On the potential of forward-scattering degenerate four-wave mixing detection in capillary electrophoresis Original Research Article

The question is addressed, whether in capillary electrophoresis (CE) the laser-based forward degenerate four-wave mixing (F-D4WM) detection method can become a realistic alternative to conventional ultraviolet (UV) absorption detection. In order to answer this question F-D4WM experiments at 351 nm have been performed. As test analytes the herbicides dinitro-ortho-cresol and dinitro-(tert-butyl)-ortho-phenol (trivial names DNOC and dinoterb, respectively) were used without derivatisation. These compounds show moderate absorption (molar absorptivity 4000 M−1 cm−1) at 351 nm under the conditions (buffer pH 8.2) used for CE separation. The detection limits obtained (1 μM) were 25-fold better than with on-column absorption detection at 351 nm. This result is shown to be typical for CE, where commonly buffer solutions with a high water content are used. For micro-separation systems that are compatible with liquid solutions with a low water content F-D4WM detection has a much wider potential.