TextFragmentAbsorber for exact words or phrase's

Hi team I have a project where i am using AsposePdf.Text. I am using the TextFragmentAbsorber class to find S/N: and another TextFragmentAbsorber class to find S/N with out the colon. The issue I am having is when the second class is implemented it will find all of the items of the first instance (S/N:) as well as  all the items of the second instance (S/N). Is there a way to do a" match whole word" or exact search?
Thanks in advance.