Description
Degenerate four-wave mixing coupled with an electrolytic cell and capillary electrophoresis is presented as an ultrasensitive optical absorption-based detection method for small molecule environmental toxins. In this work, the advantages of coupling degenerate four-wave mixing with an electrolytic cell to induce radical cation formation of dibenzo-p-dioxin are demonstrated. The electrolytic cell is designed to oxidize tetrachlorodibenzo-p-dioxin to its radical cation form, which results in a bathochromic shift from 305 nm to 780 nm. The electrolytic cell also concentrates the dioxin onto the surface of the cathode and greatly improves the limit of detection of the technique. The electric potential, electrolyte buffer solvent system, and other parameters of the electrolytic cell are optimized for maximum detection limits with minimum detection time. In addition, the advantages of coupling degenerate four wave-mixing with capillary electrophoresis to simultaneously separate and detect Malachite Green at low concentrations are demonstrated. Capillary zone electrophoresis is utilized in the separation of Malachite Green and Crystal Violet based on their difference in mass to charge ratios, and degenerate four-wave mixing is utilized to detect them. Two lasers, 532 and 635 nm, are responsible for generating the degenerate four wave-mixing signal from the absorbing analytes, Malachite Green and Crystal Violet. The buffer solution, capillary length, capillary electrophoresis voltage, and many other parameters of this technique are optimized for rapid, sensitive and selective detection of Malachite Green. In degenerate four-wave mixing, two coherent laser beams are mixed in an absorbing medium, a thermal grating occurs resulting in a change in the refractive index, and a laser-like signal beam is generated. This nonlinear laser wave-mixing technique offers unique advantages including extreme sensitivity, high spatial resolution, high adaptability with other analytical techniques, quick analysis times, high throughput detection, and good portability for use in the field.
