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
007-5MS 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
007-5MS 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
007-5MS Silphenylene Baseline Bleed
A typical 007-5MS
baseline bleed is shown above in Figure 2.
The
mass spectrum of the baseline bleed is shown
below in Figure 3.
Figure 3
007-5MS 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
007-5MS 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
007-5MS Silphenylene Polysiloxane columns are available
in all standard column I.D.'s and in limited
column lengths.
The film thickness ranges are noted in the
chart below.