Two light source reference system for a fluorometer

Abstract

A reference system utilizes pulsed arc light excitation which excitation pulses are directed onto a flow cell containing a fluorescent dye. Fluorescent light emitted from the dye is guided to a photomultiplier tube which converts it to electrical pulses. A portion of each excitation light pulse is guided by a light pipe onto a PIN diode light detector which converts these light signals to electrical pulses. A LED reference light source is pulsed to generate a plurality of reference light pulses one of which occurs between each excitation pulse. A portion of each of these pulses is guided to each of the two light detectors and two more series of electrical pulses are generated. A microprocessor then reads the four electrical pulses resulting from each pair of light pulses and performs a computation on the resulting numbers which indicates the relative concentration of the target concentration being assayed. An optical system masks the excitation light pulses and the emitted light pulses to minimize the amount of scattered excitation light that gets into the emitted light optical channel and spatially integrates the images of the arc yielding the excitation light to control the stability of the image projected onto the photomultiplier tube. The light pipe and an output lens spatially integrates the image of the excitation light mask and focuses this light on the PIN diode so that the dancing image of the arc does not modulate with the variations of the PIN diode cathode and destabilize its output signal.