Chromatography: time to get connected

Lindy Miller, Agilent Technologies takes a look at achieving an inert gas chromatography flow path through better GC connections

Gas chromatography (GC) and GC/MS are powerful techniques for trace level analysis across a range of applications. Regulatory agencies are increasingly pushing for lower levels of detection of active compounds. At the same time, sample matrices are becoming more complex. Balancing these trends is a challenge for analysts who need to maximize sample throughput, while keeping systems within calibration. To avoid re-runs and improve productivity, analysts seek tools that help systems hold calibration, even after injection of samples with difficult matrices. An inert GC flowpath has been shown to extend the time and number of samples between calibration.

Flow path inertness is at the cutting edge of GC and by optimising the transfer of analytes from the injector through the GC flowpath the signal can be increased. This allows the analyst to extend the calibration range. This optimization can now be achieved by considering all the components of the GC flowpath, in particular ensuring robust and leak-free GC connections.

Improving GC sensitivity through an inert flow path

In gas chromatography, inert surfaces in the flow path from the inlet through the column to the detector are essential for achieving good peak shapes, low levels of detection and accurate results for active analytes. Active sites along a non-inert GC flow path (such as injector, column, liner and detector) can latch onto active analytes and degrade peak shapes, or can absorb trace analytes completely.

A lack of inertness can negatively impact GC sensitivity but by following these five steps you can achieve an inert GC flow path for optimum GC sensitivity: 

• Maintain the inlet to help ensure peak instrument performance and productivity
• Prevent sample loss at injection by using a deactivated liner suited to your injection technique
• Select a column with optimized inertness to minimize compound loss and degradation for more accurate quantitation of active analytes, especially at trace levels
• Remember your detector  for mass spec systems, use an inert source to ensure accurate quantification and high sensitivity
• Use a gas purifier to provide a clean, high quality gas supply that is free of oxygen and contaminants

Column selection in particular is a key consideration for an inert GC flowpath as column bleed can cause baseline noise and interference. Poor GC column performance can also affect productivity and data quality. The use of high-performance GC columns delivers better results when it comes to inertness and column bleed.

Better GC connections

Ever since the technique’s invention, leaking GC column connections have been a source of frustration and wasted time in GC laboratories. Time is often spent troubleshooting and manually re-tightening column, retention gap and transfer line connections using a wrench – time which could otherwise be spent analysing results or running more investigations. Due to this time impact, as well as the critical impact on results and instrumentation, preventing GC leaks becomes a priority for those looking to achieve an inert flowpath.  

GC column connections leak because capillary column ferrules made of graphite-polyimide blends loosen after repeated heating cycles, creating gaps in the mechanical fitting. This can lead to instability of detector baseline, noise and questionable results. On top of this, leaks at the GC column fitting can also cause significant losses of expensive high quality gas, shorten equipment lifetimes, and destroy columns. Furthermore, some detectors can be damaged by exposure due to high column bleed caused when oxygen diffuses into the flowpath from leaking column connections resulting in inaccurate results and costly instrument downtime.

New GC supplies have been developed to help ensure column connections are secure by offering a tight, consistent seal without the need for expensive system upgrades or adaptors. One such development is the Self Tightening column nut from Agilent.

Maintain, prevent, protect

Increasingly stringent demands on GC systems for sensitivity, accuracy and reproducibility means that analysts need access to the tools to create an inert GC flowpath. By investing in the right chromatography supplies, researchers carrying out trace-level analysis can discover how the right GC connections really do make all the difference.