Sensitive colorimetric determination of ammonium ion in water by laser photothermal detection

Abstract
Photothermal beam deflection was combined with the established and proven indophenol colorimetric method for the measurement of trace amounts of ammonium ion in water. A 7 mW 632 nm He–Ne laser and a 4 mW 780 nm Al–Ga–As semiconductor laser provided a limit of detection below 0.25 mmol m–3.