Dual-wavelength light-emitting diode-based ultraviolet absorption detector for nano-flow capillary liquid chromatography

The design of a miniaturized LED-based UV-absorption detector was significantly improved for on-column nanoflow LC. The detector measures approximately 27 mm × 24 mm × 10 mm and weighs only 30 g. Detection limits down to the nanomolar range and linearity across 3 orders of magnitude were obtained using sodium anthraquinone-2-sulfonate as a test analyte. Using two miniaturized detectors, a dual-detector system was assembled containing 255 nm and 275 nm LEDs with only 216 nL volume between the detectors A 100 μm slit was used for on-column detection with a 150 μm i.d. packed capillary column. Chromatographic separation of a phenol mixture was demonstrated using the dual-detector system, with each detector producing a unique chromatogram. Less than 6% variation in the ratios of absorbances measured at the two wavelengths for specific analytes was obtained across 3 orders of magnitude concentration, which demonstrates the potential of using absorption ratio measurements for target analyte detection. The dual-detector system was used for simple, but accurate, mobile phase flow rate measurement at the exit of the column. With a flow rate range from 200 to 2000 nL/min, less than 3% variation was observed.