Photometric detection system having multiple path length flow cell

A photometric detection system for analyzing a sample fluid, the system comprising:

• a light source;
• a detector;
• a flow cell assembly including
• a tubular liquid core waveguide having an inlet end adapted for receiving a flow of the sample fluid and a discharge end adapted for discharging the flow of sample fluid, the inlet and discharge ends defining a length;
• first coupling means for optically coupling the light source to the waveguide at a first position along the length of the waveguide;
• second coupling means for optically coupling the detector to the waveguide at a second position along the length of the waveguide, the first and second positions defining an optical path length;
• and
• means for varying the second position relative to the first position whereby the optical path length is selectively varied;
• wherein at least one of the coupling means comprises a plurality of optical fibers, each of the optical fibers having oppositely disposed first and second ends, the first end of each optical fiber being coupled to the waveguide at a coupling position longitudinally spaced from the coupling position of each other optical fiber.

A flow cell assembly for a photometric detection system for analyzing a sample fluid, the photometric detection system including a light source and a detector, the assembly comprising:

• a tubular liquid core waveguide having an inlet end adapted for receiving a flow of the sample fluid and a discharge end adapted for discharging the flow of sample fluid, the inlet and discharge ends defining a length;
• an input optical fiber having oppositely disposed light receiving and light emitting ends, the light receiving end of the input optical fiber being adapted for receiving light from the light source, the light emitting end being optically coupled to the waveguide at an emission position along the length of the waveguide;
• a plurality of collector optical fibers, each of the collector optical fibers having oppositely disposed light receiving and light emitting ends, the light receiving end of each collector optical fiber being optically coupled to the waveguide at a collection position longitudinally spaced from the collection position of each other collector optical fiber, each collection position and the emission position defining an optical path length;
• and
• an optical switch having an outlet port and a plurality of input ports, the outlet port being adapted for transmitting light to the detector, each of the light emitting ends of the collector optical fibers being optically coupled to an input port of the optical switch, whereby the optical switch selectively couples a one of the optical path lengths to the detector.