Application of the thermal lens effect for determination of iron(II) with 4,7-diphenyl-1,10-phenanthroline disulfonic acid

A heat-induced refractive index change is used to increase the sensitivity of the spectrophotometric determination of iron(II) in a dual-beam system. An argon ion laser (514.5 nm) is used as the heating source and the intensity variation of a helium—neon laser (632.8 nm) is measured. The sensitivity is increased 7.3 times compared with spectrophotometry; the detection limit is 3 × 10^-7 M.