If your MATLAB does not have the Symbolic Toolbox at all, then you are out of luck (unless you get a license for Maple and install the Maple "connector" service.)
If your MATLAB does have the Symbolic Toolbox, then no matter whether you are using the newer MuPAD based symbolic toolbox or the older Maple based Symbolic Mathematics Toolbox, then you would use det()
What old enough version of MATLAB do not have is the syntax
syms NAME [rows, cols]
but in those old versions, you can
NAME = sym('NAME', [rows,cols])
