Miniaturized on-line trace analysis

A measuring apparatus comprising:

• an apparatus for forming a liquid optical waveguide comprising a silicon wafer as a substrate (1) having an isotropically etched, spiral-shaped microchannel (2) which is provided with a coating (13) that is low-refractive in comparison with an aqueous solution, and which is covered with a cover plate (12) for forming a closed microchannel (2), whereby the cover plate (12) is provided with a further low-refractive coating (13) at least above the microchannel (2), whereby there is formed in the substrate (1) at least one feed line (6) which permits a supplying of liquid into the closed microchannel (2) and/or a removing of liquid from the closed microchannel (2), whereby a respective feed line (6) is preferably formed at the ends of the microchannel (2), and whereby there is provided at least at one end of the closed microchannel (2), preferably at both ends of the microchannel (2), an apparatus for coupling light axially into the closed microchannel and/or for coupling light axially out of the closed microchannel (2), as well as
• a light source (4) which is adapted to penetrate the closed microchannel (2) with light,
• a light detector (5), and
• a first liquid pump (9) which supplies a sample liquid (7) to the closed microchannel (2) via the at least one feed line (6, 6a).