Troubleshooting in Gas Chromatography - Forensic Applications of Gas Chromatography - page 65

Time (mins)

Time (mins)

Figure 6.6 Example of a loss of separation.

6.5 Loss of Separation or Resolution

A loss of separation or resolution (Figure 6.6) will cause issues on the data
acquisition software output as the PC operated system is relying on com-
pounds appearing at almost the same time in order to identify them (by reten-
tion time). A loss of separation (or resolution) can occur due to a number
of possible options, including an ageing column that has lost a substantially
amount of stationary phase (remedy: replace the column with the same sta-
tionary phase and dimensions), the carrier gas flow rate has changed (remedy:
check that gas supply pressure has not changed) and the temperature pro-
gramme has changed (remedy: check that the method has not been altered).

6.6 Loss of Sensitivity

A loss of sensitivity (Figure 6.7) is ultimately going to affect the ability of
the instrument to perform its key functions (i.e., identifying and quantify-
ing compounds). A loss of sensitivity can occur due to a number of possible
options, including that sample concentration has changed (remedy: recheck
calculations and dilutions to ensure no mistakes have been made in the prep-
aration of the sample), carrier gas flow rate has dramatically changed (rem-
edy: check that gas supply pressure has not changed), the injection port liner
is dirty (remedy: replace the liner with a new, deactivated liner), temperature
programme has dramatically changed (remedy: check that the method has