As the application scope of gas chromatography continues to expand, there have been attempts to use high-temperature gas chromatography for the analysis of non-volatile compounds. For example, the petroleum industry requires the analysis of high-boiling point hydrocarbons (C>100). Liquid chromatography may not provide satisfactory sensitivity and cost-effectiveness for this analysis, prompting the use of gas chromatography and driving the development of high-temperature gas chromatography.
High-temperature gas chromatography generally refers to the analysis where the column temperature exceeds 300°C. While the column oven temperature in conventional gas chromatographs can reach 400°C, the columns themselves have limitations. The commonly used polyimide coating on the outside of conventional fused silica capillary columns has a temperature resistance typically not exceeding 360°C. The maximum operating temperature of commonly used cross-linked stationary phases (e.g., polysiloxanes) is also around 350°C, with constant temperature usage typically below 330°C. Therefore, the key challenge in achieving high-temperature chromatography lies in addressing the temperature resistance of the stationary phase and column materials.
The development of temperature-resistant stationary phases has been a topic of interest for chromatographers. Various temperature-resistant stationary phases have been introduced throughout history, but only a few have proven to be truly applicable. High-temperature stationary phases must not only withstand elevated temperatures but also possess certain performance characteristics exhibited by conventional stationary phases, such as coating properties and separation capabilities on the capillary surface. Over time, attention has increasingly focused on developing temperature-resistant stationary phases based on polysiloxanes. In conventional gas chromatography, polydimethylsiloxane (PDMS) is known as the most thermally stable stationary phase, and its polarity can be adjusted through modifications of the substituents. Research has shown that PDMS degrades at high temperatures mainly through intramolecular cracking (random scission) and a process known as “backbiting,” resulting in the formation of cyclic oligomers, with hexamethylcyclotrisiloxane being the most abundant product. It can be inferred that the thermal stability can be improved by preventing the occurrence of these degradation reactions. To achieve this, researchers have introduced phenyl groups into the main chain of polysiloxanes to increase the rigidity of the polymer chain, allowing the highest operating temperature of the stationary phase to reach 380°C. Others have used bulky side groups to substitute methyl groups to inhibit the “backbiting” of the polymer chain. Welch Materials’ high-temperature gas chromatography columns employ a unique bonding technology to prevent the loss of the stationary phase at high temperatures, enabling a temperature range from -60°C to 400°C.
Regarding temperature-resistant column tubing, Welch Materials’ high-temperature gas chromatography columns utilize modified temperature-resistant polyimide coatings to coat specialized fused silica columns, enabling operation at temperatures as high as 400°C and extending the lifespan of the chromatographic columns.
Welch Materials High-Temperature Chromatography Column (WM-5HT) for the determination of mineral oil in food contact materials paper and paperboard food simulants according to the “SNT4895-2017 Determination of Mineral Oil in Food Contact Materials Paper and Paperboard Food Simulants.
Column and Chromatographic Conditions
Column: WM-5HT (30m0.25mm0.1μm), 07977-22007.
Stationary Phase: 5% Phenyl, 95% Dimethyl Polysiloxane.
Temperature Range: 380/400℃.
Column Oven: Start at 50℃ for 0 minutes, then increase at a rate of 2.5℃/min to 60℃ and maintain for 0 minutes. Then, increase at a rate of 22℃/min to 280℃ and maintain for 0 minutes. Finally, increase at a rate of 30℃/min to 325℃ and maintain for 12 minutes.
Injector Temperature: 275℃.
Detector Temperature: 340℃.
Carrier Gas and Flow Rate: Nitrogen, 1.5mL/min.
Split Ratio: 1:1.
Injection Volume: 1μL.
Chromatogram
Mixture of n-alkanes solution
Solution of sixteen polycyclic aromatic hydrocarbons (PAHs) standard mixture
Conclusion
Using the Welch WM-5HT (30m×0.25mm, 0.1μm) (catalog number: 07977-22007) chromatographic column under the specified chromatographic conditions meets the detection requirements.
In addition to the high-temperature gas chromatography column, Welch Materials has also introduced a new gas chromatography column with a 225 stationary phase. The WELCH 225 stationary phase chromatography column effectively addresses the production challenges of traditional 225 stationary phases, which are unstable and result in poor coating performance on the capillary surface.
Next, let’s take a look at the application of WELCH WM-225 column for the determination of Octadecanol according to the “Chinese Pharmacopoeia.
Column and Chromatographic Conditions
Column: WM-225 (30m0.25mm0.25 μm), 07919-22001.
Stationary Phase: 50% Cyanopropylphenyl, 50% Dimethyl Polysiloxane.
Temperature Range: 220/240℃.
Column Oven: Start at 60℃ for 0 minutes, then increase at a rate of 20℃/min to 180℃ and maintain for 0 minutes. Then, increase at a rate of 10℃/min to 220℃ and maintain for 10 minutes.
Injector Temperature: 270℃.
Detector Temperature: 280℃.
Carrier Gas and Flow Rate: Nitrogen, 1.0mL/min.
Split Ratio: 10:1.
Injection Volume: 1μL.
Chromatogram
Mixed standard solution
Analysis Result Table
Column System Evaluation Table
Test sample
Analysis Result Table
Column System Evaluation Table
Conclusion
The use of WELCH WM-225 (30m × 0.25mm, 0.25μm) (Product Code: 07919-22001) column meets the detection requirements under the specified chromatographic conditions.
The above is a brief introduction to two chromatographic columns newly introduced by Welch Materials.
In addition, Welch Materials has been focusing on the research and production of gas chromatography columns for many years, with advantages such as high inertness, low bleed, high column efficiency, and long lifespan. The company has launched 22 types of capillary gas chromatography columns for popular applications such as organic chlorine analysis, liquor component analysis, and TVOC analysis. With excellent product performance and a comprehensive after-sales service system, Welch Materials’ gas chromatography columns have been widely used in universities, research institutes, pharmaceuticals, petrochemicals, brewing, environmental protection, and other industries.
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