Passing parameter in quotes

Hi,

PW='/as sysdba'; export PW

in other module I call sqlplus ${PW} (this line I unable to change!)

How I can define PW so that sqlplus calls PW in quotes i.e sqlplus '/as sysdba'

I tried like this
PW="'/as sysdba'"; export PW - no luck

Thanks in advance

$ PW='/as sysdba'
$ export PW
$ set | grep PW
.....
PW='/as sysdba'
.....
$

Thanks