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February / March 2012
Technique GC/MS GC column GC, ECD detector GC, TCD detector GC, Process Figure 2: Cutting a fused silica capillary column
Because liner design and chemistry impact the transfer of compounds into the column you should always use a reliably deactivated liner that is suited to your injection technique, and change the liner as needed. These steps will maximise sample transfer and minimise sample loss at injection. For specific applications of active compound analysis, such as analysis of drugs of abuse, glass-wool liners with superior inertness are required to achieve the most reliable results. Ultra-inert liners with wool are better choices due to the efficient and robust deactivation of the liner body and the glass wool.
3. Use a column with low activity Active sites within columns that are not optimally deactivated can negatively affect peak shape and peak response. Highly inert columns minimise compound loss and degradation, and provide more accurate quantitation of active analytes, especially at trace levels. To ensure consistent column inertness, choose a column that has been tested with a rigorous test probe mixture that provides in-depth evaluation of column deactivation. When installing the column, start with high-quality ferrules and use magnification to examine column ends for chips and burrs. Figure 2 shows some examples of good and bad cuts to capillary columns. Make sure the column is positioned at the recommended depth into the inlet and detector. Figure 3 shows how active sites in a column cause peak tailing and poor response.
4. Remember your detector
If you have used inert liners and column, but still have issues with breakdown products, then active sites in your detector could be responsible. To ensure accurate quantification and high sensitivity, the entire flow path must be highly inert, including detector surfaces. This is especially true of mass spectrometers, where an inert ion
GC, FID detector GC, PID detector GC, PFPD or FDP detector GC, TSD or NPD detector Total organic carbon Zero-air generator
Filter type GC/MS Moisture and oxygen Moisture and oxygen Moisture and oxygen Process moisture Two charcoal filters (for air and nitrogen) Oxygen and charcoal Charcoal, carbon dioxide, and moisture Charcoal, carbon dioxide, and moisture Carbon dioxide and moisture Carbon dioxide and moisture Table 1. Choose the filter that meets your needs
Benefit
Higher data accuracy and less maintenance
Longer lifetime Greater sensitivity
Greater sensitivity and less maintenance
Greater sensitivity Greater sensitivity Greater sensitivity Greater sensitivity Greater sensitivity Greater sensitivity Greater sensitivity
Figure 3. Degraded peak quality resulting from active sites within a column.
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