This introduction assumes the reader has skills and experiences in GC and GC/MS analysis or, having no or limited experiences in pyrolysis-GC (Py-GC), is willing to learn and use it in the future.
4. Four analytical techniques
Four analytical techniques that use Frontier Labs pyrolyzer are shown below.
- Evolved Gas Analysis (EGA-MS)
- Single-shot analysis
- Double-shot analysis
- Heart-cut EGA-GC/MS (HC/EGA-GC/MS)
Using these analytical techniques, unknown polymer materials can be analyzed in detail.
Polymer analysis is usually started by performing EGA-MS in which a sample is gradually heated to a high temperature. The information obtained here is vital for the other analytical techniques (2~4) listed above. These analytical techniques are extremely useful tools for unknown polymer analysis.
4.1 System configuration for four analytical techniques
The system configurations for the four analytical techniques are shown in Fig. 9. Vent-free GC/MS adapter used in each technique is a product that permits column exchange without venting the MS.
4.2 Analysis flow for unknown polymer
Typical analysis flow for an unknown polymer is shown here.
First, Evolved Gas Analysis (EGA)-MS is performed on an unknown polymer and the thermal characteristic data for the polymer is obtained from the EGA thermogram. The data obtained here is used in subsequent steps of analysis.
The unknown polymer can be identified using analysis data obtained and F-Search, a library and search software which permits not only identification of polymers, but also identification of additives in a polymer.
4.3 Evolved Gas Analysis-MS (EGA-MS)
Vent-free GC/MS Adapter, used in this technique, is a product that permits column exchange without venting the MS. In Evolved Gas Analysis (EGA-MS), a deactivated metal tube is used to connect between GC injector and MS detector. By programmed heating of a sample, released gases are detected by MS. The resulting chart is called an EGA thermogram.
In Fig. 12, five peaks were observed for this sample. Peaks observed in low temperature regions are volatile compounds derived mainly from residual solvents, unreacted monomer, and additives. Peaks observed at higher temperatures are the pyrolyzates of a polymer.
The number of peaks and the temperature zone for each peak are vital information in determining correct temperatures for single-shot, double-shot and heart-cut analyses.
4.4 Single-shot analysis
Single-shot is a flash pyrolysis technique in which a sample is pyrolyzed in a pyrolyzer furnace whose temperature has been set at a high temperature, and the pyrolyzates formed are immediately introduced to a GC separation column for analysis.
The pyrogram shown in the figure below was obtained by single-shot analysis at 550 ºC, which is approximately 50 ºC higher than the pyrolysis end temperature of a polymer obtained from an EGA thermogram.
The analysis procedure is very simple; however, a single pyrogram contains the information for all the temperature regions of the EGA thermogram, making the analysis difficult depending on samples. In such a case, double-shot analysis described shortly is a useful alternative.
4.5 Double-shot analysis
In this technique, a sample is analyzed in two steps.
MicroJet Cryo-Trap, used in the System configuration for double-shot analysis (Fig. 15), is a product that permits volatile compounds to be cryo-trapped temporarily at the head of a separation column by liquid nitrogen
In STEP 1 below, volatile compounds in a sample are analyzed first by thermal desorption (TD)-GC/MS. This makes the analysis of volatile components separate from that of the polymer, thus simplifying identifications.
The chromatogram below shows the volatile components in peaks A through C depicted in the EGA thermogram above. Using MicroJet Cryo-Trap, volatile components are revealed as sharp peaks.
The pyrogram below shows pyrolyzates of the polymer which shows up as peaks D and E in the EGA thermogram above. Acrylic resin and dimethyl siloxane are found to be present.
4.6 Heart-cut analysis (HC/EGA-GC/MS)
Heat-cut analysis is a GC/MS technique in which compounds released from any temperature zone in an EGA thermogram are selectively introduced into a separation column. This technique requires Selective Sampler and MicroJet Cryo-Trap and allows automatic GC/MS analysis of up to eight temperature zones.
In the figure below, chromatograms and pyrograms A through E are obtained by HC/EGA-GC/MS of peaks A through E, each having a specific temperature zone.
The Selective Sampler, used in the system configuration of HC/EGA-GC/MS (Fig. 17), is a product that permits compounds released from any temperature zone in an EGA thermogram to be introduced into a separation column for analysis.