The present invention discloses a combustor system and method of measuring impurities in the combustion system. The combustion system includes an up-stream fuel injection point; a down-stream turbine combustor; a flame zone in the turbine combustor comprising a plurality of axial sub-zones; an optical port assembly configured to obtain a non-axial, direct, optical view of at least one of the plurality of axial sub-zones, and an impurity detection system in optical communication with the optical port assembly.