Well your options are to parse the string directly to an inner join or to create a udf that returns a table, that you will inner join.

DECLARE @x XML

SET @x = '<i>' + REPLACE(@classification , ',', '</i><i>') + '</i>'

SELECT *

FROM MyTable a

INNER JOIN

(SELECT x.i.value('.', 'VARCHAR(7)') AS [Classification]

FROM @x.nodes('//i') x(i)) b

ON a.Classification = b.Classification

Like I said, your other option is to drop the xml into a function and inner join your table on the function.