 45 to 450 m/z for the remainder of the analysis.
- Identification of volatile components is performed using the NIST14/Wiley Registry MS databases.
- Minor modifications to the analysis, specific to your method or process, should be noted (examples may include a change in split ratio, use of a glass wool plug, etc.)
- Participants should indicate if peak identification was performed manually using a NIST library or automated using an integrated software approach.
- Once peaks are identified, some assessment of the material suitability should be made using our approved list of common pollutants. Refer to enclosed list, Compounds reported to damage cultural heritage objects.