Modern analytical chemistry must satisfy very diverse demands. Among the most important and simultaneously most difficult tasks are the continuous monitoring of substances (chiefly in industrial and environmental control) and analyses of very complicated organic and inorganic systems, often at trace concentration levels (mainly in clinical analysis, pharmaceutical research and industry, petrochemistry, etc.). For these purposes, suitable detectors must be available. Industrial and laboratory continuous analyzers have a long history. Combination of continuous monitoring with high-performance chromatographic techniques is a much more recent technique.