GRS-5MS GC Capillary Column

Traditional polysiloxane-type GC stationary phases degrade at elevated temperatures. The degradation process is well documented and consists of the thermal rearrangement of the siloxane backbone to produce cyclic groups. These groups are volatile and elute from the column as column ‘bleed’. The silphenylene units (Fig. 1) within the GRS-5MS backbone act as heat sinks and limit the formation of the cyclic groups normally associated with polysiloxane degradation.

Figure 1, Silphenylene/polysiloxane phase unit.

The GRS-5MS silphenylene columns offer the chromatographer a number of advantages:

• greater thermal stability
• greater resistance to oxygen degradation
• fast ramping to elevated temperatures to purge the column of residual components
• improved analysis of trace level compounds
• less baseline bleed equals less baseline noise, which results in lower detection limits
• increased column lifetimes
• reduced contamination of MS sources and other GC detector surfaces
• “cleaner” mass spectra…mass spectra with fewer extraneous ions enables the analyst to achieve more accurate compound identification and a more efficient library search

Figure 2, GRS-5MS Silphenylene Baseline Bleed

A typical GRS-5MS baseline bleed is shown above in Figure 2. The mass spectrum of the baseline bleed is shown below in Figure 3.

Figure 3, GRS-5MS Silphenylene Mass Spectrum.
Note the low abundance of key ions.

While a typical methylpolysiloxane bleed spectrum shown below in Figure 4. yields high abundance’s of ions with m/z 207, 281, 355, the mass spectrum of the GRS-5MS silphenylene column (above, Fig. 3.) yields significantly lower abundance of these ions. Additionally, it is apparent from Figure 3 that there is a reduction in the total number of ions resulting in “cleaner” spectrum and less background interference.

Figure 4, Typical Methylpolysiloxane Mass Spectrum