An elemental analysis system includes a reactor having at least one reduction reaction zone including a metal zeolite that can reduce nitrogen oxides (NOx) to molecular nitrogen (N2) by selective catalytic reduction. Correspondingly, a method of elemental analysis includes providing a reactor having at least one reduction reaction zone including a metal zeolite and reducing nitrogen oxides (NOx) to molecular nitrogen (N2) by selective catalytic reaction on the metal zeolite.