Sample Preparation – TGA-MS

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Sample Pans – pan materials depend on maximum temperature needed and sample interactions with the pan

Sample materials / Pan types	Pt / Rh	Al	Al2O3
Salts, general	No reaction	No reaction	Do not use
Metals, general	Reaction damage	Do not use	Some possible reactions
Polymers, general	No reaction	No reaction	No reaction
Carbon materials, general	Possible high temperature reactions	No reaction	Possible high temperature reactions
Inorganics, general	Possible high temperature reactions	Possible high temperature reactions	Possible high temperature reactions
Silicon	Do not use	No reaction	Do not use
Iron oxide	No reaction	No reaction	Do not use
Magnesium fluoride	No reaction	No reaction	Do not use
Graphites	Possible high temperature reactions	Possible high temperature reactions	Possible high temperature reactions
Carbonates	No reaction	No reaction	Possible high temperature reactions
Sulphates	No reaction	No reaction	Possible high temperature reactions

• Aluminum pans are one-time use only.
• Alumina (ceramic) pans are typically used if the sample is reactive or possibly reactive.
• Other pan materials, such as sapphire, are also possible, but must be provided for sample analysis.
• Use a pinhole or sealed pan for samples requiring air-sensitive or alternate atmosphere analysis.
• Reference pans should match the sample pan materials (e.g., alumina reference when using alumina sample pan and platinum reference when using platinum or HT platinum sample pans).

Platinum and alumina pans are re-usable but should be cleaned before (preferably) and after (especially) sample acquisition.

• Alumina pans are cleaned first using a dry cotton applicator to remove remaining residue and then with a solvent (acetone, isopropanol, or other applicable solvent) soaked cotton applicator. The pan is then air dried.
• Platinum pans are cleaned by fire immersion. Pans should be held in a flame for several seconds, rotating so the fire reaches all surfaces.
• Pans should be discarded when they become discolored, overly burnt, or deformed.
• For some organics, oxides, or other salt materials, platinum or alumina pans might be restored using additional cleaning or buffing methods. Please see the User Portal for more information on how to proceed.

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Sample material – liquids and various solids (powders, films, crystals, etc.) are applicable. Samples should be representative of the bulk material. Mixing or composite methods should be applied to ensure bulk similarity to the analyzed sample.

• Need at least 1 mg material. Typically, sizes range from 1 – 30 mg. For most polymer or organics analysis, 5 – 10 mg is recommended. For TGA-MS, only 0.5 – 5 mg should be used and 0.5 – 2 mg is recommended.
• Liquids should cover the pan bottom but should not be close to the pan edges as this could lead to sudden and unexpected sample loss prior to or during acquisition.
• Ensure the pan bottom is covered with sample material. Ideally, the pan bottom should be flat (not deformed or bent) so the material can be evenly distributed and the handle should be uniform so the pan hangs level.
• Grinding large crystals or films increases the overall surface area and increases reproducibility.
• Use approximately the same weight of material for each replicate to ensure reproducibility.

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Special considerations or experiments

For any of these experiments, please contact the Lab Manager directly to discuss specific experimental and sample preparation requirements as well as coordinate instrumentation time.

• Explosive materials – only small amounts of explosive materials should be used. Material should be combined with an excess of inert material, such as aluminum oxide powder. Any samples known or suspected to be explosive hazards should be explicitly stated as such on the submission form.
• Purge gas – the standard TGA purge gas is nitrogen (N₂). Additional purge gases are also available upon request: air, helium (He), argon (Ar). Purge gases may also be used in combination to determine gas reactions and/or reaction products (via TGA-MS analysis).
• Alternate atmosphere analysis – samples may be enclosed in a pan containing an alternate atmosphere, such as nitrogen, for air or water sensitive samples. Working in a glove box, samples are sealed in pans. The pans are punctured just prior to analysis, minimizing time in an air environment, prior to the sample being moved to the furnace where a nitrogen (or other approved selected gas) flushed out the remaining air prior to sample analysis.
• Mass spectrometry (TGA-MS) – gaseous decomposition and/or reaction products are sampled by a residual gas analyzer (RGA) mass spectrometer during TGA analysis. MS monitoring can be done via spectral scanning (1 – 300 amu), which is useful for initial TGA-MS investigations or if NIST EI-MS spectral matching is desired, or discrete ion traces, in which individual ion abundances can be monitored throughout the TGA-MS experiment. If NIST EI-MS library searching of TGA-MS spectra is needed, please contact Dr. Bailey to schedule computer time. Purge gas choice will affect background signal and may complicate NIST database matching. If isobaric (different gasses with the same, or nearly the same, mass) interference is anticipated, a different purge gas may be useful, especially for scanning experiments:
  • Nitrogen (N₂): background masses 14 and 28 amu. These ions, especially 28 amu, are common during electron ionization and/or as TGA decomposition products.
  • Argon (Ar): background masses 9 and 18 amu. These ions, especially 18 amu, are common during electron ionization and/or as TGA decomposition products.
  • Helium (He): background mass 2 amu. Few, if any, isobaric influences have been reported.
• Modulation – if sample amounts are limited, transitions are small, or for decomposition kinetics (improved over traditional multiple reaction methods). Some applications include:
  • polymer characterization and lifetime studies
  • model-free kinetics
  • hazard potential of materials
  • complex reaction studies (overlapping weight losses)
  • drying processes
  • direct measurement of activation energy