Optical fiber coupled light emitting diode based absorbance detector with a reflective flow cell

We present a versatile, optical fiber coupled light emitting diode (LED) li ght source based flow-through optical absorbance detector. The LED source i s readily changeable. Optical fibers are used to carry light from the elect ronics/display unit to a reflective flow-through cell and back. The cell ca n thus be located remotely from the electronics unit and the umbilical conn ection is not susceptible to electrical noise. The noise level of this dete ctor with LEDs of different emission maxima were observed to be in the rang e of 3-20 mu AU under actual use conditions, with a maximum short term drif t of 4 mu AU/min after the initial warm-up period. When the analyte absorba nce is well matched with the source emission characteristics, the detector response is linear with concentration over at least two orders of magnitude . The liquid flow path through the cell is linear with a large exit apertur e such that bubbles are not trapped in the optical path. The optical arrang ement is such that the incident light crosses the liquid flow orthogonally and is reflected back by a rear mirror to the receiver fiber. This arrangem ent reduces the refractive index sensitivity by an order of magnitude relat ive to conventional Z-path flow cells. (C) 1999 Elsevier Science B.V. All r ights reserved.