It’s a common problem for laboratories running gas chromatography analyses: After several injections of certain “dirty” extracts like food products into the GC columns, matrix residue builds up in the inlet liner, changing (lowering or increasing) the response of certain sample compounds, affecting the accuracy of the analysis.
Performance can be restored by exchanging the GC inlet liner. Traditionally, this exchange has had to be done manually by the analyst, stopping the analysis sequence.
Automated liner exchange (ALEX) solves the problem without direct human intervention, restoring the original performance of the GC system and boosting throughput. It’s a popular solution for labs involved in the analysis of extracts that contain nonvolatile matrix residue.
Automatic liner exchange (ALEX): a built-in feature of MPS Robotic
ALEX is a built-in feature of the new GERSTEL MPS RoboticPRO, a highly efficient GC/MS and LC/MS autosampler that represents the latest in PAL3 autosampler technology. ALEX is one of several design features that allow the MPS RoboticPRO to perform routine tasks reliably and accurately with unmatched throughput.
Since changing the liner after injecting dirty samples is important for ensuring your sample analysis is free of matrix interference, our scientists conducted a study to show the advantage of the ALEX feature for the determination of pesticides in spinach samples.
Study: spinach-pesticide extract analysis
In our study, a spinach extract was spiked with 60 pesticides to demonstrate the effects of nonvolatile matrix residues deposited in the GC inlet liner. Raw, uncleaned extract was injected repeatedly and analyte discrimination effects were obvious after just a few injections. Automated liner exchange using the GERSTEL ALEX technology restored the analysis system to its original performance, enabling routine GC-based analysis of large numbers of extracts prepared using the QuEChERS (quick, easy, cheap, effective, rugged and safe) approach.
A frozen sample of organically grown spinach was homogenized and extracted with acetonitrile as described in the QuEChERS procedure. The cleanup step was left out and the raw extract was spiked with the pesticide mixture. The resulting solution was used for repeat injections into the ALEX system. A series of 5 μL samples of spiked raw spinach extract were injected into the ALEX/CIS inlet and analyzed. The first series spanned 20 injections with a liner exchange after 10 injections. The second series spanned 20 injections with liner exchange every five injections.
Restoring analytic performance
The first series of 20 injections with liner exchange after 10 injections showed four compounds that were strongly affected by matrix effects. Calculations based on the internal standard tetraconazole did not change the profile; 12 of the 60 compounds were affected by matrix buildup.
Exchanging the liner after every five injections improved the stability of peak areas and the relative standard deviations for compounds susceptible to matrix effects. Our study proved that the ALEX system is a powerful tool for automated handling of samples with a high matrix load without compromising the accuracy of the results.
Feel free to reach out for a deeper conversation about ALEX or how the MPS RoboticPRO can improve throughput in your lab.