CHROMATOGRAPHY
Figure 2: Using IV liners improved peak height and symmetry compared with smaller and larger liners
sizes and injection volumes. As shown in Table I, the intermediate-volume IV liner demonstrated statistically better reproducibility for peak area and height on narrow-bore columns for both injection volumes and at both partial and full capacity. Results for peak symmetry were also more reproducible using an IV liner, except for the 0.5 µL injections where there was no statistical difference, and the mid-capacity comparison where symmetry was only 0.1% better using the larger volume liner.
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peak areas and 80% showed a greater average peak height when using the IV liner. Peak width, resolution, and symmetry were not statistically different from results for the larger volume liner for most compounds, which was attributed to solvent effects causing poor peak shape for some early eluting compounds using both liners. Performance did improve for early eluting compounds when less sample was injected as well as overall for later eluting compounds, which is likely the result of the IV liner’s faster sample transfer onto the column (Figure 2). For the 0.5 µL injections, the
difference was more dramatic: every peak parameter that was investigated showed statistically significant improvements when using the IV
liner versus the smaller volume liner (Figure 1). These benefits can be attributed to the IV liner providing a narrow sample transfer band and maintaining resolution from the solvent peak. Improved performance was particularly beneficial for separating closely eluting isobaric semivolatiles, such as benzo[b] fluoranthene and benzo[k]fluoranthene (resolution of 1.83 vs. 1.93 on the smaller and IV liner, respectively).
INCREASED REPRODUCIBILITY To evaluate how consistent chromatographic performance was, the relative standard deviations (%RSD) of averaged parameters across all compounds in all experiments were compared across the different liner
OVERALL ASSESSMENT Table I summarises the statistical results of all the experiments and provides a high-level evaluation of the effects of liner choice on chromatographic performance when using narrow-bore GC columns with splitless injection. Of the 50 comparisons, 43 (86%) showed the intermediate-volume IV liner provided improved (22/50) or equivalent (21/50) performance compared to smaller and larger volume liners. Results were most pronounced for area and height, which are critical for accurate peak identification and quantification. Effects were more varied for width, resolution, and symmetry, but these parameters can also be strongly affected by the other method conditions (isothermal temperatures, column phase, solubility, etc.) and elution time. Based on this data, IV liners
provide more balanced and improved chromatographic performance compared to smaller and larger volume liners. When using IV liners with narrow-bore columns, more sample can be injected compared to smaller liners, reducing the negative effects caused by solvent and liner capacity. In addition, compared to larger volume liners, the sample is introduced onto the column more quickly and in a narrower band, taking better advantage of the column’s intrinsic high efficiency. In conclusion, the intermediate volume of IV liners contributes to fast, sensitive, and highly reproducible analyses, which allows labs to maximize the benefits of narrow-bore columns. n
Table 1: Of the experimental comparisons evaluated, 86% (43/50) showed better performance or no statistical difference when using an IV liner with narrow-bore columns
Dr Mark Badger is Product Manager at Restek.
www.restek.com
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