Power Query Custom Function colum as text

Hi
if I have a custom function ;

   ( atable as table )=> 
let
    Custom1 = atable,
    #"Added Custom" = Table.AddColumn(Custom1, "Custom", each let txt = List.Select( Text.Split( [Text], " "), (A)=>  Text.Length( A ) = 8 ) ,
 rs = List.Select(  txt, each
  Text.Start( _, 3 ) = Text.Upper(  Text.Start(_,3)) 
                             and Value.Type( Number.From ( Text.Middle( _, 3,3))) = type number  
                              and Text.Lower( Text.End(_,2)) = Text.End(_,2) ) 
           in Text.Combine(  rs, ", " ))
in
    #"Added Custom"

but I do not want the column hard coded Text.Split( [Text], " "),

so I added the column as a variable in the function, ( atable as table, col as text)=>

but this does not seem to work and not sure why? I did think Table.Column( atable , col ) but pretty sure this would be a list so no good ,
anyway end up with the added column but it's blank, what am I doing wrong.

Richard.