Sensitive absorption-based wave-mixing detector for anthracycline drugs separated by capillary electrophoresis

Sensitive absorption-based detection of anthracycline antibiotics, daunorubicin and doxorubicin is demonstrated using a capillary electrophoresis system interfaced to a nonlinear wave-mixing detection system. Unlike conventional absorption methods, this nonlinear absorption method can detect very thin analytes (50 μm) efficiently. At the same peak height, the wave-mixing CE peak is narrower than a conventional CE peak, and hence, compared to other laser-based or non-laser-based CE on-column detection methods, our wave-mixing detection method offers intrinsically enhanced separation resolution even when using identical CE separation conditions. In this unusually sensitive “absorbance” detection method, two input laser beams interact to produce a thermally induced grating from which coherent laser-like wave-mixing signal beams are created. Using our sensitive “absorbance” on-column CE detector, we report a preliminary concentration detection limit of 9.9 × 10−10 M using a 50-μm i.d. capillary column. The corresponding “injected” mass detection limit is 9.1 × 10−18 mol using an injection volume of 9.2 nL. The corresponding preliminary “detected” mass detection limit inside the 12-pL detector probe volume is 1.2 × 10−20 M.