Sampling VOCs using DTD

Direct Thermal Desorption (DTD) was used by the Materials Working Group (MWG) Testing and Standards sub group for Round Robin Testing #2 in 2019 & 2020. The analytical method was originally developed at The Indianapolis Museum of Art at Newfields.

DTD should be performed in duplicate for all agreed‐upon Round‐Robin samples using the following DTD sampling conditions:

Materials, Supplies, and Equipment

• Sample size for each trial should be noted and should fall between 3 and 20mg.
• Employ a DB‐5 chromatographic column (or equivalent) with a He carrier gas and a flow rate of 1.5 mL min^‐1.
• Using a split ratio of 20:1 is common
• Detection of ions: use a mass range of 29 to 450 m/z
• Identify volatile components using NIST 14/Wiley Registry MS databases
  • Indicate if peak identification was performed manually using a NIST library or using an automated integrated software approach.
• Minor modifications to the analysis should be reported (eg.: change in split ratio, use of a glass wool plug, etc.)
• Once peaks are identified, some assessment of the material suitability should be made using the approved list of common pollutants. Refer to the list of Compounds reported to damage cultural heritage objects, found below

Procedures

2023 protocol

Use one or more of the following DTD sampling conditions:

• Trial 1: DTD at 60°C for 10 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)

The oven temperature program is:

• 40°C for 5 min
• Heat at 10°C min^‐1 to 250°C
• Isothermal hold for 6.5 min at 250°C

Archived protocols

• 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)

Oven temperature program, regardless of trial conditions, 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.

Compounds reported to damage cultural heritage objects

(Cited from David Thickett's presentation at the Materials Working group, November 2019 [thank you, David])

Classes of compound

• Chlorides
• Mercaptans
• Carboxylic acids
• Carbonyl esters
• Peroxides
• Fumigants
• Flame retardants

Known chemical pollutants

• Acetic acid
• Formic acid
• acrylic acid
• Hydrogen sulfide
• Formaldehyde
• Acetaldehyde
• Nitric acid
• Carbonyl sulfide
• Dimethyl sulfide
• Carbon disulfide
• Styrene
• Methyl acetate
• Methyl propanate
• Ammonia
• Ethyl formate
• Vanillin
• Iso butyl benzol
• Hexanal
• 1,4 diethylbenzene
• Furfural
• Toluene
• 2 pentalfuran
• Diethylamine ethanol
• Octadecylamine
• Peroxyacetyl nitrate
• Morpholine
• 2,2,4‐trimethyl‐1,2‐dihydroquinoline
• 1,2,2,6,6‐pentamethyl‐4‐piperidinol
• 2,2,6,6‐tetramethyl‐4‐piperidinol

Round Robin Materials tested in 2020

Materials tested in the 2019 and 2020 Round Robin

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