Ultra-trace Rb detection with degenerate four-wave mixing in a graphite furnace

Abstract

Degenerate four-wave mixing (DFWM) is employed to detect rubidium (Rb) in a graphite furnace atomizer as a versatile spectroscopic method for trace element analysis at high spectral resolution. In order to further reduce the detection limit for ultra-trace Rb detection, HNO₃, NaNO₃, KNO₃ and CsNO₃ are used as chemical modifiers and the corresponding effects on the Rb DFWM signal are investigated. The experimental results show that NO₃⁻ has an enhancement, while the effects of the metals mainly depend on their ionization potentials. Among these chemical modifiers, CsNO₃ can significantly enhance the Rb DFWM signal intensity. Using CsNO₃, the detection limit was reduced from 7.02 ng mL⁻¹ to 0.90 ng mL⁻¹. This investigation indicates that nitrates, especially those with metallic ions of lower ionization potential can effectively enhance the DFWM signal intensity and reduce the detection limit, which is of special significance in ultra-trace element detection.