CHROMATOGRAPHY 65
Fig. 1. van Deemter curve showing the efficiencies of helium, nitrogen and hydrogen over a range of flow rates.
Te data in Table 1 shows that all three carrier gases produced the same peak areas for each of the three compounds, so there was no effect of carrier gas on sensitivity.
As expected, however, running nitrogen at a high linear velocity has the effect of reducing efficiency, which is shown in the lower number of theoretical plates and therefore reduced resolution. Te reduced efficiency (Table 1) has the effect of broadening the peaks, which is visible in the chromatogram and is shown in Fig. 2.
For analysis of samples such as
the alkane mixture, which has plenty of resolution between peaks, there would be no reason why nitrogen and hydrogen cannot be used instead of helium.
Although use of nitrogen results in a reduction in theoretical plates, this does not impact on the overall results seen here. Tere is a strong case for using nitrogen for a number of GC analyses where high efficiency is not essential.
Hydrogen performed very similarly to helium, which demonstrates why many labs are now moving their analyses to hydrogen since they can get
comparable chromatography, whilst using a cheap, readily available alternative to helium produced safely by generators.
Te price of helium is set to continue to rise so the results here show that nitrogen and hydrogen can be used as alternative carrier gases without loss of performance. Production of these gases by generators means that labs have a constant, on-demand supply of gas and are free from the annoyance of running out of gas in the night or having to move heavy cylinders around.
For more information ✔ at
www.scientistlive.com/eurolab
Ed Connor is GC product specialist at Peak Scientific.
www.peakscientific.com
Fig. 2. Chromatogram showing Decane, Undecane and Dodecane run using helium, nitrogen and hydrogen carrier gases.
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