shows the separation of C1-C5 hydrocarbons
using Al2
O3
, but operated at different
temperatures. The peak shapes for both
1,3-butadiene and methyl acetylene improve
at higher temperatures. It should also be
noted that changing temperature will initiate
another effect � the alumina will become
less`polar.'The result being that unsaturated
(polar) hydrocarbons will elute faster relative
to saturated (non-polar) hydrocarbons. This is
why, in the example, both peaks elute closer
to the pentane peaks.
In practice
To solve an overloading issue that impacts
on quantification a new column with more
capacity or solubility can always be applied.
Initially, it is preferable to overcome the
challenge using the existing column by
reducing the absolute amount of sample
compound injected on to the column. This
can be done via:
� Injectingless,smallersamplevolume,
higher split ratio (Figure 6).
� Dilutingofthesamplepriortoinjection.
By doing this a higher sensitivity setting of
the detector must be used. However, if this
does not solve the problem, a column with
more capacity/solubility is required.
Acknowledgements
SpecialthankstoBillBromps,RestekR&D
Figure 5
1 2 3 4 5 6 7 8
0
50
100
150
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00.0
0
25
50
75
100
125
Figure 5: Impact of temperature on peak shape of 1,3-butadiene and methyl acetylene. Column: 30 m x 0.53 mm
Rt-Alumina BOND/Na2
SO4
. Peaks: 1 = 1,3-butadiene, 2 = methyl acetylene.
Figure 4
Time (min)
(a)
(b)
Figure 4: Impact of absolute sample load on solid stationary phase/PLOT column. Column: 30 m x 0.32 mm Rt-Alumina BOND/KCl: (a) overloaded injecting 50 ng
per component, (b) injecting 5 ng/component. Peaks: 1 = pentane; 2 = methylacetyene; 3 = pentane; 4 = 1,3-butadiene.
40 chrom doctor www.sepscience.com
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