Thrombin removel His tag protein digestion - (Aug/21/2011 )

After thrombin cutting of his - tagged protein , Iam unable to purify the protein from by using size exclusion chromatography .always showing the contamination of thrombin residuals as per sds page .i am using PBS buffer for throbin cutting .
could you please give any suggestion to remove throbin removal ?

run the digest through a nickel column. the his tag and undigested protein should bind and the digested protein should pass through.