Success all around: The repeatability experiments gave good results and even after ten CIS Pyrolysis runs the liner needed neither replacing nor cleaning. “No trace of carry over between samples” said Dirk Bremer, GERSTEL R&D Manager, shown to the right in the picture along with Patric Eckerle from DOW.
Improved peak shape: The GERSTEL CryoTrap System (CTS) significantly improved both separation capacity and accuracy in the determination of volatile pyrolysis fragments by focusing these and sharpening the peaks.
First class results: Repeatability of 10 CIS pyrolysis runs of an S/B copolymer. The CIS was not cleaned or replaced over the course of these runs.
Successful quantitation: Peak pattern obtained following pyrolysis of a synthetic standard. Standards with various concentrations of butylacrylate and styrene in a styrene/butadiene copolymer were pyrolyzed in the project. Results were obtained faster than when using spectroscopic methods. The key fragments butanol and butylacrylate were simultaneously identified by GC/MS.
Polymer analysis and the instrument set-up used: Agilent Technologies 6890 GC with GERSTEL CIS 6 inlet and FID as well as a MultiPurpose Sampler used for automated sample preparation and sample introduction. A GERSTEL CryoTrap System (CTS) was used to focus and improve the determination of volatile pyrolysis breakdown fragments.
Pyrolysis of polyethylene using the GERSTEL CIS 6 inlet. Overlay of two successive pyrolysis GC runs. The sample was dissolved in hot toluene. Agitator temperature: 125 °C; Syringe temperature: 125 °C.
Pyrolysis GCxGC enables high performance polymer analysis: 2D chromatogram of polyethylene fragments shown in a 3D presentation. The identification of micro-structures, information on monomers used, as well as the identification of additives, is significantly improved compared with standard GC chromatograms.
Efficient Automated Pyrolysis GC
Scientists from Dow, a leading producer and supplier of chemicals and polymer products, have collaborated with GERSTEL scientists in developing a novel method for determining the structure and composition of polymers. The approach: Following a high-temperature liquid sample introduction, pyrolysis is performed in the high-temperature version Cooled Injection System 6 (CIS 6) GC inlet. Pyrolysis break-down products are subsequently determined using GC/FID or GC/MS.
Monomers are generally low molecular weight compounds with special functional groups that enable polymerization. Depending on the structure and properties of monomers, and on the conditions chosen, polymerization can lead to the formation of linear, branched, or cross-linked polymers, which have different chemical and physical properties. In order to determine the structure of a polymer, pyrolysis GC is often used as the technique of choice;
it is a powerful tool in the characterization of complex polymers whether they are in solid or liquid form or in emulsion.
Curie-Point pyrolyzers are widely used for polymer analysis. Some are based on resistive heating, some on microwave technology. Technical aspects aside, the use of special pyrolyzers can be labor intensive, sometimes requiring additional cumbersome sample preparation steps as well as significant added investment volume. A different, simpler, and more cost-effective way has been described by scientists from DOW and GERSTEL who cooperated on developing an attractive alternative to standard methods.
“Instead of a dedicated pyrolyzer, we used the CIS 6, the high-temperature version of the GERSTEL Cooled Injection System (CIS)”, says Patric Eckerle, Dow Germany. The GERSTEL CIS is the most widely used PTV-type inlet in the world. Liquid polymers and polymer mixtures were pyrolyzed directly in the GC inlet in an oxygen-free carrier gas atmosphere. Pyrolysis break-down products were then transferred to the GC column, separated and determined using a Flame Ionization Detector (FID).
To prove the validity of the method, the scientists analyzed different polymer mixtures:
- An emulsion based on a 1:100 styrene-butadiene polymer mixture diluted with water was examined in order to determine recovery rates. In this context, Eckerle examined the influence of the GERSTEL CryoTrap System (CTS) on the quality of the separation.
- A styrene-butadiene polymer mixture containing varying amounts of emulgated copolymer (butylacrylate-styrene) was analyzed in order to verify the quantitation.
- Polyethylene (PE), dissolved in hot xylene, was analyzed using two-dimensional GC (2D GC and GCxGC).
For the polymer analysis, the experts used a GC system with a GERSTEL MultiPurpose Sampler (MPS), which was used for automated sample preparation and sample introduction. The MPS was equipped with a headspace syringe adapter, a heated 10 µL syringe and a heated agitator. The GC 6890 from Agilent Technologies was fitted with a GERSTEL CIS 6 programmed temperature vaporizer as well as an FID.
And this is how Eckerle and his colleagues approached the task: Following sample preparation, 0.5 to 2 µL of the dissolved polymer was introduced into the cool CIS liner. Solvents were then purged from the inlet through the split vent, leaving the polymer material condensed on the CIS liner walls. The temperature of the CIS was kept at 90 °C for 3.5 minutes during the solvent purge step. It was then programmed at 10 °C/min to 600 °C, a temperature sufficiently high for complete pyrolysis of the sample. The temperature was lowered after a one minute hold time.
The separation was performed using GC with and without column switching based on the following columns: HP 5 ms, 30 m x 0.25 mm I.D. x 0.25 µm film thickness from Agilent Technologies; in the 2D GC (GC x GC) setup, the following column was also used: Zebron ZB 50 ms, 30 m x 0.25 mm ID x 0.25 µm film thickness from Phenomenex. The oven temperature was kept at 50 °C for 6 minutes and then programmed at 15 °C/min to 325 °C (8 min). The split flow was 20 mL/min and the FID temperature was set to 330 °C (standard gas flow conditions). Quantitation was performed based on standard addition.
The purpose of the exercise
„Using the CIS 6 as a pyrolysis module was a complete success“, Patric Eckerle said. „A butylacrylate/styrene copolymer in a styrene/butadiene copolymer was determined qualitatively and quantitatively with minimal method development time. In addition, pyrolysis patterns of standards containing different amounts of butylacrylate/styrene copolymer in a styrene/butadiene copolymer were successfully reproduced. Key fragments such as butanol and butylacrylate were identified by GC/MS and when we added a GERSTEL CryoTrap System (CTS), peaks were sharpened significantly, enabling us to improve separation and to focus and accurately determine volatile pyrolysis products”.
Reproducibility and repeatability were excellent, and even after 10 pyrolysis runs, it was not necessary to clean or replace the CIS liner. “There was no sign of memory effects”, said Dirk Bremer, GERSTEL R&D Manager. “The CIS 6 - Pyrolysis - GCxGC system we used for polymer analysis gave a high peak yield and the correlation between the peak areas and control standards was outstanding”. J. Sep. Sci. 2008, 31, 3416-3422.
The conclusion drawn by Mr. Eckerle is that CIS 6 pyrolysis is well suited for several things: The determination of monomers in polymer mixtures; to gain information on micro-structures; and to identify additives in polymers. “Our CIS 6 based pyrolysis method is efficient, fast and inexpensive - and it requires much less manual sample preparation than standard methods”, says Eckerle, while adding: “It is also very promising that the method is faster than many spectroscopy-based methods we have otherwise used and the quality of the data is outstanding. You could literally place pyrograms on top of each other with a perfect match and we were able to get both qualitative and quantitative results”.