Listbox Rowsource based on columns

Hi I'm trying to populate a single column listbox with the column headers of a dynamic range (a1 to last column) but i can't seem to convert that range to a list ie..

a1
b1
c1
d1
etc...

any ideas how to do that? i tried rowsource but it doesn't seem to do anything

Private Sub PlanogramListBox1()

Dim LastCol As Long
 
LastCol = Sheet1.Range("CB1" & Columns.Count).End(xlToLeft).Column

PlanogramListBox.RowSource = "'Master List'!CB1" & LastCol

 
End Sub

any help would be much appreciated

Thanks,

Chris