Column vs Guard Column Calibration

[brendandamm]

Quick question y'all,

I've just noticed that I have been receiving different values for my calibration standards when I use a a guard column vs not using a guard column. For instance:

No Guard Column:
Std 1: 2ppm
Std 2: 4ppm
Std 3: 8ppm

With a Guard Column:
Std 1: 1.25ppm
Std 2: 2.75ppm
Std 3: 5.somethingppm

these are exact values but you get the idea.

Is this a common occurrence? My first thought was that the fitting between the column and guard column was not aligned and creating a dead/mixing zone which could've been skewing the data, but my other calibration standards for a different compound are completely unaffected. Any thoughts/help would be great.

B

[Gerhard Kratz]

For sure a guard column is part of the separation system.
Once a method is validated with guard column, you need to use a guard column all the time.
If you are using a 30mm long guard column than for sure it has significant impact on resolution and Rt.

[James_Ball]

Adding a guard column is like adding length to a column. There will be slight differences in peak shape which can affect peak height and peak width, to differing degrees with differing analytes. Best to calibrate after installation of the guard column.