Sensitive absorbance measurement method based on laser multi-wave mixing

Abstract

A sensitive absorbance measurement based on nonlinear laser degenerate four-wave mixing is demonstrated for cadmium. The cadmium ions react with dithizone to form a cadium complex which is then extracted in carbon tetrachloride and analyzed. A relatively low-power argon ion laser line at 514.5 nm is used as the excitation light source. This nonlinear laser method offers many useful features including efficient and simple optical signal detection (signal is a collimated coherent beam), excellent detection sensitivity for absorbance, and efficient use of low laser power levels, small laser probe volumes and short analyte path legnths (e.g., <0.5 mm). A detection limit of 7 fg or 0.05 ng ml for cadmium, corresponding to an absorbance detection limit of 1.8 × 10 −6 AU is reported using a flowing analyte cell at room temperature.