Absorbance detector based on a deep UV light emitting diode for narrow‐column HPLC

A detector for miniaturized HPLC based on deep UV emitting diodes and UV photodiodes was constructed. The measurement is accomplished by the transverse passage of the radiation from the light‐emitting diode ( LED ) through fused‐silica tubing with an internal diameter of 250 μm. The optical cell allows flexible alignment of the LED , tubing, and photodiode for optimization of the light throughput and has an aperture to block stray light. A beam splitter was employed to direct part of the emitted light to a reference photodiode and the L ambert– B eer law was emulated with a log‐ratio amplifier circuitry. The detector was tested with two LED s with emission bands at 280 and 255 nm and showed noise levels as low as 0.25 and 0.22 m AU , respectively. The photometric device was employed successfully in separations using a column of 1 mm inner diameter in isocratic as well as gradient elution. Good linearities over three orders of magnitude in concentration were achieved, and the precision of the measurements was better than 1% in all cases. Detection down to the low micromolar range was possible.