The new method 'Dynamic Derivative-Spectroscopy' (DDS) is presented for contamination detection and monitoring in water. As a first application, the selective measurement of aromatic solvents is investigated. The feasibility of the new technique to measure such substances selectively at competitive measurement speed is demonstrated. Selective monitoring is in contrast to the conventional 'Total Organic Carbon'-method (TOC) which determines only the total load of organic carbon in waste water. A measurement in the ultraviolet spectral range is appropriate since water has a high transparency in the effective wavelength range of a commercial Deuterium lamp. Further, DDS is also attractive for process control in chemical industry. To enhance spectral features for discrimination between the single sample components the first and second derivative of the transmission signal are used by DDS. The DDS technique makes use of a small periodic modulation of transmission wavelength of a monochromator to generate these signals in an optical manner. The corresponding modulation of the spectroscopic signal is treated by phase sensitive detection, which results in signals that correspond approximately to the first and second mathematical derivatives of the transmission. Experimental detection limits are below 0.1 mg analyte per liter water by using 10 cm absorption path and 3 minutes measurement time.
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