Dimensions of Guard Column Zorbax?

Dears;

We need your help about the product below:

Product Name: Mupirocin Ointment BP

Test: Related substances

Subject: Guard Column

In Related substances, it is written : When the chromatograms are recorded under the prescribed conditions the retention time of mupirocin is about 13 minutes.

Column: Zorbax C8 7µm, 250 x 4.6mm fitted with a stainless steel guard column packed with the same material.

Remark:

Without Guard Column, the retention time of Mupirocin is about 7.1 minutes.

Question:

What are the dimensions and brand of the Guard Column to be used to obtain retention time of mupirocin at about 13 minutes.