Identifying Reason for Column Name Returned by SELECT

I run this SELECT statement on a table:

select distinct(site_id) from chemistry order by site_id;

and in the returned set I see:

GW-21
GW-22
GW-22 +

GW-24

I want to find that row returning 'GW-22 +' because I believe it
should be 'GW-23'. However, my attempts to retrieve that row keep failing.
I've tried these statements:

select count(*) from chemistry where site_id = 'GW-22 +';
count
-------
0
(1 row)

yet,

select count(*) from chemistry where site_id = 'GW-22';
count
-------
803
(1 row)

Looking for the blank row also fails when I try to specify site_id as is
null, = ' ', or =''.

Please point me to the proper way of finding this rogue row so I can
correct the value in the site_id column.

TIA,

Rich