Using A Variable In SQL Script (Declare @x)

I am not sure why the following does not work...

I am declaring a variable to hold a string to be used in my script. The contents of the variable looks perfect and works independently, the variable it does not work. (BTW, do you call this a variable in T-SQL too?). The idea is to pass the value to the script to generate different results sets.

//Parameter
DECLARE @Codes varchar(8000);
SET @Codes = '''07-1110_CHA,1'',''07-1110_DCV,2''';

//Examine contents - results: '07-1110_CHA,1','07-1110_DCV,2'
Select @Codes;

//Works fine
Select screening_cd,check_amount
From accounting
Where screening_cd in ('07-1110_CHA,1','07-1110_DCV,2');

//This does not work
Select screening_cd,check_amount
From accounting
Where screening_cd in (@Codes);

TIA