Signal-to-noise ratio enhancement of the compact light-emitting diode-induced fluorescence detector

To enhance the SNR (signal-to-noise ratio) of the compact light-emitting diode-induced fluorescence detector (LED-FD) ([14]), key parameters including LED and its coupling style, pinhole diameter, calibration, and refractive index matching fluid (RIMF) were optimized. A 20 mA LED with light intensity of 8400 mcd was used as new light source. To optimize pinhole diameter, a theoretical analysis based on a three-dimensional (3D) view of the detection area was proposed and validated experimentally. A calibration principle from the 3D perspective was proposed. The detection flow cell and the collection fiber were adjusted to be coplanar. RIMF (glycerol) was applied to enhance SNR. The performance of the improved LED-FD was evaluated by flow injection analysis (FIA). The limit of detection (LOD) was determined as 0.15 nM sodium fluorescein (SNR=3). Compared with our previous work, a five-fold enhancement on the SNR was obtained. The LOD was about five times higher than that of commercial Agilent G1321A FLD which employed a xenon pulse lamp.