Hyphenation refers to the process of connecting two or more instruments together for the purpose of increasing the amount of information obtainable from a sample.
Hyphenation refers to the process of connecting two or more instruments together for the purpose of increasing the amount of information obtainable from a sample. Hyphenating thermogravimetric analyzers (TGA) with mass spectrometers (MS) and Fourier Transform Infrared (FTIR) spectrometers has a long history. The ability to combine spectroscopic data for the purpose of chemical analysis, with the mass loss data from the TGA has born fruit over numerous material science fields. For example, the pharmaceutical industry routinely monitors for the presence of solvent in their products. Evolved gas analysis can provide information on degradation pathways, reaction products, and/or chemical composition.
In addition to MS and FTIR, the desire to hyphenate a TGA to GC-MS instruments is also of great interest to users. But whereas MS and FTIR are continuous techniques (i.e. they continuously collect spectra during the execution of the TGA experiment), GC-MS is typically not continuous. On the other hand, GC-MS will give the most complete chemical information about the evolved gas.
Further information on all three techniques can be found in the TA Instruments webinar linked below. You can also click on the individual links for each technique to learn more about TA Instruments various solutions for hyphenation.
Thermogravimetric Analyzers/Fourier Transform Infrared Spectroscopy (TGA/FTIR)
Fourier Transform Infrared Spectroscopy, or FTIR, refers to a spectroscopic technique where a sample is irradiated with infrared radiation of a specific wavelength range. Depending upon the chemical nature of the sample being irradiated, some wavelengths will be absorbed, and some will not, thereby producing an absorption spectrum. These spectra are typically searchable in a library for the purpose of identification. The webinar linked to below gives an overview of the technique.
Most benchtop instruments for TGA hyphenation are mid-IR instruments, meaning they operate over a wavenumber range of 40 to 4000 cm-1. In order for a molecule to absorb IR radiation, it must have an electric dipole moment. Therefore symmetric molecules, such as nitrogen or oxygen, will not be IR active.
- Thermal Analysis Application Brief: High Resolution TGA / Mass Spectroscopy Characteristics of Fuel Oil Transport Additives
- Weight Loss Determined from Mass Spectrometry Trend Data in a
Thermogravimetric/Mass Spectrometer System
- TGA Webinar – Evolve Gas Analysis with Mass Spectrometry
- Using A Modified Method of Standard Additions for Quantification of TeflonTM
in Grease by TGA/MS
- Discovery TGA Brochure
- Discovery SDT Brochure
Thermogravimetric Analyzers/Mass Spectroscopy (TGA/MS)
Mass spectroscopy is a spectroscopic technique whereby an input gas is ionized, usually by collisions with electrons in the 40 to 70 eV energy range. The ionized species are passed through a mass filter, which eliminates all but a single mass-to-charge species. This species then impacts a detector. The mass filter is scanned continuously over the unit’s mass-to-charge range, typically 1-300 atomic mass units (amu) for most benchtop instruments, thereby producing multiple spectra as the TGA scans in temperature.
The technique is very sensitive – capable of detection limits in the ppb range, depending upon the gas being analyzed. The webinar linked to below gives an overview of the technique.
Thermogravimetric Analyzers/Gas Chromatography-Mass Spectrometers (TGA/GC-MS)
GC-MS refers to an instrumental technique whereby the chemical components of a gas are separated by passage through a chemically activated column. The interior of the column is coated with a stationary phase and the gas components that pass through it show varying affinities for this stationary phase. After passing through the column and being chemically separated, the gases are input into a mass spectrometer for identification.
The technique will give the most chemical information of the techniques discussed. However, because of the time required for the gas to pass through the column, it is a non-continuous method. This is as opposed to MS and FTIR which are continuous methods.
Multiple Hyphenation (TGA/GC-MS/FTIR)
Multiple hyphenation typically refers to TGA/FTIR/MS and TGA/FTIR/GC-MS setups. Hyphenating more than one spectroscopic technique to a TGA allows for the maximum data from a single sample. Also great flexibility attends multiple hyphenation units. One can vary the number and type of spectroscopic instruments utilized depending upon the experimental needs.
Concerning TGA/FTIR/MS multiple hyphenation, since MS units typically do not require much gas (units draw about 1 sccm of gas through the capillary), the rest of the effluents exiting the TGA can be easily sent to an FTIR. Concerning TGA/FTIR/GC-MS, dedicated hardware is required to ensure efficient flow of gas through the FTIR gas cell and into the GC-MS. Such hardware is also required for standalone TGA/GC-MS interfacing.