Last time, I wrote a blog (here) that showed a better way to configure the EZ No-Vent in the software so that the column length didn’t need to be fudged. I kept the volumetric flow the same, and showed different ways to minimize the Negative Chromatographic Effects of the reduced Linear Velocity. Today, I’m going to show you what happens when you keep the linear velocity the same after installing the EZ No-Vent.
Figure 1: 8270 Chromatogram on a 30 m x 0.25 mm x 0.25 µm Rxi-5Sil MS (cat# 13623) by Split Injection
Figure 2 – 30 m column configured as a composite column in MassHunter
Figure 3: 8270 Chromatogram on a 30 m x 0.25 mm x 0.25 µm Rxi-5Sil MS (cat# 13623) by Split Injection with the carrier gas linear velocity matched to that of the chromatogram with no EZ No-Vent installed.
Figure 4: 30 m column configured as a composite column in MassHunter. Note the volumetric flow and Average Linear Velocity.
As you can see, the tailing the plagued the EZ No-Vent chromatograms in the previous blog (here) has been eliminated by increasing the speed of the analytes through the column. When a GC-MS is run without an EZ No-Vent (Figures 1 & 2), the vacuum extends a ways into the analytical column, causing an increase in linear velocity as analytes approach the end of the column. When the EZ No-Vent is installed, the 100 µm restrictor greatly reduces this effect, causing an overall drop in average linear velocity under the same volumetric flow, reducing efficiency. Restoring the original average linear velocity appears to be the solution to the negative chromatographic effects (Figures 3 & 4).
This post first appeared on ChromaBLOGraphy: Restek's Chromatography, please read the originial post: here
