Effects and mechanisms of water matrix on surface-enhanced Raman scattering analysis of arsenite on silver nanofilm

Ag nanofilm was synthesized using a modified mirror reaction and used as surface-enhanced Raman scattering (SERS) substrate for analysis of arsenite (As(III)). The SERS substrate can detect 20 and 50 μg L^-1 As(III) spiked in aged tap water and groundwater respectively. The effect of nine common ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, NO₃^-, CO₃^2-, HPO₄^2-, SO₄^2-and Cl^-) in natural water on SERS of 0.5 mg L^-1 As(III) was investigated. Na⁺ and K⁺ (100 mg L^-1) had no obvious negative effects on the SERS intensity of 0.5 mg L^-1 As(III), but Ca²⁺ and Mg²⁺ significantly decreased that of 0.5 mg L^-1 As(III) as their concentrations increased to 1 and 10 mg L^-1 respectively. NO₃^-, SO₄^2-and CO₃^2-(HPO₄^2-) had negligible, medium and significant inhibition on the SERS of As(III) respectively. The inhibition effect of Ca²⁺ might be through the formation of surface complexes with As(III) on SERS substrate. The inhibition effect of CO₃^2-, HPO₄^2-and SO₄^2- could be explained by the competitive adsorption of anions with As(III) for adsorption sites of Ag nanofilm. It was confirmed that Cl^- can activate the SERS of As(III) alone and in the presence of Ca²⁺, CO₃^2-, HPO₄^2-and SO₄^2-. The activation effect of Cl^- on SERS of As(III) could be attributed to charge transfer (CE) mechanism.