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Evolved Gas Analysis

Couplings / Evolved Gas Analysis (EGA)

With the coupling of a Thermal Analyzer (TGA – Thermobalance, STA (TG-DSC) – Simultanious Thermal Analysis, DIL – Dilatometer) and an evolved gas analyzer like a FTIR (Fourier-transform infrared spectroscopy) or a QMS, (Quadrupole-Mass-Spectrometer) a very powerful coupling is generated which gives simultaneous (correlated) information from both instruments.

The optional Pulse-Analysis injects an exactly predetermined amount of gas into the Thermobalance (TGA) or Simultaneous Thermal Analyzer (STA). This enhances the measurement possibilities significantly.

EGA FTIR

Linseis Gasanalyse Kopplung Pfeiffer

The combination of a Linseis Thermal Analyzer with a FTIR is especially interesting in fields such as polymers, chemical and pharmaceutical industry. Linseis has more than 20 years experience in providing a integrated hard- and software concept. For interpretation different libraries are available.

Details

EGA QMS

Linseis Gasanalyse Kopplung Pfeiffer

The QMS – quadrupole mass spectrometer coupling device is a state of the art mass spectrometer with a heated inlet system. The QMS is used for the analysis of volatile decompositions. All Linseis instruments are especially designed to guarantee a user friendly operation of both the Thermal Analyzer and the Mass Spectrometer. A integrated Software solution is certainly available.

Details

EGA GCMS

Linseis Gasanalyse Kopplung Pfeiffer

By coupling a Termobalance (TGA) or a Simultaneous Thermal Analyzer (STA) with a (GC-MS) Gas chromatography–mass spectrometry which is an analytical method that combines the features of gas-chromatography and mass spectrometry, one can combine the strength on these two tools. Applications of GC-MS include drug detection, environmental analysis, explosives, and identification of unknown samples.

Details

EGA Optische In-Situ

Linseis Gasanalyse Kopplung Pfeiffer

An optical In-Situ Analysis offers many advantages such as: no Cooling / Modification of the measuring gas (for example no out-condensation, no transition reaction and no equilibrium shift).
Many materials with high condensation temperature for example alkali metals (Na, K and their combinations) are now able to be measured, heated capillary only suitable for some 200 – 250°C, the optical port allows measurement until 1600°C

Details

Typical couplings for simultaneous measurements are:

  • TG-DSC-MS (Thermogravimetry, Differential Scanning Calorimetry, Mass Spectrometer)
  • TGA-MS (Thermal Balance coupled with Mass Spectrometer)
  • TG-DSC-GC/MS (Thermogravimety, Differential Scanning Calorimetry, Gas Chromatography / Mass Spectrometry)

Analytical techniques used for coupling with thermal analyzers Couplings can be done with different gas analyzing methods:

  • FT-IR spectroscopy
  • Quadrupol mass spectrometry (QMS)
  • ELIF spectroscopy (Excimer Laser Induced Fragmentation Fluorescence)
  • Gas chromatography

The coupling of the thermal analyser with the spectrometer/chromatograph can be done by different means:

  • Heated transfer capillary (FTIR, GCMS, GC, MS)
  • Sniffer coupling (GCMS, GC, MS)
  • Optical in-situ observation (ELIF)

Heated transfer capillary

The simplest way to do a coupling is by heated capillary. In this case, a heated capillary feeds the evolved gazes from the thermobalance to the spectrometer or chromatograph. The internal diameter of a capillary is < 0,1 mm in case of a MS coupling. The capillary is heated to 200-300°C which results in the risk of condensation of outgassing during transfer and clogging of the capillary.

Sniffer coupling

his technique is used for mass spectrometer coupling. Gases pass through a very small orifice close to the sample inside the furnace and are transferred in the vacuum line to the mass spectrometer. In this way, gases are sampled at high concentration very close to the sample at high temperature and pass directly to ultra-high vacuum. This technique avoids any risk of condensationduring transfer between the thermobalance and the mass spectrometer.

Optical in-situ observation

In this case, optical windows are integrated in the thermobalance’s During heating samples often undergo phase transitions and/or weight change due to evaporation of solvents and/or chemical reactions. These changes can be detected by thermal analysis: calorimetric techniques (DTA and DSC) give information about the heat involved in these processes and thermogravimetry (TG) shows the weight change.

Weight change can be either weight increase due to oxidation reactions or weight loss due to decomposition by liberation of volatile compounds. Analysis of these evolved gases can give valuable information about the sample composition and reaction pathways for decomposition. As thermal analysis gives no information about the nature of the evolved gases, coupling with spectrometers or chromatographs is a valuable tool for evolved gas analysis (EGA).

Infrared spectroscopy

Infrared light can excite molecular vibrations in molecules. In order to be active in respect to IR-spectroscopy, the molecule has to change its dipolar momentum during excitation. Gases like CO2, CO, hydrocarbons, water vapour etc. have IR-active vibration modes while N2, O2 etc. cannot be detected.

The obtained IR-spectra allow identification of the components by characteristic vibrations which are either typical for a certain functional group (CO, COOR etc.) or for a particular compound (so called “fingerprint- region” of the spectra from 1500 – 500cm-1). Spectra libraries are helpful during spectra interpretation. Coupling to TGA and STA is a valuable tool especially in analysis of organic compounds (polymers etc.).

Mass spectroscopy

Mass spectroscopy sorts molecules by their molecular weight divided by their electrical charge (m/e). In quadrupol mass spectroscopy (QMS) molecules enter a magnetic quadrupolfield after having been accelerated in a static electric field. Molecules and their fragments are sorted by their masses and can be identified. Mass spectroscopy is very useful in order to find the molecular weight of the outgassing as well as to analyse gases which are not active in IR-spectroscopy (N2,O2, CO etc.).

Using mass spectroscopy, nearly all molecules can be detected. Also the resulting fragments of bigger molecules are often characteristic for several compounds or functional groups. This method is a common used analytical method that can be found in polymer or organic analysis as well as in forensic, medicinal, biological or inorganic areas like material science. Mass spectrometry can be also combined with a GC method that is used to get information about the purity of the substances that are investigated by the mass spectrometer. So the resulting method called GC-MS gives both, purity and molecular weight of the substrate.

ELIF spectroscopy

ELIF (Excimer Laser Induced Fragmentation Fluorescence) is a technique used for analysis of alkali metal compounds. Its measuring principle is based on a simultaneous cleavage of molecules, and excitation of the respective alkali atom by a VUV-laser. After the return of the agitated atom to its original state, a photon of a characteristic wavelength is emitted. The intensity of this “fluorescent signal” is a measure of the concentration of the compound in question. This technique is a valuable tool for characterization of alkali metal compounds (NaCl, KCl, NaOH, etc.). ELIF spectroscopy can be used only by optical in-situ coupling (see below).

Gas chromatography

The evolved gases can be a complex mixture of compounds. Column Chromatography separates these compounds before analysing them by different techniques. The chromatographic separation column has to be chosen according to the type of molecules to be separated (polar or unpolar). The most frequently used detection techniques are flame ionization detectors (FID) and thermal conductivity detectors (TCD).

 

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