Comparing Liners and Their Effects on Compounds
What is a Liner?
Liners are glass tubes situated in the injection port of a gas chromatogram, which are secured by O-rings, as shown in the Figure 1. The rings purpose is to ensure a reliable seal, temperature stability and system longevity. Crafted from inert material, liners are delicate, making the column installation into the liner a critical step, which is also shown in the image below. The depth to which the column is inserted into the liner is of utmost importance, as an incorrect installation could lead to consequences such as column overloading, sample discrimination, temperature variations, potential liner damage and inconsistent results.
Despite their simple appearance, liners wield significant influence in multiple aspects of analysis. Serving as the initial point of contact for the sample, they ensure its integrity from injection to vaporization. By preventing sample degradation, adsorption and contamination, liners contribute to the accuracy, precision, and reproducibility of the analytical results. Their inert nature minimizes interactions with sample components, ensuring no contribution to unwanted peaks. Additionally, liners promote optimal and uniform sample vaporization, reducing sample matrix effects and safeguarding the column.
Figure 1. General display of the liner in the injector port of the Gas Chromatograph.
However, the efficacy of the method varies depending on its applications and requirements, with certain liners proving superior to others. Among the commonly utilized liners are Straight (with or without Quartz Wool), Taper (with or without Quartz Wool), Focus, and Taper Focus Ultra. Our comprehensive tests have showed the advantages and distinctions among these liners, with all test parameters and equipment detailed in Appendix I.
Comparing Different Liners
A notable finding is the potential enhancement in peak area when employing different liners. This not only results in increased sensitivity but also holds significant importance when the tested method falls short of meeting desired detection criteria. For instance, in our laboratory experiments, TAPER QUARTZ WOOL (TAPERQW) demonstrated a capability to augment the peak area of components compared to STRAIGHT QUARTZ WOOL (STRQW). Specifically, the average peak area of P-xylene with TAPERQW measured 1281, whereas with STRQW, it was 838 µV.Min, a significant difference as illustrated in Figure 2. Furthermore, the reliability of the conducted test is reinforced by the duplicate analysis of the standard mix, with the determination of the Relative Standard Deviation (RSD %) measuring below 10% for both, as shown in Figure 3.
Figure 2. Chromatograms of P-xylene when TAPERQW (top) and STRQW (bottom) liners are used.
Figure 3. Statistical analysis regarding peak area between TAPERQW and STRQW.
Additionally, the use of different liners can impact peak symmetry. Our investigations revealed that the FOCUS liner could enhance the peak symmetry of compounds compared to TAPERQW or STRQW. For instance, 4-methyl-2-pentanone exhibited an average asymmetry of 1.16 with the FOCUS liner, while with TAPERQW and STRQW, this average increased to 1.21 and 1.24, respectively. It is crucial to note that for an acceptable peak, asymmetry should fall between 0.90 and 1.20, with values closer to 1 being ideal. In the case of the other two liners, asymmetry slightly exceeded the limits, whereas the FOCUS liner maintained peak shape within the specified requirements. Figure 4 visually represents the peak shape of 4-methyl-2-pentanone when each of the three liners were employed. Notably, the onset of peak tailing is noticeable when TAPERQW and STRQW are used, while FOCUS demonstrates no fronting or tailing. As known, the presence of tailing or fronting can adversely affect the accuracy and precision of analytical results.
Furthermore, the precision of the conducted test is underscored by the duplicate analysis of the standard mix and the determination of the RSD % regarding the asymmetry factor, which was consistently below 1% for all three liners, as illustrated in Figure 5.
Figure 4. Chromatograms of 4-methyl-2-pentanone when FOCUS (top), TAPERQW (middle) and STRQW (bottom) liners are used.
Figure 5. Statistical analysis regarding asymmetry factor between FOCUS, TAPERQW and STRQW.
One last aspect that will be tackled within this guide is the contamination reduction. Our tests approved the fact that TAPER FOCUS ULTRA could mitigate the contamination which possibly could be coming from the column or from the used solvent (see Figure 6). This way, matrix effects are decreased, the peak shape would not be affected, and the sensitivity would not be reduced. Moreover, the contaminants could lead to an increase of the baseline, making it difficult to distinguish between analytes and instrumental noise. For an extremely visible matrix effect, TAPER FOCUS ULTRA could be the liner of choice.
The final aspect addressed in this guide refers to contamination reduction. Our experiments substantiated that TAPER FOCUS ULTRA has the capability to alleviate potential contamination originating from the column or the solvent used, as shown in Figure 6. By employing TAPER FOCUS ULTRA, matrix effects are diminished, ensuring that peak shape remains unaffected, and sensitivity is not compromised. Additionally, contaminants have the potential to elevate the baseline, posing challenges in distinguishing between analytes and instrumental noise. For situations where a pronounced matrix effect is evident, TAPER FOCUS ULTRA emerges as the preferred liner choice.
Figure 6. Contamination chromatograms when TAPER FOCUS ULTRA (top), STRQW (middle) and TAPERQW (bottom) liners are used.
Appendix I. Method
|Standard Mix test
|1-hexene, 1-decene, 1,2,4-trimethylbenzene, P-xylene, 4-methyl-2-pentanone mix of
|SCION 8400 PRO
|50°C (hold 2 min), 20°C/min to 250°C (hold 3 min)
|Flame Ionization Detector (FID) Temperature: 275°C
Air: 300 mL/min
Hydrogen: 30 mL/min
Make up (N2): 30 mL/min