CHROMATOGRAPHY
injected, without risking backflash or compromising on peak characteristics, Restek has developed an intermediate- volume (IV) liner, that has a 3 mm ID. Compared to smaller volume liners, IV liners allow injection volumes to be doubled because they have significantly more room to contain the solvent vapor cloud. And, since IV liners have faster sample loading capabilities than larger volume liners, good chromatographic performance is maintained because the analytes spend less time in the inlet.
Boosting Narrow BORE COLUMN PERFORMANCE
Te benefits of high-efficiency, narrow-bore columns can only be fully realised when sample introduction is also optimised. Dr Mark Badger explores a novel way to improve chromatography and reproducibility
F
aster analysis times can improve lab productivity, but only if chromatographic performance still allows
accurate peak identification and quantification. Narrow-bore GC columns (<0.25 mm ID) speed up analysis because they have greater chromatographic efficiency, which produces tall, narrow, symmetrical peaks that are easy to identify. While using narrow-bore columns can be a good approach to creating fast, highly efficient chromatography with a typical GC-MS setup, their effectiveness is limited by sample introduction. A variety of sample introduction options are available but split/splitless inlets are the most common. For these inlets, liners with internal diameters of ~2 mm or ~4 mm are typically used. The smaller volume liners (~2 mm ID) transfer sample onto the column faster and in a narrow band, which can improve resolution, decrease the splitless hold time, and minimise adverse interactions, such as adsorption and reactivity. However, lower liner volume means less sample can be injected, which can reduce
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sensitivity and reproducibility. In contrast, larger volume liners (~4 mm ID) provide greater sample capacity, which can improve sensitivity and reproducibility, but their lower flow rates can cause band broadening, wider peaks, poor resolution, and analyte degradation due to the longer residence time in the liner. Ultimately, when choosing between larger and smaller volume liners, tradeoffs must be made in terms of capacity and chromatographic performance.
A MORE BALANCED SOLUTION To give narrow- bore column users more flexibility and allow additional sample to be
IMPROVED CHROMATOGRAPHY To assess the performance of IV liners versus larger and smaller liners when used with narrow-bore columns, we compared peak characteristics and resolution of 51 semivolatile compounds analyzed on an Rxi- SVOCms column (20 m x 0.15 mm ID x 0.15 µm). To avoid exceeding maximum liner capacities, six 0.5 µL injections were made on the IV and smaller liners, and six 1 µL injections were made on the IV and larger liners. When comparing the 1 µL injections, peak area and height were significantly improved (p < 0.05) for most compounds when using the IV liner, making peak identification and quantitation easier and more accurate. As shown in Figure 1, 92% of compounds showed greater average
Figure 1: Effect of liner on chromatographic performance for semi-volatiles on a narrow-bore colum
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